Oak: Ecology, Types and Management : Ecology, Types and Management [1 ed.] 9781619424937, 9781619424920

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Copyright © 2012. Nova Science Publishers, Incorporated. All rights reserved. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

Copyright © 2012. Nova Science Publishers, Incorporated. All rights reserved. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

ENVIRONMENTAL SCIENCE, ENGINEERING AND TECHNOLOGY

OAK

Copyright © 2012. Nova Science Publishers, Incorporated. All rights reserved.

ECOLOGY, TYPES AND MANAGEMENT

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ENVIRONMENTAL SCIENCE, ENGINEERING AND TECHNOLOGY

OAK ECOLOGY, TYPES AND MANAGEMENT

CLÁUDIO ALEIXO CHUTEIRA

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AND

ABRAHAN BISPO GRÃO EDITORS

New York

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Copyright © 2012 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works.

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Library of Congress Cataloging-in-Publication Data Oak : ecology, types, and management / editors: Claudio Aleixo Chuteira and Abrahan Bispo Grco. p. cm. Includes index. ISBN:  (eBook) 1. Oak. 2. Oak--Ecology. 3. Forest ecology. 4. Forest management. I. Chuteira, Claudio Aleixo. II. Grco, Abrahan Bispo. SD397.O12O1135 2011 577.3--dc23 2011048504

Published by Nova Science Publishers, Inc.  New York Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

CONTENTS

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Preface

vii

Chapter 1

Oak Forest Management João P. F. Carvalho

Chapter 2

Influence of Oak Barrel Aging on the Quality of Red Wines Pilar Rubio-Bretón, Cándida Lorenzo, M. Rosario Salinas, Juana Martínez and Teresa Garde-Cerdán

Chapter 3

Dehesas: Open Woodland Forests of Quercus in Southwestern Spain R. Alejano, J. Vázquez-Piqué, J. Domingo-Santos, M. Fernández, E. Andivia, D. Martín, C. Pérez-Carral and M. A. González-Pérez

1 59

87

Chapter 4

Oak Wood José A. Santos, João P. F. Carvalho and Joana Santos

Chapter 5

Diversification of Cork Oak Stands Traditional Production Management: A Review Sofia Knapic

151

Use of Oak Wood in Manufacture of Barrels for Preparing and Aging Wines Andrei Prida

173

Chapter 6

Chapter 7

Natural Variability and Responses to Stresses in Andalusia Holm Oak (Quercus Ilex Subsp. Ballota [Desf.] Samp.) Populations Jose Valero Galvan, Besma Sghaier-Hammami, Rafael Mª Navarro Cerrillo and Jesus V. Jorrin-Novo

Chapter 8

Oaks and Mycorrhizal Fungi Darlene Southworth

Chapter 9

Comparative Study of Physic-Chemical Characterization and Microbial Adhesion of Oak Wood with other Wood Species Soumya El Abed, Saad koraichi Ibnsouda and Hassan Latrache

Index Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

119

193

207

219 231

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PREFACE This book presents current research in the study of the ecology, types and management of oak. Topics discussed include oak wood characterization with regard to chemical, physical and mechanical wood properties; the diversification of cork oak; the use of oak wood in the manufacture of barrels for preparing and aging wines; oaks and mycorrhizal fungi and the physico-chemical characterization and microbial adhesion of oak wood with other wood species. Chapter 1 - Oak forests are a natural resource of great value and provide important environment, ecological, social and economic functions. An appropriate management and valuation of oak forests are essential in order to ensure good revenue and simultaneously provide a sustainable development. Through a proper forest management it is possible to obtain goods and services in a sustainable way that consider not only the socio-economic needs but also the conservation of the environment, the biodiversity and the ecosystem integrity. An understanding of the main aspects involved in the management of oak forests is indispensable for its sustainability and valuation. For the production of high-quality oak timber, suitable ecological conditions and proper silviculture have to be taken into account. Different research activities have provided information about the conditions and management practices for producing high-value oak timber and other multiple-uses of oak forests. This chapter presents different features of the oak forests and provides elements for their management in its multiple functions and uses. Study results on different issues related with oak management are also presented. Chapter 2 - Winemaking is a process involving several stages, with the barrel aging period having great importance in red wine quality. Wine in contact with oak wood undergoes important changes due to the contribution of numerous components characteristic of oak, mainly aromatic and polyphenolic compounds. Moreover, wood is a porous material that allows wine micro-oxygenation, so the barrel favors a series of chemical processes of oxidative type, which affect the polyphenolic content. During barrel aging, the wine increases its aromatic complexity and improves its stability, both of which increase its organoleptic quality. The extraction process of volatile and polyphenol compounds that takes place in oak barrels is very complex and depends on many factors, among which stand out: wood composition (related to the species and origin of the oak, the cooperage and the use of the barrels), the wine composition and the contact time between wine and wood. Moreover, a very important aspect is the age of the barrel, since ethylphenols can be formed as a

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viii

Cláudio Aleixo Chuteira and Abrahan Bispo Grão

consequence of the accumulation of undesirable microorganisms on wood, especially Brettanomyces/Dekkera. These ethylphenols are compounds with very unpleasant smells that negatively affect the sensory quality of wines. Furthermore, the repeated use of barrels plugs up the wood pores with the consequent reduction in micro-oxygenation. Barrel aging is a slow process, with a high economic cost that affects the final price of wines. For this reason, alternative techniques have emerged, faster and less expensive, such as the use of oak chips. Nowadays, there is a wide range of products available (types of oak, toasting, size, etc.) and different possibilities regarding the timing of oak chips addition, contact time, dose, application of micro-oxygenation jointly with this addition, etc. Depending on the type of wine to be obtained, these factors can be optimized to achieve the most quality wines. However, it should be noted that with the accelerated aging methods, quality wines can be obtained but the results provided by the barrel can be difficult to achieve. Therefore, in this chapter we have compiled the studies carried out to now on the aspects that can best influence the quality of aged wine. For this reason, this chapter is structured as follows: first we study the oak composition and the cooperage. Secondly, we discuss the influence of different parameters, such as the type of barrel (origin and oak species), the number of barrel uses or the wood-wine contact time, on the quality of this kind of wines. Next, we study the formation of ethylphenols in wines aged in oak barrels. And finally, we discuss the different aspects related to the use of new technologies for the aging of wine. Chapter 3 - The Mediterranean basin provides a classical example of man’s interaction with his environment (Thirgood, 1981), and Spanish dehesas, an open woodland forest agroecosystem created and maintained by humans and their livestock, are a clear example of this interaction. These systems span an area of nearly 3.2 million ha in Spain (Junta de Andalucia, 2005), roughly 40% of which is in the region of Andalusia (southern Spain). They are mainly covered by trees of the genus Quercus, at a density of 20- 50 trees/ha, with an understory of crops, grassland or shrubland where cattle, sheep, pigs and goats can be raised (San Miguel, 1994). Such systems require human intervention to maintain a balance between production and conservation. Chapter 4 - Oak timber is valuated for its beauty, good mechanical properties and natural durability and may have multiple uses. An understanding of the properties of oak timber and the elements that characterize wood quality is essential for its proper use. It is important to have quality control of physical, mechanical and technological wood characteristics in order to define the better primary processing and end-use. The chapter gives a characterization of oak wood with regard to chemical, physical and mechanical wood properties. Results on the wood primary processing are provided and information addressing proper technical procedures for wood sawing and drying. Appropriate timber processing techniques are described in order to obtain lumber with a good dimensional stability, avoiding cracks and warping. Adequate wood classification is required in order to optimize industrial processes and improve product quality. Quality criteria and procedures for round and sawtimber classification are referenced, and survey results concerning oak wood grading are showed. Indications of the use of oak wood for various applications are given. Chapter 5 - The objective of this work is a review on the diversification of cork oak (Quercus suber L.) stands, aiming at the mixed production of cork (always the main product) and wood (from thinning operations). This can be done without competing with the cork production, with the wood providing an extra market value and opportunities.

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Preface

ix

The trees were obtained in the South-western Portugal (cork production region of Alentejo). The trees were felled under an authorization due to public construction since there are strict and legally enforced regulations on cork oak felling. Oaks are considered to be a valuable source of timber for construction purposes and they are highly regarded for indoor joinery and furniture due to good mechanical properties and aesthetical value. One of the potential uses of cork oak wood is for flooring products that take advantage of the high density values (0,86 gcm-3 to 0,98 gcm-3), strength and wear and friction resistance of the wood, as well as of the pleasant macroscopic structure and color. To evaluate the most adequate flooring components to produce 3D modeling and simulation techniques were used regarding the industrial transformation. The maximization of the production yields was achieved with small logs and short dimensions components (parquet and components for multilayer composites). Further, relevant properties for flooring applications (hardness, wear and dimensional stability) were assessed. Conclusions show the technological feasibility of cork oak wood to flooring applications (with high traffic uses), and therefore a strong alternative to other oak and tropical species. Chapter 6 - The preparing and ageing of wines in barrels is a key phase in creating great white and red wines. During ageing in barrels, the extractable compounds of oak wood pass into the wine and modify its aromas and taste, bringing notes of vanilla, brioche/sweet buns, coconut, spices, smoky toast aromas, coffee, caramel…. At the same time, controlled oxidation of the substances that are present in the wine, caused by the penetration of oxygen through the barrels, has a favourable effect on the sensory characteristics of the wine such as the colour, taste and smell. Oak barrels have been used for wines since the Middle Ages. However, they were abandoned at the start of the 20th century in favour of stainless steel containers, considered more hygienic. Oak started to be used again between the 1980s and 2000 up until the present day. The reason for this is that winemakers are looking for quality and the sensory benefits that wine can gain from the oak. This stage is crucial, for the barrel that had up until then been used as a simple container, has now become an « oenological tool ». The use of wood also requires skilful handling of the process in order to bring out the best of the wine and avoid standardizing it with a dominant oak character. Chapter 7 - This work aims to highlight the importance of Quercus ilex in Mediterranean forestry. Holm oak fruits (acorns) are essential for wildlife, as well as for pig fattening in dehesas. In addition, Holm oaks are acquiring a greater interest associated with Mediterranean reforestation. In this review we present studies related to the analysis of natural variability and responses to stresses in Andalusia Holm oak populations. We present data from our own research [1-7] and those found in the recent literature, emphasizing the uses of classical morphometry, together with the modern, holistic, -omics approaches and near-infrared spectroscopy. Furthermore, we discuss the difficulty of using a recalcitrant species as an experimental system and the limitations of some of the proposed techniques. By using different approaches, we obtain a deeper knowledge on natural variability and biological processes, including growth, development, organogenesis, and responses to stresses. The present review chapter is organized according to four sections, namely: (i) the relevance, main problems and challenges related to conservation and use (Introduction); (ii) the research with this species (from the field to the lab), focusing on the last one; (iii) the

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study of variability (from morphometry to –omics technologies); and (iv) the responses to abiotic stresses, concretely to drought stress. Chapter 8 - In all species of Quercus, fine roots in the upper soil layers are ectomycorrhizal. Oak root tips are coated with a mantle of fungal tissue, and the role of root hairs is replaced by fungal hyphae extending into the soil. Oak mycorrhizal fungi include species in the Ascomycota and Basidiomycota; fruiting body forms include epigeous sporocarps and resupinate crusts that produce airborne spores and hypogeous sporcarps with spores dispersed by animal mycophagists. Acorns germinate and initiate a taproot that is not mycorrhizal, subsequently lateral roots become available for mycorrhiza formation. Seedlings within oak woodlands or near the margin of mature oaks may encounter hyphae from the mycorrhizal network of mature trees. Seedlings outside the extent of the root-hyphal network of mature trees may obtain inoculum from dispersed spores—either airborne or from mycophagous animals. Seedlings without mycorrhizas may survive one or two years, but roots of saplings become mycorrhizal. Oaks grown in glasshouse or nursery conditions may not immediately require mycorrhizas; in addition to the nutrients stored in cotyledons, water and fertilizer decrease their reliance on mycorrhizal fungi or decrease formation of mycorrhizas. Chance encounters with spores may inoculate managed oak seedlings, allowing them to increase growth in nursery conditions, but creating uncertain success when outplanted. The ability of oaks to respond to global warming by moving to higher elevations or to more northerly latitudes will depend on dual dispersal of acorns and of spores of mycorrhizal fungi. Chapter 9 - On any surface in a non-sterile aqueous (or very humid) environment, biofilm can formed. The microbial adhesion to surfaces such as plastics, polypropylenes, rubbers, stainless steel and glass is now well established. However, on wooden surfaces; very few studies have been focused on the interactions of wood and microorganisms. In this chapter, the first part describes –briefly- microbial biofilm step. In the second and the third parts, respectively, the roles of the material surface and the microbial adhesion of wood and the biofilm development are discussed. Comparative data of the hydrophobicity, electron donor-acceptor, Lifshitz–van der Waals components for oak, cedar, beech, ash, pine and teak are presented. As far as we know, the theoretical prediction of microbial adhesion on wood species as mentioned has not been reported in the literature yet. Therefore, the comparison of the theoretical adhesion of these species are finally addressed.

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Chapter 1

OAK FOREST MANAGEMENT João P. F. Carvalho University Tras-os-Montes Alto Douro, Dep. Forestry, CITAB, Vila Real, Portugal

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ABSTRACT Oak forests are a natural resource of great value and provide important environment, ecological, social and economic functions. An appropriate management and valuation of oak forests are essential in order to ensure good revenue and simultaneously provide a sustainable development. Through a proper forest management it is possible to obtain goods and services in a sustainable way that consider not only the socio-economic needs but also the conservation of the environment, the biodiversity and the ecosystem integrity. An understanding of the main aspects involved in the management of oak forests is indispensable for its sustainability and valuation. For the production of high-quality oak timber, suitable ecological conditions and proper silviculture have to be taken into account. Different research activities have provided information about the conditions and management practices for producing high-value oak timber and other multiple-uses of oak forests. This chapter presents different features of the oak forests and provides elements for their management in its multiple functions and uses. Study results on different issues related with oak management are also presented.

1. INTRODUCTION The management of oak forests may follow different aspects depending on the desired objectives, like obtaining certain wood products, protection and conservation of the environment, biodiversity conservation, aesthetics and recreation. The particularities of the oak forest environment, including the involved ecological complexity and the growing rotation of oaks, provide itself a specific forest management.

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This means that the cultural practices in oaks can not be improvised, but must consider planned objectives, taking into account the characteristics of each stand and their functions. Oak woods can supply various wood products, depending on the adopted management type. The use and value of the produced material are largely dependent on the species, the productive capacity of the site and the adoption of appropriate cultural practices in order to ensure the growth of trees with the needed size and quality for the various technological products. With a proper silviculture, preventing or reducing defects in trees, it will be able to produce trees of better quality. The obtaining of large diameters for high quality uses requires a proper and permanent management. More recently, several efforts have been made for the use of small size trees, with the development of certain products such as panels, machinery and primary processing (Thibaut, 1993). Evaluations conducted on the physical, mechanical and technological of oak wood allow their use and valuation for the construction and furniture. The optimization and choice of appropriate processing technologies (cutting, drying, gluing and finishing) make possible and profitable its use even with smaller diameters. Appropriate silvicultural practices includes the entire production cycle, from installation to final harvesting, being necessary to conduct more studies and trials. The adopted management besides considering socio-economic aspects should also respect the biological balance of the ecosystem. Equally important, is fit the species to the ecological environment, ensuring a good stability and development of oaks, considering their specific characteristics, controlling and eliminating the factors that predispose to its disappearance. In certain areas, oak woods are not properly managed. Nevertheless, it is necessary an adequate oak silviculture in order to obtain quality trees and stands for technological use. The oak silviculture requires specific and quality specialized treatment techniques Several aspects are considered in the management of the oak forests for multiple uses, such as the regulation of stand density, control of the stand structure and composition, the selection of trees, set an adequate regeneration system, and prevention of risks, among others. This chapter presents different study results and elements for the management of oak forests with particular emphasis to the oaks Quercus petraea, Q. pyrenaica and Q. robur.

2. USES AND FUNCTIONALITIES OF OAK FORESTS An interesting aspect of the oak forests is their multifunctionality. Due to their bioecological characteristics, the oaks play an important role in the conservation of the physical, environmental and biological resources. The territorial extension of some oak forests, through different environments, provides a diversity of ecosystems. Because they make the habitat for many species, oak woods are essential for biodiversity conservation. On the other hand, they are relevant in conserving and improving soil, water, climate and even the natural landscape that characterizes many regions. In addition, they provide an excellent environment for recreation and leisure. Besides these important services, oak forests are an important source of wood and non-wood products, and there is a set of human activities associated with it, contributing to an improvement of local and regional economies. Thus, oak forests provide many goods and may offer multiple productive, protective and social functions. In summary, oak forests can provide the following functions and uses:

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Oak Forest Management

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Climate mitigation and air quality maintenance; Water cycle regularization; Soil and water conservation; Biodiversity conservation; Natural landscaping; Prevention of forest fires; Educational and recreational places; Preservation of historical and cultural values; Tourism development; Creation of sylvo-pastoral systems; Production of non-wood goods; Production of firewood; Production of high-quality timber. The oaks have an important role in regulating and mitigating the climate as well as in carbon sequestration from the atmosphere contributing to reduce the "greenhouse effect". The use of timber allows the storage of carbon in the long term, to the extent that such uses safeguard over a longer period of time the carbon accumulated during the lifetime of the tree. Furthermore, long rotations allow the achievement of the objectives set by the Kyoto Protocol regarding the carbon sequestration by forest and woody materials. The oaks retain and recycle particles and dust from the atmosphere, improving air quality. An oak forest serves as good purifier of the rainwater, improving water quality. Oak woods regulate the water cycle, maintain soil quality, and increase the permeability of soils and surface evaporation. Also regulate the water flow avoiding erosion effects. Shaping a natural biocenosis, the oak forests play a unique role in fauna and flora conservation. Oak stands are included in the European Habitats Directive (92/43/EEC), which has the main objective to ensure biodiversity through the conservation of natural habitats. This directive comes from a set of agreements and initiatives, such as the Berne Convention (1979) and the Convention on Biological Diversity United Nations (1992), which seeks the protection of biological diversity, with an adequate representation throughout the territory. Look for the protection of the natural systems from degradation actions that usually follow human activities. Beyond the species also aims to the conservation of their ecosystems. The loss of species and degradation of natural systems has accompanied man for millennia, and at present is accentuated by the continuing destruction of natural forests. As mentioned in the Convention, "the conservation of biological diversity is a common concern for all humanity," and it depends for its very survival and well-being. The development of societies can not be done except ensuring the sustainability of the natural environment. The Declaration of Principles adopted at the Forest Conference in Rio de Janeiro (1992) on Environment and Development and the Ministerial Conferences on the Protection of Forests in Europe (Helsinki 1993, Lisbon, 1998), emphasize, once again, the environmental conservation as part of the economic and social development. It also promotes the consideration of biodiversity in natural resource management. It declares that the forest land should be managed in a sustainable manner to meet social, economic, ecological, cultural and spiritual needs of the present and future generations. It is established the sustainable management of forests, essential feature for the biodiversity conservation. It is a concept

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already known to science, concerned with the demographic expansion, and the natural resources overexploitation, deterioration and loss of habitat, disturbance and loss of species populations. On the other hand, ensures the continuity and improvement of an inherited nature, and its transmission to future generations. The Habitats Directive and Natura 2000 arise in this context, with a view to preserving and sustaining important ecosystems for conservation. Currently there is an increasing concern for biodiversity conservation. The intense human activity over time led to the destruction of many forests around the world, and the extinction of many species. For the conservation of fauna and flora it is therefore necessary to conserve the ecosystems in which they develop. On the other hand, some regions such as Mediterranean hold a great biological diversity being considered one of the world hot-spots (Myers, 1990). Oak forests are very rich ecosystems and many species of plants, ferns, lichens, fungi, mammals, birds and insects can be found. Many of the communities and their interactions remain not well studied and known. The oak woods create a habitat with great diversity, with specific and distinctive species that only survive in that environment. The oak forest vegetation is from a botanic and ecological point of view very important, ensuring in some regions the survival of rare and threatened plants, such as Corydalis cava, Epipactis helleborine and Lilium martagon. In general, oak ecosystems present a high floristic composition compared to other forests, which favors the diversity of fauna. The plant species of the oak forests have several biogeographic origins, which coexists or predominates in different territories, showing its great diversity. Management of oaks should ensure the sustainability and enhancement of the biological diversity. In several regions, the pine forests faces the problem of fires because of its vulnerability and propagation due to their inflammability and combustibility characteristics, favored by the presence of resins and other easily volatile compounds as well the associated vegetation type. Several pine species, such as maritime pine (Pinus pinaster) are shaped to fire, promotes fire and tends to become dominant by its occurrence. Different evidences shows that the oaks have a lower combustibility resulting in lower fire propagation which is an important feature particularly in warm climates (Valette et al., 1979; Silva and Ruas, 1988; Salas and Chuvieco, 1992). In the Mediterranean, one of the biggest problems today is the forest fire as climate conditions with hot dry summers provide favorable conditions for the occurrence of fires that are responsible each year for the destruction of large forest areas. How fires affect the biological component of a given ecosystem depends on a range of biotic and abiotic parameters that cause widely varying impacts on biodiversity. The effects of fire on biodiversity depend essentially on the status of the ecosystem and the fire periodicity. Most of the Mediterranean vegetation is adapted to fire and have developed strategies that allow resisting to this kind of disturbance. However, the man has changed the fire regime, increasing its occurrence and intensity. Most fires in the Mediterranean region are due to human activity (Quézel, 1976; IFN, 2003). Only 5% of fires are caused by natural causes (lightening). Some national plans for the defense of forest fire aim to increase the resilience of the territory against forest fires, and that can be achieved with the installation and management of oak forests, slowing the fires propagation. Oak forest ecosystems also tend to create favorable microclimatic conditions that reduce the fire hazard.

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Oak Forest Management

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Oak forests are rich in edible mushrooms, such as Cantharellus cibarius, Boletus edulis, B. aereus and others. The mushrooms are important, both for culinary and commercial value. When well managed, grazing can be accomplished in oak forest understory with the use of grasses. Many oak forests developed herbaceous vegetation that may have forage utilization. The oaks provide a relevant social aspect related to recreation and leisure. They support several activities and services related to nature tourism, hunting, etc. Along with all these functions, the oaks provide high quality wood for valuable uses. Nowadays, the silviculture guidelines should consider the socio-economic context as well the perception and requirements of the importance of the multiple functions and uses of the forest. The idea of multiple-use is not new but has gained new expression in the development framework of modern society. In addition to provide wood and other goods, the oak forests, also provide protective and conservative functions of the natural resources. They are not only seen from the primary production perspective, as in recent decades, serving only particular interests, but also the interest of the collectivity. On the other hand, silviculture should seek a greater valuation of their products allowing a greater profitability and other functions. This lies in the rational use of the available resources, not just the immediate economic interest, but also ensuring its stability and increase value of their products. A proper stand management allows the obtainment of quality trees to required sizes. This may allow wood valuation and therefore contribute to a socio-economic satisfaction of rural communities. At same time it is a way for the recovery and enhancement of natural ecosystems, with positive consequences for the environment. In such a way, local and regional sector economies can be encouraged. Forestry is one of the development strategies of Europe, through products and services they can provide. Being a renewable natural resource, oaks play an important economic, social and environmental role for a sustainable development at different scales. There are possibilities for the development of new uses and valuation of the wood, creating opportunities for new products. Recent studies and developments of technological processes and knowledge about the wood properties can be used for that purpose. The concept of living and building with wood, with satisfaction of using a natural material, its contribution to sustainable development and their properties, allows its recovery. It is a natural material with excellent properties, promoting its use given its beauty, thermal and acoustic insulation, strength and natural durability. One of the difficulties associated with the multiple uses of oak forests is to assign a market value of certain services such as biodiversity and environmental protection. They may also being undervalued. Nowadays, forestry begins to discover that in addition to timber production, other services such as carbon sequestration are perfectly compatible and can generate revenues. Other important services are soil conservation and water, conservation of natural landscape, leisure and tourism, targeting benefits to local residents. Given the society demands on the concept of sustainability it is necessary to develop appropriate policy instruments for the management and valuation of oaks in its multiple benefits. Oaks play an important role in achieving European policy for the expansion and advancement of the forestry sector in particular as concerns the following aspects: development of innovative products and services and market segments; indirect goods marketing, building and living with wood; bioenergy uses; optimization of technological processes that allows greater use of woody materials; improvement of forest management

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models; development of oak forests for multiple functions and needs; increased awareness in society about the importance of oak woods valuation and their sustainable management.

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2.1. Past, Present and Future Uses Oaks represent the natural forest landscape in many areas. The formation of the current landscape resulted from the interaction of various elements, such as the biogeographical position of the territory, past climate change and more recently human activity as an important intervening factor. The existing oak forests are the result of a long historical process where natural and human interventions have occurred. Several paleobotanical works provided indications about the evolution and presence of oak forest formations from fossilized remains. Information indicates that the genus Quercus exists in America, Europe and Asia from the Oligocene epoch (34-23 mya), having diversified during the Miocene (23-5 mya) and Pliocene (5-1.8 mya) epochs. During the Quaternary (1.8 mya), the alternation of glacial and interglacial periods have strongly influenced the current distribution of oaks. The oak populations survived the coldest periods of the Quaternary glaciations in lower latitudes, such as refuge areas in southern Europe. Since the last major glacial period of Würm and, more particularly, from about 13,000 years (Tardiglacial period), oaks and other hardwood forests expanded progressively across central and southern Europe as that the climate became more cool, with an optimal period nearly 8,000 years ago (Atlantic period), with a similar biogeographic differentiation as nowadays (Salinger, 1981). The predominance of oak formations have extended and occupied the major bioclimatic regions with formation of the temperate forests to the north and northwest areas of greatest Atlantic influence, the Mediterranean forests with a maximum of drought in the southeast, and the transition woods in the sub-Atlantic to sub-Mediterranean areas. Until recently, oaks dominated many lands (Figure 1). However, with the progressively settlement of humans, through the practice of grazing and agriculture since Neolithic times (10,000 to 7,000 years ago), the natural forest was successively subjected to many pressures and changes. Although the cutting of trees is practiced since ancient times, the impact of the prehistoric people was very small. With the domestication of animals and the development of agriculture, man begins to progressively change the surrounding environment. Diverse studies (Cordeiro,1993) shown the destruction of forests and the erosion of slopes 6,000 years ago as a result of the human pressure associated with grazing and fire activities. About 3,000 years ago, many forest landscapes were already fragmented. The destruction of many forests date from the Bronze period (2nd millennium BC), as a result of the spread of burning and grazing practices (Figure 1). Since ancient times, oak has been venerated by man, and for ancient people, like the Celts, represented the supreme Mother Nature, reigning over the earth. Its domain, longevity, value and majesty explain the given feelings. However, was also a very requested tree throughout the ages for its quality and multiple uses. The oaks were an important resource of wood, acorns and leaves, for domestic uses, firewood and construction. In Europe, America and Asia, different people used the acorns in their diet. The subsequent occupation and development of settlements and agriculture led to a change in natural vegetation and landscape. Studies show different episodes of deforestation, and a relative increase in pines and shrublands as a result of human activity. The

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transhumance in mountain areas was also decisive in altering the natural landscape. The main demographic expansions that occurred cyclically throughout history, with the consequent need for more farmland, timber and firewood, were crucial periods to a marked deterioration of the primitive forests. The Middle Ages was a period of occupation and organization of the agriculture, forest and grazing territories, in which there was an irreversible break and fragmentation of many forestlands (Figure 2).

Adapted from Van de Knap and Van Leeuwen, 1994. Figure 1. Pollen diagram given a perception of the forest cover evolution from 10,000 years BP in Estrela Mountain (central Portugal). The horizontal scale represents the amount of deposited pollen for each forest/vegetation type (from left to right: Pinus, Quercus, Sum Upland Shrubs, Erica arborea, Gramineae).

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The oak wood was used for a variety of purposes, in construction and furniture making. Another important use was the manufacture of barrels, which needs a durable, strength, and proof wood. Mining, cooperage, tanning and charcoal production were also important medieval activities that consumed significant resources of oak wood. The fishing, maritime commerce, and the Age of Discovery have also required a large consumption of wood, with oak used in the construction of ships. The oak was of special relevance for shipbuilding because of its resistance, watertight and workability. There was a big consumption of large timber of various species to shipbuilding, making it a scarce material, to the point of being taken for the protection and regulation by the Navy authorities in different countries. The oak forests were being destroyed by direct or indirect action of man, through the occupation of land for agriculture, logging, fire and overgrazing. The forest policy of the royalty was primarily to defend and enforce hunting, and later throughout the fifteenth century, also emphasized the protection of the wood. Real ordinances sanctioned abuses and regulated uses. For example, in 1565 the king Filipe I promulgated the ‘Trees Act’, establishing rules for wood uses and the afforestation of uncultivated land, indicated species such as oak, chestnut and pine, being an important milestone in the history of forest resources. Some religious orders also promoted reforestation of land and cutting regulations.

Figure 2. The Middle Ages was a period of large forestland occupation and organization.

A wood crisis for construction and energy was stressed in the sixteenth and seventeenth centuries. The climate cooling that occurred during the 'Little Ice Age' (16th-18th centuries) have also enhanced the consumption of firewood. The concerns of different governments for the preservation and promotion of forest areas became manifest over different periods in our recent history, and an important progress was given with the creation of the General Administration of Forests. Subsequent actions promoted in the early days of the Forest Services. In addition to fixing the coastal dunes, in many areas they looked to the restoration of forests, and soil and water conservation.

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The advent and construction of several railways since the latest 19th century to mid 20th century, was also made with the destruction of many oaks. In certain areas, governmental campaigns to launch cereal crops in the early 20th century also contributed to the occupation of many forestlands. Over the last decades, some forest policies favored the tree-planting programs to benefit other forest species, especially fast growing species (e.g, pines, eucalyptus), in detriment of oak forests and sustainable forest management. Nowadays, in many cases there is a more or less important fragmentation of oak forests, which leads to some conservation problems, such as the recovery of wildlife. A crescent abandonment of marginal agricultural land and less consumption of firewood will allow a recovery of oak forests. Similarly, a greater awareness of the society about the conservation and restoration of natural ecosystems, combined with demanding for recreation and tourism related activities will also enhance a new direction of the forest management. Nowadays, oak wood is used for various purposes (flooring, carpentry, furniture, and cooperage). Some traditional uses, such as tanning and shipbuilding, are no longer used or have reduced its activity. Industry and companies have developed different products of oak wood (building structures, furniture), combining traditional or modern design with manufacturing techniques, using its natural strength and beauty.

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3. OAK STAND DEVELOPMENT STAGES The different cultural interventions in oak stands are, among others, determined by the stand development stage. Various terms have been used to describe the different development stand stages. These stand structural stages can be found in different publications like Frelich and Lorimer (1991) and Goodell and Langendoen (2007). In even-aged managed stands, five stages can be distinguished. The specific stand dimension for each stage depends on the species height growth pattern. Based on silvicultural and growth studies with Pyrenean oak (Q.pyrenaica), the Table 1 presents the differentiation of the different development stages for this species. Table 1. Stand development stages for Pyrenean oak stands Stand stage Regeneration Sapling Pole Young-mature Mature hd: stand dominant height; t: stand age.

hd (m) 15

t aprox. (years) > 20 > 35 > 50

The first stage is the regeneration stage, formed by young trees. Competition occurs with the spontaneous forest vegetation. In the next stage, and depending on the initial stand density, the competition among trees for water, nutrients and space increases as the canopy closes. In Pyrenean oak forests, tree height varies between 3 and 8 m, and the competition is very intense. At this stage the growth in height is fast. These two stages correspond to the

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period of application of cleaning operations. In the pole stage, height varies between 8 and 12 m, resulting in a distinct differentiation into crown classes. Selective thinning operations start at this stage. In the next stage (young-mature), the best trees are already selected. In the mature stage, the silvicultural operations will favor and regulate the diameter growth of the best trees and ensure their quality (Figure 3).

Figure 3. Different development stages of oak stands (regeneration, sapling, pole, young-mature and mature).

As trees growth from the early stages, trees are gradually differentiated into different crown classes as a result of competition. Growth in height is the most critical factor in competition. The smaller and weaker trees are progressively overtopped by other trees and eventually die. A common tree classification is based on the relative position of their crowns. Four crown classes are usually recognized: dominant, codominant, intermediate and suppressed. This classification and recognition in field is very useful in the prescription of thinning. Different thinning types define which kind of trees (crown class) to remove (Smith et al., 1996).

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In a natural forest succession, different development stages may be recognized. According to the Oliver and Larson (1996) terminology the following stages are defined: the stand initiation stage; the stem exclusion stage; the understorey reinitiation stage; and the complex stage. Each stage of succession creates the conditions for the next stage. Different disturbances (natural or silvicultural) may affect the stand structure and composition through the various stages as well their development. Silvicultural interventions may resemble, guide or altering natural processes.

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4. SILVICULTURAL SYSTEMS AND REGENERATION METHODS A sylvicultural system considers aspects related with the stand structure and composition, the method of stand regeneration as well the way of stand tending and harvesting (Baker, 1950; Daniel et al., 1982; Lanier, 1986). The features and application of different silvicultural systems can be found in specific forestry literature (e.g., Daniel et al., 1979; Burns, 1983; Smith et al., 1996). A brief description of the main systems applied to oak forests management is given. Oaks have the ability to regenerate both from seminal and vegetative sources, which enables the establishment of different silvicultural systems. These are characterized by the origin of the stand and are usually associated with different stand structure and functionalities. A high-forest is originated from seedling origin while vegetative stool sprouts lead to a coppice system. Oak coppices are characterized by having small-sized trees, both in height and diameter, and compared to the high-forest, presents a lower interest for biodiversity and landscape. They represent a lower stand development stage as a result of repeating harvestings or fires. In the past, the coppice had a greater use but since the last decades it has been abandonment and converted into high-forest. Only few oak coppices are maintained for firewood production. The various silvicultural systems follow a specific management plan and allow the achievement of different purposes. The alternation between one and another regime is possible, within certain limits, what is known as conversion. Due to the long stay of the stands, and as a result of changes in their management perspective imposed by various external factors, may be necessary to change the system, considering the implications that this may have. The conversion of coppice into high-forest is an example of common use. Evidences showed that, comparatively to the coppice and coppice with standards, the high-forest system has more interest in terms of wood productivity and quality. High-forest provides more wood per unit area and timber with better quality. The high-forest, through a proper planning and management can supply the needs of firewood as well larger timber, plus it is more productive. The woody material resulting from thinning can meet firewood needs. From the biodiversity conservation and aesthetics point of view, studies show that the highforest is of higher interest than the coppice. The stand structure can be regular or irregular depending on the frequency distribution of the trees diameters. In a regular stand structure, the distribution of diameters follows a normal distribution, and trees size is more homogeneous. Normally, trees on these stands have the same or similar ages (even-aged stands). By definition, in respect to tree age range, a stand is

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considered regular if the age width is less than 20% of the stand rotation. In opposition, an irregular stand structure follows a non-regular structure. Normally the tree diameter frequencies are descendent for larger diameters, and population is more heterogeneous, composed of trees of many different age classes (uneven-aged stands) and therefore by trees of various sizes (Figure 4). Although less frequent, a two aged or two storied stand may be also found, where a stand has two distinct ages of trees. Stands with distinct origins and structures originate different silvicultural systems, accomplish different functions, and require specific cultural treatments. The choice of a given system and structure should consider the forest characteristics, productive objectives, environmental conditions, as well ecological, social and economic constraints. Stand management for wood production follows a system according to defined objectives, and considering ecological and economic constraints. The stand density and structure are adjusted to optimize tree growth and maximize the production of the stand, given requirements for quality, vitality and stability. The high-forest is the proper system for the obtaining of a developed forest with larger trees whether or not for production purposes. The establishment of such stands type is important for protective, conservation, landscape and recreation purposes as well for quality timber production. Stand regeneration is related with the adopted silvicultural system. In a clear cutting system all trees are felled once. This system is not suitable for oaks when full natural stand regeneration is desired because seed dissemination in oaks is vertical and the need for early seedling germination protection. On the other hand, forest ground might not be full covered by new seedlings which would require a longer dissemination period. A clear cutting is mainly used in oak coppice stands where new shoots sprout easily.

Figure 4. Stand structure and trees diameter distribution (left: regular; right: irregular).

The shelterwood system is the most used in natural oak stand regeneration. The old crop is removed in two or three successive fellings spaced in time. A first seeding stage is applied through a seeding felling where good seed bearers are retained. These trees are kept well distributed throughout the stand and will disperse the seeds. Dominated and poor-shape trees are removed, while the best trees are selected as seed bearers regarding good seed production and selection of the best available genotypes. Follows one or more secondary fellings that opens the canopy to provide sufficient light to the established oak seedlings. The number and time interval of secondary cuttings varies depending on site conditions and regeneration

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establishment. The last stage consists in the final felling which removes the remaining crop trees. This felling is applied when the young stand is well established. Blanks may be restocked artificially by planting. Under favourable conditions the regeneration period may vary between 10 – 15 years according to species, seed production and site conditions. The periodicity of good mast production may also vary depending on species and climate. For common oak and sessile oak it ranges between 3 – 5 years in cool climate while in more severe conditions it is less frequent. This regeneration system might be uniform which means that is applied over a whole compartment of variable size and an even-aged and regular stand is obtained. The shelterwood system offers protection to sensitive species in early ages against frost, wind and drought. The soil is more protected comparatively to the clear cutting system with less desiccation, erosion and invasion of forest vegetation. The quality of the next stand generation might be enhanced through a positive selection of the seed crop trees. An irregular high-forest consists in a system with multiple tree ages. Young trees are originated from seeds that germinate in gaps created by the cutting of single or groups of trees. Therefore, this system is also called single-tree or group-tree selection system, respectively. Trees are harvested when they reach the target size or to regulate stand stocking and tree competition. The regeneration is established naturally in explored gaps from existing trees in the stand. Stand management involves the growth of trees of all diameter classes, with decreasing frequencies by class of diameter; the use of natural regeneration in gaps created by the cutting of the larger trees; and cultural thinnings to regulate the stand density and competition among trees. The harvesting of larger trees is done progressively to preserve the forest environment. The application of this system with light-demanding oak species must consider some requirements particularly with regard to the distribution of the trees and the size of the elementary stand. In such selection system, single-trees or group trees are periodically felled for regeneration and an uneven-aged system is obtained and maintained. Mature trees are replaced regularly by new ones through periodic and selective fellings. Regeneration, tending and harvesting are applied simultaneously in a continuous process of selection and improvement. The general purpose is to keep a balanced stand where all tree sizes are intermixed and represented equally following a size descending distribution (Figure 4). A desired growing stock is specified and a felling programme (nature, intensity and cycle) is defined to provide a sustainable yield. For light-demanding oak species the group selection system is more appropriate where trees are felled in small groups to create gaps of sufficient size to enable regeneration establishment and growth. One important advantage of this system is that provides a continuous forest cover. Soil erosion, wind and snow damages are reduced. Stand regeneration may be continuously used and seedlings protection is provided. It is an interesting system regarding protective, biodiversity conservation and aesthetics issues because a permanent structure is obtained without major disruptions and changes in forest covering. Wood production can be associated with a proper stand management. Periodic yields and quality timber can be produced. Stand management is more demanding, requiring good tree marking and harvesting skills. Another less frequent system that might be applied to oaks is the two-storied system. Normally, two different species are involved where each one occupies a different stand layer. A shade-tolerant species is established in the understorey by natural or artificial means. One example is the mixed oak-beech stands with this last species growing in the understorey.

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5. SILVICULTURAL PRACTICES 5.1. Cleaning Cleaning intends to reduce stand density and thus the competition between the trees. It also enables to regulate stem shape and natural pruning of the trees. In general, it is a mass operation, although at the end of this stand stage might have a selective character. Certain trees excessively developed, poorly shaped and very branching should be removed. This operation can be performed using manual or mechanical cutting equipments. The execution process can be total or partial, tree by tree or in strips. In the first interventions, with tree height between 2 - 5 m, and particularly in dense stands originated from natural regeneration, a cleaning operation in alternate strips (with 2 – 3 m width) can be executed. This operation can be mechanized by using a brush-cutting machine. The cleaning frequency depends on the stand density very intense interventions and should be avoided that lead to an excessive isolation of the trees. When present, it is advisable to maintain some other tree species (e.g., Prunus, Pyrus, Crataegus, Sorbus), because of the complementary functions that they may play.

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5.2. Thinning Thinning is an important cultural intervention to regulate the stand stocking, select the best trees and provide intermediate wood yields. The first thinning usually starts at the pole stage driving the main stand until the final harvesting. Thinning have an selective character and aim to provide better growing conditions for the best trees through a gradual elimination of their competitors. An important feature concerning oaks is related to the emergence and development of epicormic shoots that sprout on the stem. This concern is even greater when it seeks the production of quality wood, because of their negative effect on wood grade (see ‘Oak Wood’ chapter). Through appropriate silvicultural treatments the development of an oak stand can be guided in order to reduce the risk of epicormic branches sprouting and growth. Epicormic shoots tend to emerge as a response to changes in the normal development of the tree, affecting its physiological balance. Some evidences showed that a genetic influence might also be present and thus some trees may produce more epicormic shoots. Their growth leads to the formation of branches and knots which decreases wood quality. The susceptibility of oak to the formation of these shoots has greatly influenced stand silvicultural treatments. Thinnings should be moderate, to benefit the best trees and maintain an understorey layer able to reduce the formation of epicormic shoots. Considering a more dynamic and practicable silviculture, the management of oak stands is based on the selection and tending of crop trees. Crop trees are the best trees of the stand, from the upper storey (dominant, codominant), and are selected at the time of the first thinning. Thinnings are applied in order to benefit the crop trees by removing their competitors, promoting their growth (Figure 5). These are selective interventions to which should be given great attention. An appropriate selection of crop trees is an essential

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condition in order to meet the production targets and obtain quality trees for higher value uses (carpentry, flooring, furniture, veener). In general, the goal is the production of trees with large diameters, with stems as straight as possible, cylindrical, without branches up to 6 – 8 m height, and with few defects (see Oak Wood chapter). Crop trees must be healthy, with good vitality, have a regular growth, quality stems without many branches, with few or without epicormic shoots and free of apparent defects (Courraud, 1987; Fol, 1987; Bouchon and Trencia, 1990). For the most demanding uses such as furniture trees with large diameters and of high quality are required, which have a high monetary value. However, new developments in timber processing technology allow the use of smaller diameters for final quality uses which permits a better oak wood valuation. The selection of crop trees must consider tree vitality, stem quality and distribution through the stand. The number of crop trees may vary between 50 -120 per ha depending on the target diameter what is related with the technological use of the wood. For instance, for the common-oak (Q. robur), average site quality and a final diameter of 60 cm, 50 - 70 crop trees are selected. The rotation of a stand for wood production under the regime of high-forest depends on the species, site quality, silviculture dynamics and the target production. Usually, it might extend up to 100-150 years or more. Therefore, the stand development is guided through successive silvicultural treatments, managing a wide range of densities from early stages, with a few thousand trees, until the final stage (Figure 6).

Figure 5. Crop trees (CT) selection and thinning application (left/right: different stand development moments).

Thinning intends to progressively release the neighbor competitors of the crop trees. Besides diameter growth of the crop trees it is also important to provide enough space to develop a balanced crown. Different thinning types can be applied in oak forests depending on species, site quality, age and management goals. Low thinning is more frequent in early and late stages, while crown and mixed thinnings tend to prevail in intermediate stages. Crown thinning favored dominant and codominant trees of high quality reducing competition around their crowns, and promotes their crown expansion and diameter growth. High-quality crop trees with the potential to produce good grade butt logs will provide good financial revenues. Another aspect to consider in oak management for the production of quality timber has to do with the growth regularity of the crop trees. For high-value uses such as veneer it is important that trees growth regularly without major variations in the growth rings width. The thinning must therefore be applied on a regular basis, avoiding long periods of intense

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competition or, conversely, phases of great canopy opening. An appropriate treatment is therefore important to obtain a steady tree growth by maintaining an adequate stand density in each moment of stand life, and therefore, the regulation of competition between trees. When necessary, tending operations may also consider the cutting operations in the understorey, regulating its cover and density.

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Figure 6. Oak crop tree near its final growing stage.

Thinning intensity depends on species, site quality and stand age. It is also related with thinning frequency. It is important to establish thinning trials for different oak species and site conditions since growth response varies according to those factors. Specific experiments will provide information about the response to thinning intensity. Oaks show a positive response to thinning with a diameter increment and reduction of tree mortality. Thinnings should be moderate and heavy interventions should be avoided. Thinning should be applied in order to provide a regular tree growth and prevent the formation of epicormic shoots, so it should be done in time. In general, the periodicity may vary between 5 to 10 years depending on the thinning intensity, age and site quality. As explained above, in a selection system the harvesting and regeneration is not applied to the whole forest, but to single or group of trees. A permanent forest cover is obtained, and different type of cuttings are applied simultaneously which have different purposes (regeneration, tending, harvesting). These felling operations are done in cycles, normally ranging from 5 – 15 years. Trees of different heights occupy different stand layers. A proper management of uneven-aged stands should consider various aspects such as the definition of a residual stocking, which is maintained in order to obtain an adequate growth and yield, an adequate diameters distribution to allow a proper regeneration and tree growth, and an optimal harvesting tree size (target diameter). The harvesting of this final diameter is not necessarily strict and can be adapted to biological, ecological and economical needs and constrains.

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5.3. Pruning Pruning is needed to obtain sufficiently well-shaped trees and to produce quality wood. Trees with a straight and cylindrical stem can be achieved through the application of pruning and a proper regulation of stand density. The aim is to obtain trees with a good straightness and roundness, fewer and small size knots, without branches and other defects (rot, cracks, etc.) up to a height of 6 m or more. These characteristics have a great influence on bole value and stand revenue, along with the useful length of the stem and the tree diameter. Generally, pruning seeks to produce a straight stem and reduce the formation of knots in the butt bole section. Pruning also promotes crown conformation and stability. This aspect is especially important in young oaks where some irregularities might appear during the growing process. In the early growth stages, the oak trees may show a weak apical dominance, which leads to the appearance of forks, which must be corrected. Pruning promotes the verticality and straightness of the young trees and encourages growth in height. Forks that are detected at a young age generally tend to remain into late tree development stages. This short, twisted and bent stems, restricting the use of trees for quality timber production. In some cases, evidences shows that the initial difficulties of some trees tend to be naturally overcome and corrected over time, as the trees grow, which indicates a major concern in the early stages. In addition, high initial densities may be used in order to promote a better tree shape. From a silvicultural point of view, it is important to ensure a sufficient number of dominant trees, with good quality to be managed until the final harvesting. The first pruning should be applied 3 - 5 years after planting or seeding, with tree height near 1.5 - 2 m. In this early growth stage, pruning consists in the removal of competing branches, branches excessively developed and most importantly the correction of forks (Figure 7). It is not necessary to prune all the trees in the stand but only a certain number of best trees, about 600 trees / ha, choosing the most vigorous, straight and vertical. The number of trees to prune is reduced as the stand grows.

Figure 7. Pruning of oak trees. Left/middle: before and after fork correction. Right: Tree prune scissors and lightweight telescopic scissors are appropriate tools. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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Figure 8. Oak trees should be pruned to promote a good grow and eliminate or reduce the presence of knots.

Different factors may influence the conformation of the trees, such as genetics, environment and silvicultural practices. These practices relates to the stocking quality, initial stand density, planting care, and the subsequent cultural treatments that modify the grow space around trees. Biotic factors such as insects and animals may also have an important effect on tree growing shape.

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Table 2. Pruning guide for oak trees Total tree height (m) 5-6 9 12

Maximum pruning height (m) 2 3–4 4-6

Number of trees / ha 500 - 600 200 - 250 200 - 250

Figure 9. Execution of the pruning cut. Pruning shears and telescopic saws; incorrect cut leaving a protruding stub and properly pruning cut without damaging the trunk, thus allowing a proper healing callus and avoiding the appearance of dead knots in the wood. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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For technological timber use, there is no interest in having trees with many branches because of the knots, which are considered defects and decrease the mechanical and technological properties of the wood. To reduce the formation of knots, high stand densities are recommend promoting the natural pruning. Studies also showed that this decreases the percentage of juvenile wood, since the production of carbohydrates are reduced resulting in a negative carbon balance. Pruning can reduce the presence and size of the knots, improve the stem roundness, and reduce the presence of juvenile wood, providing a greater usable volume. Pruning should be applied in time avoiding the appearance of dead and unsound knots, as well before the branches reach large diameters, and should not be excessive. According to silvicultural requirements, it is not necessary to prune all the trees but only a certain number of the best trees of the future main stand. About 200 to 250 trees / ha trees are pruned giving priority to the most vigorous, well formed and without forks. Based on different evaluations and experiments, the first pruning on the stem butt starts when the trees reach 5 - 6 m height, eliminating the branches up to 2 m. In the next interventions, pruning length is applied about 1 - 2 m, keeping an upper limit of 1 / 3 - 1 / 2 of total tree height (Table 2). Pruning must start in early stages, be progressive, frequent and of moderate intensity. The pruning cut should be done clear without damaging the bark ridge and the branch collar. At the same time must be done without leaving a protruding stub of the branch, allowing a good healing callus (Figure 9).

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5.4. SILVICULTURE AND WOOD QUALITY Silviculture is essential to produce wood material with appropriate characteristics. Wood quality is a relative concept defined by end-use requirements and existing technology. This means that it may be suitable for one purpose but not for another. There are different attributes that can be used to define the wood quality. They can be wood intrinsic characteristics and other more related with tree anatomy. Since wood is a biological material its formation is dependent on a wide variety of factors, both internal and external to the tree (Larson, 1969). Forest managers that want to maximize forest values need to know features that determine wood quality. Although wood quality characteristics are inherent to particular species, they can be influenced by tree growing conditions. This gives foresters opportunity to choose rotation length, stocking control on some sites, thinning and pruning. Different wood uses require different material characteristic specifications. Better wood with less or no abnormalities is used in more demanding applications such as veneer while wood with more features is selected for carpentry and rustic applications. Wood quality depends on tree genetics, site conditions and silvicultural practices. Physical and mechanical properties vary widely between trees and inside each tree. Different studies showed that there is an important genetic variability inside each population for site factors and wood quality (Nepveu, 1993). Wood density has a major influence on lumber behaviour and affects other quality characteristics (strength, durability, shrinkage). Usually, higher densities lead to higher shrinkage and processing hardness. Studies showed great individual variability, and

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explaining an important fraction of the existing variability related to wood characteristics (Becker, 1979; Nepveu, 1984). Growing speed depends on site conditions, genetic characteristics and silviculture. From a silviculture and technology point of view growth improvement must be compatible with quality and wood use. For more demanding uses such as veneer trees with thin rings are more valuable (Bartot, 1988). Heartwood density at a certain age is influenced by site conditions. Evaluations with common-oak illustrates that density increases from neutral - hygrophilous to acid – mesophilous sites. For applications of higher value, oak wood with less shrinkage, without cracks, lower proportion of sapwood, pleasant colour and grain are required. It is also important to look for regular growing for technological and aesthetic purposes. Thinning should also eliminate those trees with tension wood. Irregular shaped crowns lead to high levels of tension and wood of lower quality, cause instable wood and deformation in veneer. Management has traditionally maintained stands with high stocking to produce wood with narrow growth rings. Slower growth was believed to be necessary to produce timber for better quality uses. Trees with medium to larger diameters, clear boles and wider growth rings will be sought. Where economic return is important, systems to produce valuable crop trees will be required and integrated with a multiple outputs management systems. For veneer larger diameters are usually required although different techniques may be used to valuate medium diameters (> 40 cm). Veneer products demand high quality trees which require the right silviculture. Bole length it’s also a quality criteria. Surface appearance, colour and presence of small spots are important in aesthetic quality (Mazet and Janin, 1989). Growth ring width and regularity can be controlled by silvicultural practices besides the existing individual variations and processing technique. In general, wood with light colour, fine to medium grain, no important defects, hardiness and mechanical strength not to high is preferred. Veneer colour variations can appear due to the presence of different anatomical elements, ring width, processing techniques as well as individual variability. Cooperage is another important activity for quality wines and brandy. Oak wood is appreciated for storing and aging because of its mechanical properties, permeability, porosity, polyphenolic and aromatic substances content. Wood characteristics for barrel-making vary according to species and origin. Provenance is important and there are some preferences. Sensorial compounds characteristics are important. In general, there are not a strong relationship between grain and extractives. There are variations between species and locations. Studies show that common-oak tend to have a higher content in tannins and sessileoak more aromatic; however, there are big individual variations (Guimbertreau, 1987). Pyrenean-oak has structural and chemical characteristics ideal for barrel-manufacturing. Its chemical characteristics (polyphenols, tannins and volatile compounds) are quite similar to other species which are of recognized enological quality. Wood texture is an important characteristic for barrel for wine and brandy. Straight trees, with regular growth, without spiral grain and rich in aromatic compounds are desirable. Common-oak trees with large growth, rich in tannins and higher permeability are appropriate for brandy aging. Nowadays, valuation of small diameter trees (35 – 40 cm) is also sight as well stands submitted to a more dynamic silviculture even for brandy with fewer requirements. Some defects and singularities are excluded. Grade A is assigned to the better wood quality while grade B tolerate some features.

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Furniture usually requires good boards. The outer surface demands wood absence of defects while the inner pieces tolerate their occurrence. However, the presence of small knots and other features are appreciated since it gives a more natural appearance. Lumber dimensions and small defects for carpentry do not affect so greatly the product quality. Flooring allows the use of different timber dimensions which lets oak wood be profitable. Considering its high natural durability oak wood presents advantages in outside products such as building and garden structures and furniture, without need for chemical preservatives. Because of its resistance to radiation, climatic and biological agents it’s also of great interest in building construction along the coast. Those applications tolerates a large amount of knots and so a valuation of oak wood material. Wood colour and grain are appreciated and their features provide a natural beauty. Depending on the type of management, oak forests can provide different kind of wood products. Wood quality can be influenced by silvicultural practices. Management strategies may change product quantity, quality and value (Courraud, 1987). Log quality declines with the presence of some characteristics such as poor form (sweep, ovality, taper), large branch size, spiral grain and juvenile wood (see ‘Oak Wood’ chapter). Silviculture attempts to regulate tree growth and avoid or reduce certain defects or features. However, the presence of certain wood singularities is appreciated by consumers (Marchal and Mothe, 1992) because it gives a more natural appearance. Stocking control and pruning are two important aspects concerning stand management. Silvicultural practices may have different goals depending on the ecological and site conditions and the stand development stage. Interventions may change tree growth rate, stand yield, stand stocking and structure. The goal of high-quality oak silviculture is to produce a proportion of quality lumber. A dynamic silviculture can be applied and optimize stem quality and high productivity. A positive selection of the best phenotypes, collective and individual culture with selective thinning from the pole stage might be followed. This allows a reduction in stand rotation which has economical benefits. High-quality wood is the production target with oaks with diameters of 60 cm or larger at breast height, suitable as veneer and saw timber. High-forest for timber production is the best system to pursue which can extend to 100 – 120 years or more with large target diameters. Many coppices are a thoughtless resource and high-forest is desirable wherever possible both for economical and ecological reasons. It will also allow the accomplishment of other ecosystem functions. High-forest may render compatible timber production and firewood supply. Unlike other forest species, like poplar, oak forests cannot be established as clonal commercial plantations because of its impact on natural processes and ecosystem functioning. Thinning regimes should be designed to optimize the value of the stand synthesizing diameter increment, stand stocking and volume growth, enhancement of bole quality, and species composition. In general, the heavier the thinning the greater the diameter growth response of individual trees; however, heavy thinning may reduce stand yield and degraded bole quality of residual trees. Crown height and branch persistence may increase. Many epicormic shoots may develop as a result of non-appropriate thinning operation. Some studies reports no significant differences between tree size classes and its presence may occur in some situations due to different physiological response, environment conditions, provenance and silvicultural history. Meadows and Goelz (1998) showed in oak stands that new

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epicormic branches increased significantly after different levels of thinning and that it was greater on low-vigor trees. A survey performed by Stubbs (1986) with oak showed that different log grades may be improved in the absence of epicormic branches. Log grade A may be improved 97%, grade B 68% and grade C logs may be reduced by 167%. Because log grade has a major influence on the value of hardwood sawtimber, log grade reduction caused by epicormic shoots, particularly on butt logs, greatly reduces the value of the stand.

Bole 1 Grades (% bole volume): A (67%) and B (33%) Total bole value: 300 $USD

Bole 2 Grades (% bole volume): A (44%) and C (56%) Total bole value: 215 $USD

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Figure 10. Differential grading and value for two example boles with the same volume. Silviculture has a major influence on bole quality and value.

Figure 11. Incidence of features on the bole depending on height location (left: stem butt; right: upper stem near base crown).

Response to thinning varies with species, site, age and stand condition. Oak forests benefit from thinning but must be applied at time, type and intensity. Thinning favours the best crop trees in order to obtain vigorous and large trees, well formed, without branching and important defects up to 6 – 8 m. The presence of an accessory stand is important to obtain well formed trees. Bole quality and grade are determinant for its value. The value of a log decreases quickly as grade declines. Any cultural practice that results in a bole classification reduction significantly reduces the value of the stand (Figure 10). Shake may appear in oak trees and there are references that might be frequent in some geographical areas like in England with Q. robur and Q. petraea (Savil, 1986). Large earlywood cells can cause fractures to cell walls locally, extending the flaw and leading to fracture. Like other wood characteristics, there is much variation among individuals. Vessel size characteristics are highly heritable which means that breeding programs may produce

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23

less shake-prone trees (Kleinschmit, 1986). There are some indications that soils influence the frequency of shake, and that sound oak is normally found in soils with a reasonable proportion of clay (Brown, 1945). There are no significant relationship between vessel area and ring in the adult wood, which means that growth has no effect on vessel area. However, in the juvenile wood of adult trees there is a strong and negative correlation between ring width and vessel area (Huber, 1993). In the early stages growth deviations and forks must be corrected. Pruning is necessary to promote stem form and branch-free length. Pruning promotes straightness of young trees and stimulates height growth. Forks must be suppressed from early stages when trees are 1.5 – 2 m tall. Pruning reduces the number and size of knots and the amount of juvenile wood which are depreciative to quality. More tapered stems are formed under the influence of the live crown. Incidence of branches will have implications on log use and quality depending on their location (Figure 11). Large knots drastically reduce strength and are a major cause of downgrade in timber. Pruning must be progressive, frequent and moderate in order to avoid dead knots, reduce decay hazard and not affect tree growth. The history of the present oak stands affects their current status responses to treatment and potential for producing goods and services. Silvicultural practices are needed to determine which density level produced the greatest yield and affects tree quality. Wood productivity of oak forests may change widely according to species, site and management options. Oaks are slow to medium growing trees, but the quality of the wood generates an added value that largely compensates for growth. Moreover, it is necessary to assure supply of certain raw-material. An adequate wood and industrial valuation can be obtained even with lower yield oak stands with an appropriate silviculture and timber processing technology. This allows higher revenue for existing resources even in more limiting environments. Different studies present oak wood valuation including small diameters and more Mediterranean species (Groome et al., 1988; Janin et al., 1989; Marchal and Mothe, 1992; Carvalho et al., 2004). Several efforts have been made with different species for a better use of small to medium timber such as panels (Thibaut, 1993; Ciccarese and Pettenella, 1993). Future consumption perspectives for this type of timber are increasing which valuates small woods (ECE/FAO, 1990).

6. OAK COPPICE MANAGEMENT In general, oak species have a great capacity for emission of sprouts from adventitious and dormant buds. These sprouts come from the stump after tree cutting and in certain species (e.g., Q. pyrenaica, Q. ilex) may also arise from surface roots. For example, Pyrenean oak studies showed that numerous sprouts emerge from the root zone near the stump, which leads to a group of individual sprouts that forms secondary roots of their own, resulting in individualized trees. Cutting the tree stimulates the emission of numerous sprouts, especially from dormant buds. These buds have an endogenous origin, distributed according to the tree phyllotaxic growth and kept dormant for long periods; while the adventitious are peripheral with an irregular distribution.

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The coppice system is applicable to produce small size material in a shorter period of time, usually for firewood and charcoal as well material for the manufacture of wooden tools and tutors. The rotation period is determined by the target size of the material. Usually, rotations vary between 15 and 30 years depending on the species, site quality and desired final average diameter. A silvicultural system of this type is regenerated automatically from vegetative sprouts when trees are harvested and therefore is not necessary to apply for artificial planting or seeding. The management of a regular coppice is simple, consisting in harvesting the stand at regular intervals. An irregular coppice system can also be used. The coppice consists of different age classes. Two or three felling cycles are carried out and only the shoots that have reached the exploitable size are cut. For example, a rotation of 30 years may include two age classes and felling cycles of 15 years. The sprouting ability of the stump depends on several factors such as genetics, age, diameter, site quality, stand density, cutting season and cutting technique. The sprouting capacity tends to decrease with the stump age, and it varies according to the species. The cut of the tree should be done near the ground level, slightly tilted to avoid the accumulation of water and dust which deteriorates the stump. It is recommended that the coppicing is made during the dormant period, normally between November and February. The cut made during this period allows a greater sprouting and avoids the removal of leaves which are rich in nutrients. Experiments to analyze the influence of the time of cutting in sprouting growth and competition were carried out with Q. pyrenaica. It has showed that one year after coppicing a small number of sprouts were obtained when the cut was done between April and August. Height growth is also lower when the cut occurs between March and June (Figure 12).

Figure 12. Sprout response of Pyrenean oak for different coppicing monthly periods. Number and average height of shoots associated with each stump after one year coppicing. Overall, the average number of shoots ranged from 10 to 30, the average height from 23.3 to 70.2 cm and shoots dominant height from 39.3 to 96.7 cm. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

Oak Forest Management

25

The initial number of shoots can be very high in the order of thousands of individuals per ha, competing intensely with each other. If the initial density is very high, it is recommended to carry out a cleaning operation, cutting the shoots of the lower layers, poorly conformed and dead, which will favor the diameter growth of the remaining shoots. After coppicing, and while the shoots are not high enough to reach an appropriate size and stand cover, the area should be protected from grazing. Coppice areas of Q. ilex in south of France are protected for the first 10 years after tree felling (Ducrey and Boisserie, 1992). The use for grazing requires an opening of the coppice to favor the appearance of herbaceous species and the access of the animals. However, hydrological risks, soil erosion and degradation must be considered, particularly in hilly terrains. The coppice is, therefore, a simple management system, of automatic renewal, with a faster initial growth and short rotation. The disadvantages are the production of small size material of lower monetary value, and limited applications. It leads to a smaller soil fertility improvement compared to high-forest, have a greater risk of forest fire, limited grazing use, lower interest for bio-ecological, landscape and recreation uses, and leads to population genetics stagnation. From a silvicultural point of view, studies showed that the production of firewood can be compatible with timber production in high-forest, where the woody material resulting from cleaning and first thinning operations can meet the needs for firewood. Nowadays, many coppices are abandoned. Whenever possible, and in accordance with the established management plan, it is recommended the conversion of coppice into a high-forest system.

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6.1. Coppice with Standards It is a system where high-forest and coppice are mixed in varying proportions. The upper stages are occupied by trees or standards with different ages from seminal origin forming an uneven-aged crop, and the coppice occupies the lower storey. The coppice is clear cut in regular rotations, and a certain number of standards that have reached a derisible size are also harvested. This system is not appropriate when the production of quality wood is envisaged. Management presents some difficulties and requires technical support. Some studies showed that this system presents a lower wood productivity and quality, and offers less resistance to fire and aesthetic value than the high-forest. It is applicable in the cases where the purpose is to get a different stand structure, for protection and conservation situations. Otherwise, the conversion to high-forest is recommended.

6.2. Conversions The conversion involves the change of a silvicultural system. As mentioned before, the high-forest is the system that best ensures the production of quality timber besides its interest for biodiversity, protection and landscape. Thus when in the presence of coppice or coppice with standards, a valuation is envisaged, it is advisable the conversion into high-forest (Amorini e Gambi, 1977; Lanier, 1986; Bergez et al., 1990; Sevrin, 1996). Many coppice forests have been abandoned in several countries do to their low value and changing wood demands (firewood, charcoal).

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The conversion of a coppice to a high-forest can be done using artificial or natural regeneration. In the first case, the procedure consists in a clear cutting of the coppice followed by planting or sowing. In the second case, the stand is managed until an age and structure where good tree diameters and quality seeds are produced. This depends on the site quality, initial density and treatments intensity. This intermediate coppice stage seeks to prepare the stand for seed production in order to get a new stand from seminal origin, which have greater longevity and lower rot problems than those from vegetative origin. A common way to convert the coppice into a high-forest is to extend the rotation and obtain larger trees and initiate the seed regeneration process. The intensive selection is the operation of selecting and promoting the best trees until the final harvesting. It is possible the production of quality timber through progressive thinning in the stand. The selection takes place as soon as the stand attains certain development, with a sufficient number of good trees and well distributed. It follows the procedures mentioned for the high-forest stand management. The selection and intervention should be done before there are any conditions for the appearance of epicormic shoots and low tree stability. Evidences showed that the coefficient ‘height / diameter’ should not be over 70 and 110, respectively. The stand stocking must be regulated to avoid an abrupt isolation of the best trees.

7. GROWTH AND YIELD OF OAK FORESTS

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7.1. Site Quality Evaluation The growth and productivity of forest stands depend on the genetic characteristics of the population, the site quality and the silviculture. It is important to dispose elements related to the growth and yield in order to support the management of the oak stands. Site quality expresses the full productive potential of a stand in a given location. Stand intrinsic variables as the dominant height and age may be used to assess the site quality. Several studies have been made to evaluate oak growth and site productivity for different species and ecological conditions. Growth studies of Q. pyrenaica provide a tool to evaluate site quality. Site quality curves obtained from growth models helps management decisions through potential productivity estimations (Figure 13). The site index (SI50) corresponds to the stand dominant height at a reference age of 50 years, an indicator of the site quality. Stands with greater SI50 have a greater overall wood productivity. Table 3. Site quality classes for Q. pyrenaica stands; interval limits and central value of the site index (SI50) Site Class I II III IV V

SI50 (m) Interval [19,0; 21,0[ [16,0; 19,0[ [13,0; 16,0[ [10,0; 13,0[ [7,0; 10,0[

SI50 (m) 20,5 17,5 14,5 11,5 8,5

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Oak Forest Management

SI50 30 I: 20,5

25

II:17,5 III: 14,5

15

IV: 11,5

hd(m)

20

V: 8,5

10 5 0

0 10 20 30 40 50 60 70 80 90 100 110 120

td(years)

hd

2

1,3 (hd

1

1,3)

1 e

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1 e

0,0210 td

0,915 2

0,0210 td

1

Figure 13. Site quality curves for Q. pyrenaica stands. The hd2 is the dominant height (m) estimated at a future age (td2) (years), based on the dominant height (hd1) to the present age (td1), e is the Neper’s number (2.71828). The age used is the age at diameter breast height (td) because it is easier to measure and more stable.

The site equation can be used to estimate the development of dominant height and the site index, on a consistent and invariant way whatever the time interval and the reference age (i.e., the estimates do not vary with the chosen reference age) (Carvalho and Parresol, 2005). Table 3 shows the site index and site class interval.

7.2. Growth and Yield Models Forest managers and other professionals need predictions of stand growth and yield to establish management policies as well predict revenues for product alternatives. Knowing the resources and understanding the many biological interactions involved are essential for making good management decisions. Quantitative estimates of stand growth and yield for specific management regimes are required. These estimates may be easily computed and presented to be readily gasped by users. The purpose of modelling is to capture the essential elements of forest stand dynamics in a relatively small set of mathematical equations (Amateis, 1998). Several characteristics of forest stands make the gathering of information on

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which to base management decisions unusually difficult. Among these difficulties are the long time needed to mature a forest stand, especially with slower growing species; the slowness with which the results of a particular change or treatment may appear; the numerous possible combinations of biological characteristics and management conditions for which decisions must be made; the expenses of imposing treatments on forest stands. The use of mathematical and computer simulation is particularly useful to overcome these difficulties. As mentioned by Myers (1971), simulation involves the creation and operation of a model that resembles logically the system studied, solving a problem by following the changes that occur during model use. Only as much of the system is modeled as is necessary to answer the questions that prompt the study. With adequate mathematical relationships, the manager can predict probable future performance and yield of a forest stand submitted to different management conditions (Burkhart, 1997; Zeide, 1997). Estimation of growth, yield and economical benefits can be obtained for proposed management alternatives. These involve initial density, rotation length, thinning intensity and cycle, type of thinning and other controls. Here a yield and growth model is presented for Pyrenean oak stands. Based on different evaluations and research work carried out in Q. pyrenaica forests, a first growth and yield prediction system was developed. A computer program (QPYRENAICA) was created that allows managers to simulate operations in even-aged stands of Pyrenean oak stands and generate yield tables for different sites and silvicultural prescriptions (Figure 14). It is a variable-density whole stand model (Vanclay, 1989), providing for the first time information to forest managers and biologists. Data was analysed using statistical procedures and mathematical formulations to determine the important growth relationships and built growth and yield models as well allometric functions. The Bertalanffy-Richards function for stand dominant height (hd) and site quality estimations was used with the generalized algebraic difference approach to derive a dynamic equation (Cieszewski and Bailey, 2000; Carvalho and Parresol, 2005). A stand basal area (G) growth equation based on the Clutter (1963) model and improved with a thinning index from Bailey and Ware (1983). The third main model is a stand mortality function from Devine and Clutter (1985) to predict the number of surviving trees (N) in projection simulations, and structured as an algebraic difference equation. Other models are stand yield equations for both biomass and volume, and biometric relationships such as a height-diameter equation. Site quality evaluation is based on the dominant height growth from the initial values of stand age and dominant height introduced by the user. Stand growth and yield are expressed in terms of stem and crown biomass (dry weight) (Ws, Wc) or stem volume (Vs), up to a top diameter of 2.5 cm. Concerning silviculture, the model can handle different initial number of trees (N0), initial stand basal area (G0), thinning type and intensity. Thinning intensity is regulated by the relative basal area index (RGI) and type of thinning by the 'diameter ratio', where: RGIt = Gt / Gmaxt , with Gt the basal area of the main stand and Gmaxt the maximal stand basal area, at age t. Stand yield is presented in terms of biomass or volume according to user choice. Information about stand mortality and final diameters distribution are provided if requested by the user. The model provides indications of the evolution of several stand variables (age, dominant height, number of trees, mean diameter, basal area, stand biomass and volume), thinning and increments, according to the site quality and silviculture (initial density, rotation age, thinning

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Oak Forest Management

29

type, intensity and periodicity). The program generates yield tables for different sites and silviculture prescriptions, with information for main stand, yield from thinning, cumulative production and increments (Figure 14). It is a dynamic model where user can define rotation length, thinning intensity, type and cycle through time.

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Figure 14. Some interfaces and output of the QPYRENAICA programme management tool developed for Q. pyrenaica forests.

Forest managers can compute yield tables for oak managed stands to help the establishment of controls on his operations. Additional information is provided, such as mean tree diameter, mean tree height, final diameters distribution. Furthermore, once the controls have been established, the manager can use outputs as a guide to assist him in current operations. Based on specific growing and ecological studies, Table 4 presents, as an illustrative example, the evolution of certain parameters of Q. pyrenaica stands, whose actual values depend, among others, from the applied silvicultural treatments. The values represent certain average conditions with respect to the initial density, the growing stock, thinning type and intensity, according to a normal silviculture. The present growth and yield was derived for an average site quality (SI50: III). The table shows values for the stand before thinning, main stand and secondary stand (thinning) per hectare. These are natural stands with a stand density of about 2000 trees.ha-1 after the first thinning, which is applied when the stand reaches a dominant height between 8 to 10 m. The first thinning intensity is low and the following moderate. The thinning periodicity showed in the table at regular intervals is merely indicative. The thinning type varies between the crown and mixed thinning. Stand productivity is expressed in terms of stem biomass (Ws), crown biomass (Wc) and total biomass (Ws+c) (top diameter of 2.5 cm). The following Table 5 presents productivity values (maximum mean annual increment) of stands on different site quality classes (I to V), expressed in terms of stem biomass (Im Ws max), stem and crown biomass (Im Ws+c max), and stem volume (Im Vs max), for a reference rotation of 100 years.

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Table 4. Yield table for Q. pyrenaica stands, medium site quality (SI50: III - 14,5 m) (values per ha)

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Stand Before Thinning td years 20

t Years

hd m

24

8,7

25

29

9,9

2000

30

34

11,1

1235

35

39

12,1

40

44

13,0

45

49

50 55

G m2

Main Stand

Thinnings

N

dg cm

hg m

G m2

Ws ton

Wc ton

2000

11,1

7,3

19,3

46,2

12,6

23,6

1235

13,8

8,5

18,5

50,8

15,0

765

9,2

5,1

22,1

824

16,4

9,6

17,4

53,4

16,9

411

12,1

4,7

824

20,6

657

18,6

10,6

17,9

59,9

19,4

167

14,3

657

20,7

542

20,8

11,5

18,4

65,9

22,0

115

16,0

13,8

542

20,8

458

22,8

12,3

18,7

71,5

24,5

84

54

14,5

458

20,9

408

24,4

13,0

19,0

76,5

26,5

59

15,1

408

21,1

364

26,0

13,6

19,3

81,0

28,5

60

64

15,7

364

21,2

329

27,5

14,2

19,6

85,2

65

69

16,2

329

21,3

299

29,0

14,7

19,8

70

74

16,7

299

21,4

274

30,4

15,2

20,0

75

79

17,1

274

21,5

253

31,8

15,7

80

84

17,5

253

21,5

234

33,2

85

89

17,8

234

21,6

221

34,3

90

94

18,2

221

21,7

208

95

99

18,4

208

21,8

197

100

104

18,7

197

21,8

105

109

18,9

187

110

114

19,1

178

115

119 124

19,3 19,4

120

N

N

dg cm

G m2

Ws+c ton

Ws+c ton

Wtotal ton

Im ton/ha

Ic ton./ha

34,2

93,0

3,88

14,2

48,4

114,2

3,94

4,13

15,7

64,1

134,3

3,95

3,92

2,7

10,0

74,0

153,4

3,93

3,71

2,3

9,4

83,5

171,4

3,90

3,51

17,7

2,1

9,0

92,5

188,4

3,85

3,32

50

21,7

1,9

9,2

101,7

204,6

3,79

3,23

43

23,1

1,8

9,5

111,2

220,8

3,74

3,15

30,6

36

24,5

1,7

9,1

120,3

236,1

3,69

2,99

89,0

32,6

30

25,9

1,6

8,8

129,1

250,7

3,63

2,85

92,4

34,6

25

27,2

1,5

8,5

137,6

264,6

3,58

2,72

20,1

95,5

36,6

21

28,4

1,4

8,2

145,8

277,9

3,52

2,60

16,1

20,3

98,3

38,5

19

29,7

1,3

8,0

153,8

290,6

3,46

2,49

16,5

20,4

100,8

40,1

13

34,3

1,2

8,1

162,0

302,8

3,40

2,46

35,4

16,8

20,5

103,1

41,7

13

35,4

1,2

8,4

170,4

315,2

3,35

2,42

36,5

17,1

20,6

105,2

43,3

11

36,5

1,2

8,2

178,6

327,0

3,30

2,33

187

37,5

17,4

20,7

107,0

44,8

10

37,5

1,1

8,0

186,6

338,5

3,25

2,24

21,8

178

38,6

17,7

20,8

108,7

46,4

9

38,6

1,1

7,8

194,3

349,5

3,21

2,16

21,9

170

39,6

18,0

20,8

110,2

47,9

8

39,6

1,0

7,6

201,9

360,1

3,16

2,09

170

21,9

162

40,5

18,2

20,9

111,6

49,4

8

40,5

1,0

7,4

209,3

370,3

3,11

2,02

162

21,9

155

41,5

18,4

21,0

112,9

50,9

7

41,5

0,9

7,2

216,5

380,2

3,07

Variables and units: t – stand age (years), td – stand age at dbh level (years), hd – stand dominant height (m), G – stand basal area (m2.ha-1), N – number trees per hectare, dg – mean stand diameter (cm), hg – mean stand height (m), Ws – stem dry weight (ton .ha-1), Wc – crown dry weight (ton .ha-1), Ws+c – stem and crown dry weight (ton .ha-1) , Vs – stem volume (m3.ha-1), Im – mean annual increment (ton or m3.ha-1.year-1), Ic – current annual increment (ton or m3.ha1 .year-1) (top diameter 2,5 cm).

31

Oak Forest Management

The productivity of oak stands can vary greatly depending mainly on species, site conditions and the cultural treatments. In general, oaks may present a productivity of 2 to 8 m3.ha-1.year-1. These values refer to the maximum mean annual increment in volume of the stem. The stand increment in volume or biomass is not constant throughout its life. It is lower at early ages and then later as trees get older. Oaks are slow to medium growing species. Nevertheless, the quality of wood produced, with a greater monetary value, generates an added value, compensating for their growth. The silviculture can manipulate and control the growth of oak trees, changing the number, type and distribution of trees in the stand. Various research works have been conducted in oak stands about growth and yield, silvicultural practices and its effects on productivity. Table 5. Productivity of Q. pyrenaica stands for different site quality classes, expressed in stem biomass (Im Wf max), stem and crown biomass (Im Wf+c max), and stem volume (Im Vf max), for a reference age of 100 years SI I II III IV V

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m

Im Ws max ton.ha-1

Im Ws+c max ton.ha-1

Im Vs max m3.ha-1

26,6 22,6 18,7 14,7 10,8

5,1 4,3 3,3 2,3 1,4

5,9 5,0 4,0 2,9 1,9

7,8 6,6 5,1 3,7 2,3

hd 100 years

Table 6. Average yield of Pyrenean oak coppice stands, for different site quality classes (I, III, V); stands managed to normal growing stock (t: age; hd: dominant height, N: number of trees; dg: mean diameter; G: basal area; Ws+c: stem and crown dry weight, top diameter of 2.5 cm, Vs: stand volume, top diameter of 2.5 cm) Site Quality Class I III V

t

hd

N

dg

G

Ws+c 2,5

Vs 2,5

(years)

(m)

/ ha

(cm)

(m2.ha-1)

(ton.ha-1)

(m3.ha-1)

17 21 31

9,0 7,8 6,2

5019 4853 4487

7,0 7,0 7,0

19,5 18,6 17,3

55,2 47,6 38,0

78,8 66,2 50,5

7.3. Productivity of Oak Coppice Stands Yield of oak coppice stands may vary depending on factors such as species, site quality and forestry practices. The Table 6 shows indicative average values of some stand parameters managed in short coppice rotations, at stations different site fertility (site classes I, III and V). Stand yield, expressed in terms of stem and crown dry weight (trees with a mean diameter of 7.0 cm) can vary between about 38 and 55 ton.ha-1 and in terms of volume between 50 and 79 m3.ha-1.

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8. MANAGEMENT STRATEGIES FOR MULTIPLE USES AND FUNCTIONALITIES An interesting characteristic of oak forests is that they provide simultaneously multiple functions and uses, with environmental, economic and social benefits. The oak woods can provide wood and non-wood products depending on the associated activities and forest management. Besides the production of wood for various purposes, it may be associated with the production of edible mushrooms, grazing or hunting. Among the ecosystem services and intangibles goods can be mentioned the biodiversity conservation, soil conservation, water quality, climate enhancement and nature tourist activities. This multifunctionality is particularly important in Mediterranean regions where, due to climatic limitations, the wood productivity is more limited. The possibility to provide simultaneously these goods and services depends on the stand productive capacity, their ecological value, maturity and type of management adopted, giving more priority to one or another aspect. Effectively, the oak forests have been used for centuries by rural societies by the diversity of available resources: firewood, timber, bark, mushrooms, berries, pasture and hunting. Multiple uses are seen as a contemporary and future form of management of these forests, combining uses and activities, hunting and tourism. The oak woods are also important to provide edible mushrooms, making the interest of many collectors. Studies shows that the diversity and number of species are dependent on a variety of related factors such as the climate, stand development stage, stand density, soil characteristics, management practices and existing disturbances (Amaranthus and Perry, 1994). The fungi species and quantities vary with the stand age. In general, species diversity increases in older stands to a certain state. Evidences showed that certain species are more abundant in a more advanced development stage such as Boletus edulis. The phenology and production of fruit bodies varies between different species and is also dependent on the weather of each season or year. Several cultural practices such as the fertilization, soil preparation, thinning, or disturbances such as fire, also affect the mycological production. Regeneration cuts normally lead to a decrease in production. In certain countries and regions, it is important to create regulations for the mycological gathering activity, ensuring the persistence of mushrooms. For example, it is not convenient to harvest mature mushrooms, with low commercial value but high ecological value. Among others, the regulations can define measures related with the age and size of the mushrooms, define harvest periods, species and quantities, as well as an indication of good collection procedures (e.g., suppress the pull of mushroom’s bodies). In certain circumstances, stands located in low quality sites can meet other non-productive functions. However, often, a bad stand appearance and trees conformation may be due to poor silviculture with inadequate past cultural treatments, absenteeism, wildfires, among others. The oak forests may follow a close to nature forestry, although, which considers a compromise between the ecological functions and the production of goods and services. Cultural interventions are not excluded in stands with the major purpose of conservation and protection. Simple small-scale interventions are admissible to promote biological diversity, vitality and stability of the woods, or even to allow the accessibility to recreational purposes. The management practices should provide not only the sustainability of wood production as well as the physical environment and biological diversity.

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8.1. Grazing in Oak Forests Grazing is an activity that can be integrated in oak forests, where wood production may be associated directly, thus giving more priority to forage and livestock production or wood production. There are different domestic animals that are used, as sheep, goats, cattle, pigs and horses, depending on the requirements of each type of animal and the adopted management type. If the primary goal is to obtain quality trees, it is necessary that the normal grazing activities do not harm the trees during their early development stages, and thus it is necessary to follow certain technical requirements. Oak forests may provide different types of food (leaves, acorns, understorey vegetation) for livestock depending on the species, type of animal and season (Figure 15). Jan Feb Mar Apr May Jun Jul

Aug Sep Oct Nov Dec

Leaves Acorns Grass – Shrubs Figure 15. Seasonal forage consumptions in oak forests (leaves, buds, acorns, grass and shrub).

Table 7. Some nutritional characteristics of oak leaves, Q. pyrenaica (in vitro digestibility of organic matter, crude protein and mineral analysis) Digestibility Crude Ashes Ca Mg K P Fe Cu % protein % % % % % % ppm ppm 42.8 15.2 8.5 0.65 0.18 0.91 0.16 456.7 6.0

Zn ppm 27.0

Na ppm 81.7

Mn ppm 615.7

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Table 8. Some herbaceous species present in oak forests (Q. pyrenaica) with forage value Agrostis castellana Agrostis curtisii Arrhenatherum elatius Avena barbata Avena marginata Avena sterilis Brachypodium phoenicoides Brachypodium pinnatum Brachypodium sylvaticum Bromus diandrus Bromus hordeaceus Coronilla repanda Dactylis glomerata Festuca elegans Festuca ovina Festuca paniculata Holcus lanatus Holcus mollis Hypochaeris radicata

Lolium rigidum Lotus corniculatus Medicago lupulina Ornithopus compressus Ornithopus perpusillus Ornithopus pinnatus Poa pratensis Poa trivialis Pseudarrhenaterum longifolium Trifolium arvense Trifolium campestre Trifolium dubium Trifolium pratense Trifolium subterraneum Vicia cracca Vicia lutea Vicia sativa Vicia villosa

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In some cases, the foliage of oak trees may be used to feed the animals and thus contribute to the maintenance of the livestock. The Table 7 provides some nutritional characteristics of oak leaves, obtained from a study performed with Pyrenean oak. The foliage presents average crude protein and a digestibility relatively low compared to other more desirable tree species (e.g. ash, poplar). They are rich in Fe and Mn but low in Ca and Mg, compared with other tree species. Grazing may be performed in the oak forest understorey. The oak stands ground vegetation may have foraging interest depending on the type of livestock, season, oak forest type and the geographical location. The amount of vegetable matter that livestock uses from the understorey vegetation for their diet varies according to their needs, food preferences, and according to the time of year and grazing management. Generally, it represents a complementary feeding form, depending on the property type (private, communal), the region and livestock type. Various grasses can be found in the oak stands that have forager value. Based on vegetation studies and assessments, Table 8 presents a list of plants found in Q. pyrenaica forests with forage significance. In general, as the most desirable Leguminosae and Gramineae grasses such as Trifolium arvense, Dactylis glomerata and Holcus lanatus. In certain cases, small patches of oak woods play a partitioning role of the space between grassland and cultivation terrains. Thus a mosaic of different land uses is frequent in many territories where grazing activities are taking place. Small oak wood patches are many times managed as coppices providing firewood and small size timber for occasional uses. With regard to livestock behavior and grazing management, it is possible to draw some conclusions based on evaluations made in oak woods. Animals such as goats eat oak leaves and shoots up to a maximum height of 1.5 - 2 m, while standing on their hind legs. There is a preference of the leaves of the year because are richer in nitrogenous matter, contain less fiber and tannin levels. The young leaves are also less rich in phenolic compounds and therefore more appreciated. In coppice forests of Q. gambelii (Gambel oak, central southwestern United States) it was found that root carbohydrate reserves are lowest in the period of June to August, so an over consumption of their foliage can impair the development of trees (Léouffre, 1991). Studies in Q. pubescens forests reveal that a repeated consumption over 2-3 years, of more than 40% of biomass up to 2 m height leads to a reduction of the initial biomass replacement capacity, and therefore to his disappearance and non-renewal of an available resource (Léouffre, 1991). An initial consumption of all biomass (100% in trees 2 m height) is possible provided it is done once every two years. Intense uses decrease the number of shoots and tend to occur in groups along the branches due to the elimination of the gems that occurs with the removal of twigs. Thus, it is necessary to use an annual and seasonal grazing rotation system in several areas to allow the reconstitution of leaf biomass. However, in coppices with 4 to 8 m height, a foliage consumption at lower levels (up to 2 m height), even if total, does not lead to a decrease in leaf mass and growth of the upper crown, which may to be stimulated to compensate these losses. There are also to consider that with species such as Q. pubescens, there is a tendency for natural pruning of the lower crown levels.

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Adapted from Léouffre, 1991.

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Figure 16. Evolution of consumable biomass (DM cons: dry matter consumable) of Q. pubescens according to the rate (CR%: consumable rate) and number of repeated consumptions.

Figure 17. Pyrenean oak in a montado sylvopastoral system.

Different species and leaf types occur within the coppice, in gaps and edges, where the animal makes his choice and switch their diet depending on the available resources. However, in the same area or coppice the rate of consumption of the animal can vary greatly from one tree to another, which difficult the management of the coppice forage resource. Also in more closed coppices, with fewer gaps and more difficult accesses, the animals tend to prefer to locate and consume the forage resource located on the edges and the interior is underused. The link between timber production through thinning and vegetation control from the animals can create a vertical discontinuity on the stand and reduce the fuel load, which reduces the risk of fire and its propagation, performing a protection function. It is convenient to control the animal stocking and permanence in a certain area to avoid excessive consumption and soil compaction.

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Concerning to the canopy cover for the herbaceous vegetation utilization, it can vary depending on the site characteristics, grass composition and required production. The canopy shade affects the grass growth, production, its seasonality, composition and the forage quality (Armand and Etienne, 1996). Normally, the forage production decreases with increasing canopy cover. In Q. pubescens forests the canopy cover that offers a more effective grass production ranges from 40 to 60% (Msika cit Etienne, 1996). Negative effects on the tree quality and wood production must be weighed as well environment and ecological impacts from reducing stand coverage. Prescribed fire can be used to manage the understorey vegetation composition and the forage resource. However, in long-term shrub species covering might increase as a response of fire practice. Studies performed in Q. pyrenaica stands (Rego et al., 1991) showed that grasses are increased immediately after the fire, with a recovery of the original plant community about three years after fire, but also with an increase in the shrub component. Grazing must be prohibited during the installation of new stands (planting, seeding), until the trees have a size that allows them to overcome the aggression caused by livestock, which depends on the type of animal. The practice of fire, usually associated with grazing, should be prohibited. In certain regions, oaks are exploited in the form of a sylvopastoral system, known as Dehesa in Spain and Montado in Portugal. These are typical man-made systems located in the Iberian Peninsula territories and elsewhere in the Mediterranean region and other world areas. In the Iberian Peninsula, the most common sylvopastoral systems are with cork-oak (Q. suber) and holm-oak (Q. ilex) however, other species can be found (e.g. Castanea sativa, Q. pyrenaica, Q. faginea). In these spaces wood production and livestock husbandry activities are pursued together. A variety of animals can be grazed, including sheep, goats, pigs, cattle, horses and bulls. Oak stands have lower densities, with shorter trees, large crowns and open stand canopies, promoting a higher luminosity near the ground and a bigger development of spontaneous or seeded forage plants. Here, the tree has a primarily environmental role, protecting the soil from the effects of direct sunlight radiation and wind, thus reducing the rate of water evaporation. In addition, it improves the physical, chemical and biological soil properties, resulting in a greater benefit to support pasture and grazing, especially during the Mediterranean summer, when rainfall is scarce. On the other hand, provides shade and shelter for animals. The presence of the tree provides a softening of the environment, which is important in hot and dry environments. Furthermore, it provides branches, leaves and acorns that animals can feed when pasture is scarce, and firewood and charcoal when the branches are pruned. When properly managed, this man-made systems show a notable sustainability and biodiversity since are well adapted to local Mediterranean constraints.

8.2. Protection and Conservation This topic is related with the management of oak habitats for biodiversity conservation, as well the protection of the environment which includes aspects like soil and water conservation, climate enhancement and carbon sequestration. These oak woods functionalities are not always easy to evaluate since many benefits are considered intangible. In other cases,

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it may be targeting the promotion of game animals for hunting, where the oak forest is the proper habitat, as is the case of the roe deer (Capreolus capreolus). The conservation of wildlife can be the primary management goal of an oak forest, although it can be reconciled with other uses depending on their characteristics. The wildlife has adapted to the natural environment before man modified it. Conservation is needed due to the loss of many natural processes and forest fragmentation (McNaught and Wolf, 1984). The oak forest constitutes a habitat with a great diverse. It includes a rich flora and fauna with many with specific plants and animals that only exist in its environment. The recognition and management of distinct oak forests types is thus very important. The priorities for conservation and protection should be considered with other aspects of sustainable development (Marren, 1992). Specific uses and priorities can be framed as part of a given forest landscape, identifying the most appropriate occupation type. At the territorial level, oaks may have different functionalities depending on its characteristics and needs. The biodiversity conservation of oaks concerns with the biological and ecological diversity, considering the composition, structure and functioning of the ecosystem. The diversity varies depending on the considered spatial scale. Ecological studies show that conservation measures should consider this aspect. There is the scale of the tree, the scale of the stand, the massive scale and the scale of the eco-complex or closely related ecosystems. Forest management can, in this sense, be integrated or adapted, depending on the desired objectives (Peterken, 1977; Bormann and Likens, 1981; Marren, 1992). Management of oaks should ensure the sustainability of diversity and, when is needed, its increase. In the general case, an appropriate current management considering economic, ecological and social aspects solves most problems in terms of conservation. Simple actions such as maintenance of senescent and dead trees, and the creation of discontinuities, are examples of actions that allow the promotion of diversity. The oak forests hold diverse plants and provides habitat for numerous species of wildlife. Actions may seek to promote diversity or preserve habitats for their specific characteristics and the presence of rare or endangered species of flora and fauna. A wide variety of insects, birds and mammals is associated with the oak. The light that penetrates into the understorey allows the existence of several plant species. The canopy is diverse creating different life possibilities. In turn, the type of litter originates good humus type and enhances life at the ground level. Evidences also showed that the oaks development state is also very important for diversity of ecological niches. Thus, when the oak forest is destroyed to a great extent, its effects will be reflected negatively on diversity, in the living conditions for many species and in the physical environment conditions (e.g., drought, erosion). The oak forest management for wildlife involves the creation and maintenance of environmental conditions that meet the habitat needs of different species. Factors affecting the abundance and distribution of animals, such as tree age and size, stand composition and structure and oak distribution in the landscape. According to some evaluations, the maintenance of appropriate conditions for wildlife can be difficult and complex, especially where human activity is more permanent. The transition zones between the open space and oak wood provide a good structural diversity, which is attractive to a wide variety of wildlife, and plants that blooms in more light conditions than inside the stand. These edge areas should be managed by keeping its

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functionality, along with other vegetation mosaics. Regeneration areas provide open spaces that are colonized by several plants and animal species. Different oak tending and regeneration activities can be taken by different animals that use the new spaces for food, such as the roe deer. Studies performed with oak species (Warren and Fuller, 1993) show that the edge effect is also beneficial for many species, favoring insects, birds and mammals. However, clearings should not be excessive; birds associated with inner wood part may be subject to edge parasitism, predation and competition. In many cases, occurs a more or less important fragmentation of oak forests, which carries some conservation problems, such as the recovery of wildlife. Evidences show that the land use over time has led to smaller fragments not connected and permeable to external aggressions. The consequence is a reduction of populations associated with oak, both plants and animals, loss of biodiversity and genetic variability. Small and isolated fragments are also more prone to peripheral predation. Exchanges between populations are difficult or even impossible, particularly for species with low dispersal ability. The progressive fragmentation of the ecosystem results in a reduction of the overall quality of the habitat, which can lead to extinction of certain species. Studies performed on oaks show that the reduction of the fragments leads to an increased predation of bird nests during the spring (Stephens et al., 2003). In the edge of the forest predators can occur on both ways creating a higher pressure. In these smaller fragments it is also observed a higher consumption of fruits and seeds which reduces the capacity for tree regeneration, as well the presence of certain species such as wintering frugivorous birds. The fragments are also more permeable to other forms of degradation. The dispersive ability of certain animals is also affected, especially for those species with less ability to move and spread. Vertebrate species that are often absent or with reduced presence in small and isolated fragments are those with large territory needs (e.g. woodpeckers) or those who can not disperse through adverse territories. Some birds that live inside the forest are also affected due to competition, predation and parasitism of species associated with edges (Conner et al. 1979; Faanes, 1984; Gullion 1989). The survival of some species requires a typical forest environment may be affected by excessive fragmentation of the forest. Certain forestry practices are likely to favor certain tree species over others, for example promoting the regeneration of pine, reducing the availability of acorns and species that feed it. Other practices may, for example, stimulate the understorey vegetation, increasing the quantity and quality of food. However, certain treatments may reduce the stand diversity and complexity reducing the habitat quality. In general, and from the ecological principles point of view, small wood patches and boundary lines, resulting from the fragmentation processes, have less value and interest to wildlife, as it contains fewer species, smaller populations and less structural space. However, in areas of more intense land use, these small fragments may have a great importance as they provide a refuge for many species, providing survival and protection. Despite its lower value compared to the forest, in more humanized and exploited areas, it is important their maintenance, even for landscape and climate mitigation purposes. Sometimes constitute a reservoir of several local species. In the course of the ecological succession, there are several changes in oak stand composition and structure. These changes affect the type of food and available cover for the different species. On the other hand, several disturbances, at different scales, can occur throughout the succession like fires and windthrows creating new and different life opportunities. For example, after the occurrence of

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a severe fire with death of all vegetation, there is a spread of plants that grow in exposed places. These pioneers include annual herbaceous plants, ferns, and sprouts of some shrubs and trees. Studies show that the presence of annual species then tends to decrease in favor of perennials (Tarrega et al., 1991). Acorns are an important food source for many animals (McShea, 2000). The production of acorns is higher in well developed oaks. The presence of large trees and dead oaks, sometimes with cavities in the trunk, it’s also important for many species, providing life opportunities and niches. Trees at different stages of degradation are used by wildlife. Thinning made in oak woods should consider their effects on tree growth. The retention of dead trees and large live trees is also interesting because they are capable of supporting a wide variety of animals, insects, birds, rodents, lichens, mosses and mushrooms. Old and senescent trees provide and create multiple opportunities for many organisms, such as fungi, lichens, insects, birds and mammals. The retention of such trees is of special interest for conservation. Trees with large crowns, thick branches and holes in the trunk are particularly interesting because of the niches they create. Many birds nest in old trees and feed on insects associated with them. Studies show that dead trees also support many invertebrates and fungi (McPhail, 1993).

Figure 18. Blue Ridge Mountains. Until the early 1930s many Appalachians forests were intensively exploited, NPS (left). Until the 19th century much of the Blue Ridge was heavily forested. It was during the 19th and first years of the 20th century that much of the forestland was largely denuded by agriculture and logging activities. Entire mountainsides were cut without regard to the environment impact (deforestation, rampant fires, soil erosion, and destructive flooding). After diverse governmental and non-governmental protective programs, with the creation of national parks, the forest and landscape were recovered (right).

Table 9. Stand characteristics of an oak virgin forest (Prašnik Forest, Croatia) Parameter Average value / ha Dominant height 37 m Density of large oak trees (70 – 200 cm) 24 Tree diameter range (all species) 3 – 204 cm Average diameter of oak trees 110 cm Stand volume 571 m3 Tree dominant species: Quercus robur (60-90% stand volume). Other tree species: Acer campestre, Acer pseudoplatanus, Acer tataricum, Fagus sylvatica, Fraxinus angustifolia, Malus silvestris, Prunus avium, Pyrus pyraster, Tilia tomentosa, T. cordata, Ulmus carpinifolia, U. laevis.

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The conservation of old-growth oak woods it’s very important because of its ecological significance and rarity. Many ancient oaks were being felledover time. The loss of such forests and ecosystem is disturbing, given its unique and unusual characteristics not found in common managed forests (large and old trees, large dead trees, snags and down dead wood, cavities trees, size of secondary tree species, species diversity and ecosystem complexity). The composition of the flora and fauna, stand structure, tree size and age are interesting features of this type of forests (Table 9) (Matić et al., 1979). The recovery and reconstruction of this type of oak woods is difficult or even impossible given the long period of time required and destruction of certain elements of the some ecosystem. Restrictions to livestock and grazing may be required because of their impact on the natural vegetation composition. Grazing can affect the composition and regeneration of oaks in many ways, and especially when associated with fire. The major concern occurs in the early stages of regeneration of forest stands, the consumption of seeds and plants, and tree damage by animals. The control of wildlife animals may be needed. In particular cases, high densities of roe-deer may damage oak regeneration and young trees by destroying the bark and eat leaves and shoots. Harvesting is an operation that might have a great impact on the forest. It must consider decisions regarding the location, size and proximity of the cutting operations, requiring information about their impact on the ecological processes and wildlife. From a conservation point of view, it is preferable stand renovation from oak natural regeneration. Natural regeneration of oaks tends to have a higher genetic diversity and therefore has a greater conservation value. The aim is to encourage the successful establishment of oak in their ecological environment and keep the territorial genetic characteristics. Other aspects to consider in oak forests management for protection and conservation are as follows: -

-

-

Identify and classify priority oak forests with conservation value. Operate in the long term and controlled manner. Some species of flora are influenced by strong disturbances caused by thinning. Promote the establishment of habitats and ecological diversity by adopting simple and small-scale interventions (health check, revitalize small patches, leaving few trees in senescence). Keep certain ecotypes (associations, communities), botanically recognized. Retain stands of recognized historical interest because of their age, natural and scenic value. The older trees support a greater abundance of fauna and flora. Manage specific habitats for conservation of rare plants and animals, with or without full protection (integral reserves). Many animals, insects, birds, plants and other forms of life are associated with only certain natural forests. Assess the importance of the geographical location of certain forests. In sparsely wooded areas, the loss of any stand has much more impact than in high forested regions.

Silviculture practices include the following interventions: -

Promotion of native species, and follow a close to nature forestry. Give priority to natural regeneration and use of local seed (keep local ‘gene bank’).

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Avoid clearcuts, at least in large areas, regenerating the oak in the most natural possible way. Creation of gaps or take advantage of natural openings, helping to maintain ecotypes (transitional habitats). Creation of a more diverse stand structure, allowing maintaining more niches and increasing the stand stability. Maintain, in certain situations, longer rotations or promote stands discontinuous natural regeneration. Consider the possibility of a positive non-intervention in some stands. Exclude domestic animals; grazing eliminates many plant species, reducing the natural value of the plant communities. Control the invasion of undesirable species.

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8.3. Small Size Stands and Hedgerows In certain areas, it is the common the presence of oaks in the form of small patches or clumps, and in the edges of fields with variable density and structure. Its origin may be diverse, often resulting from human activity on the local planning of the territory, or due to micro-local situations (e.g. a rocky area) where agriculture is unfeasible. These small patches can be seen in different ways depending on their use, site quality, structure and quality of the trees. Generally, they have a secondary production role, constituting a woody reserve for occasional needs (e.g., firewood, poles). In most cases they are not managed by their low value, absenteeism, or simply lack of information and goals definition. These oak woods play an important role in partitioning the landscape and for environmental purposes such as windbreaks, especially in high and exposed areas. They also contribute for the protection of local wildlife, in addition to its recreational value. Windbreaks and belts of oaks may form important barriers against the wind, playing an important environmental action. They allow the reduction of wind speed and evaporation, prevents wind erosion, and provides protection of crops, animals and buildings. They also promote the landscape through its shape and colorations. Sometimes, in certain geographical areas, we are in the presence of low quality oak stands. These are stands with bad shaped trees or have a very low productivity. In many situations, low quality stands can meet other non-productive functions. However, the poor appearance of a stand may be due to poor management, inadequate past treatments, wildfires, pests and diseases, among others. The reasons to consider a stand of poor quality or low wood productive value can be: Low site quality: due to soil and climate limitations or poor ecological adaptation of the species into consideration; stand growth and yield is very low. Under-stocking: stand with low density, occurring usually when the spacing between trees is higher than the stand mean height. Poor quality trees: stand without or few trees with mercantile value due to poor stem straightness and the presence of defects. Inaccessibility: when access to the stand is impractical or too costly.

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42

João P. F. Carvalho Some aspects to consider oaks management are as follows: -

Ensure its perpetuation: natural regeneration is often poor, being consumed by wildlife, and it is therefore necessary to consider the planting and protection of plants in the early stages. Sometimes there is the presence of senescent trees. - Ensure stand vitality. - Density: consider the possibility of using natural regeneration and protection of plants in the early stages. - Stand rehabilitation: application of cleaning, thinning and pruning encouraging any well formed trees. - Wood production: production of lesser wood value. - Option for the coppice system for biomass production. - Grazing. It is important to characterize the stand and the potential of the site, before taking any decision. The valuation may be achieved through multiple uses in conservation, landscape and recreation.

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8.4. Landscape and Recreation Despite many current landscapes are the result of a more or less intense human activity, it is possible to provide to the existing oak forests a great landscape value, integrating them into a proper territory management. The land planning considers the different landscape components, looking to value the different units, including agriculture, forestry and ecological requirements of each region (Thomas, 1983). It attempts to maintain the balance between the requisites for sustainable conservation of the natural environment, the various functions of forest areas, and the agricultural areas and needs of the human populations. Oak forests are an important element of the landscape. They represent the natural and typical forest formation of many territories. Nowadays, many landscapes are much artificialized due to human activities such as construction, agriculture, grazing and afforestation with tree species that are not natural to the territory. The historical influence on the landscape emphasizes, then, our ongoing responsibility of how it should be managed for the posterity. This explains the importance of oak in maintaining a natural environment combined with other values and functions. Man has been using intensively the forest for millennia, and old texts report problems of forest loss and degradation. This has led to the loss of species and oak forest functionalities. On the other hand, in some areas, there has been a controversial spread of monoculture of conifers. In many geographical areas, people live surrounded by a destroyed landscape, not only due to urban disordered plans but also as a result of devastation of the natural forest. The forest restoration requires time, however, short-term political interests often impose to longterm priorities. A territorial approach of the forest areas uses and their characteristics can ensure an appropriate balance of resources use and conservation, respecting the ecological integrity of a given region.

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In addition to the income derived from wood, there is a growing recognition and appreciation of other benefits that oak forests can offer, such as landscape and recreational activities. Its use for landscape and recreational purposes does not necessarily come into conflict with wood production if good management is adopted. Ensuring compatibility between forestry and its recreational use is an integral part of forest management. The oaks are unique in their ability for recreation, in the enjoyment and appreciation of them. Several activities related to nature can be carried out taking advantage of the oak wood features. The wildlife creates an important recreational interest. Leisure and hunting can bring important economic benefits to the oak forested areas. Demand for recreation in natural areas has increased substantially in recent times. The forested areas provide rest and satisfaction, enjoy of the wildlife, flora and fauna, carrying out recreational activities and outdoor sports. Sports and leisure activities can rend important dividends, and play an important role in the oak economy. It is difficult to interpret the concept of landscape attraction, since it is subjective and is related to the individual experience, culture and education (Thomas, 1983). Nevertheless, there is a set of principles associated with the landscape design (shape, strength, scale, diversity and unity) that is considered in the planning of forest occupation of a given territory. In this sense, the oaks play an important role because they can add an important set of features such as the diversity of flora and fauna, variety of branch forms, different foliage shapes and colors, longevity, and natural, historic and cultural values. All of these elements provided by the oaks, combined with peace and quiet, and wildlife diversity, are much appreciated by visitors. The oak woods should reflect the terrain scale and can be used in the perception of certain spaces. Diversity can be achieved with different oak structures and ages or by combining oak with other formations and spaces. In turn, the visual power and scale can be used to provide a landscape unit, balancing colors, textures and shapes. The oak can also improve the design of existing forest patches, improving contours and colors, or promoting the stability and protection of forest areas. A proper selection allows increasing the recreational function of the oaks. Each wood has its own individual character. Aspects such as the location, nature, diversity, scale and size are taken into account and determine their interest. Larger areas have best advantages and allow more activities. But even small forests can be of great interest, particularly in regions where the territory was very modified by man. The natural diversification process is interesting in long-established woods. It is essential to identify the characteristics of a given oak forest, and make them accessible (Irving, 1985). Trails should allow access to different points of interest. Different recreational opportunities can be created for the public depending on the location, space and access. Generally, larger areas are better able to accommodate a greater number of visitors without significant disturbance. Smaller oak woods are best suited for casual uses. With good planning it is possible to reconcile the needs of those seeking peace and quiet with those who seek more specialized activities. Some spaces should allow visitors a longer stay and greater satisfaction. Particular attention should be given to security measures, such as wells, caves, large trees. In public areas, care should be taken with large and old trees because of the damages hazard. It is the responsibility of the owner and manager ensure good physical and health condition of these trees, removing those trees or branches at risk in public places, or seal their access. In certain

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locations, particular monitoring and maintenance measures may be needed in order to provide safety spaces for visitors. The existence of monumental or large trees, for example, may require special care to avoid unexpected situations or damages from visitors. Oak woods for conservation without interventions can become difficult to access for recreation. It is important to reconcile the different uses and plan for the long term. A great impact occurs when clearcuttings are applied thus an appropriate silvicultural system and harvesting planning is needed. The regeneration is one of the most important issues, since their presence may be not perpetual. It is important to ensure that new trees are established in a convenient way and ensure their survival and good growth. The importance of a given oak forest depends on their location. It increases on slopes because its form and structure become more visible. In flat areas, certain hills can also be exploited to give an attractive view. In certain regions, landscape and recreational aspects are considered more prevailing and decisive in the forest management.

Figure 19. Landscape dominated by oak forests with high conservation, aesthetics and recreational values.

In suburban surroundings, the oak woods may contribute to different recreation activities. In addition to aesthetics, may be important for conservation, education, improving the environment by absorbing air pollution and improving the local climate. Given its characteristics, often face reconstitution difficulties. Sometimes they are subject to human pressure and vandalism making difficult its maintenance and perpetuation. The silvicultural practices aim to maintain the vitality and stability of trees, their regeneration and perpetuation. The management of oak forests and the forestry operations should consider certain aspects such as: -

Reflect the shape of the terrain. Minimize intrusive effects. Enhance the visual importance of particular landforms (e.g, ravines, cliffs). Avoid artificial straight lines, regularities, patterns and geometric shapes. Scale properly with the ground. Integrate visually adjacent farmlands and create irregularities along the streams. Increase the diversity, structure and composition of certain stands.

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Other considerations can be mentioned: -

-

-

-

-

Trees size: there is a greater preference for larger trees in the landscape and recreational enjoyment (sense of permanence, architectural interest, historical reasons). Diversity, structure and composition: it is always preferable a certain varied diversity, structure and composition. Even in areas where they dominate as pure stands, the irregular shape of the crowns, trunks and branches, and the seasonal color of its leaves provide a great diversity and landscape interest. Location: oak woods may have more or less landscape interest depending on its position in a particular region. Its importance increases in mountainous and hilly situations because its structure, composition and shape become more visible. In flat areas, certain small elevations can play an important attractive role. On the other hand, one should also assess the geographical importance of certain spots; in some less wooded areas, the loss of any stand has much more impact than in high forested regions. Status: the status created in certain areas (Parks and Nature Reserves, Protected Landscape Areas), increases the scenic and recreation value of oak woods, attracting visitors; creates and increases the sense of its importance. Classification: the classification and identification of landscape and recreational areas are of special interest.

Silviculture practices include the following interventions:

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-

-

-

Stands not fully subject to cultural treatments, although justified for conservation reasons, may become inaccessible and impenetrable for recreation. On the other hand, stands too much intervention may no longer be attractive. Usually, the confrontation lies in defining how to keep its natural state while ensure, when possible, the productivity and sustainability. Operate in the long-term. Avoid extensive clearcuts, although in some cases the opening of logging gaps open new views. Regeneration: promoting natural regeneration. Control and protect the regeneration in the early stages from visitors and animals, using treeshelters, temporary fencing and warnings. Give special attention to old-growth forests. Consider the possibility of a positive non-intervention in some stands. In areas of greatest public interest, ensure the health and stability of mature trees, and protect historic and monumental trees.

8.4.1. Monumental Oak Trees Monumental trees are a precious part of our past, a living witness of our history. They have great aesthetic, biological, ecological, historical and cultural value. A large tree is also a component of our picturesque landscape, and illustrates the previous land use. Ancient oaks as well old-growth groves are of inestimable value. They have provided refuge and habitat for a wide variety of animals and plants for decades or centuries, while the landscape around them was changing. Our ancestors gave great value to ancient oaks, and

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have important symbolic, religious and social significance. Nowadays, veteran trees are a tourist attraction of great interest. Many of these giants are landmarks, and have a connection with some historic event. Several elements can be used for the recognition of such trees and woodlands. They are monumental trees for their size and age, and their biological, cultural and aesthetic interest. In addition to the considerable age and diameter, the oaks have a monumental set of features as long branches, dead branches, cavities in the trunk, fungal fruiting bodies or epiphytic plants. During his lifetime, an oak tree passes through various development stages (growth, maturity, regression). The genetic characteristics and the environment act by modifying the development expression of each tree. When young, the tree has a relatively homogeneous and functional architecture. As it grows the tree multiply the architectural reiterations. During this formative stage, there is a fast increase in size until it reaches maturity. At this stage, an optimal crown development is obtained. With increasing age there is a gradual crown reduction, its regression and reiterations, and a decreasing growth rate. The senescence is accompanied by a gradual decline in the vitality of the tree, their retrenchment and ultimately leads to his death. Ancient oaks are an important part of our heritage, and require care in order to persist. Their protection is of great importance. Monumental oaks can be found in different situations, and for its assessment and management should be considered its own individual characteristics and site conditions. It is important to guarantee a continuous management, extending its life, reconciling various uses and valuate its presence. Some oaks were pollarded in the past and still live, with dead branches, trunk cavities and other features, which shows its high resistance to decay and longevity. In many situations the best decision is carrying out any intervention, ensuring its stability and good growing conditions. Precipitate interventions can be harmful (e.g. excessive pruning). The space surrounding the tree should be managed, too. The soil conditions, the surrounding vegetation and external influences may affect the tree and its growth. The extensive grazing can reduce the effects of competing vegetation but if excessive can cause soil compaction and damage the roots. Measures to reduce firehazard are necessary. Soil mobilization near the tree must be avoided to not damaging the roots. The removal of other neighbor trees should be done cautiously and gradually. Other aspects are related to storms, and the presence of dead wood. Particular care should be taken in public areas. In the Appendix 1 are listed some monumental oak trees, which for their size, age or condition, worth our admiration, contemplation, respect, care and safeguarding. Some species such as Q. dunnii (Syn: Quercus chrysolepis var. palmeri) and Q. mohriana are small tree or shrub oaks. These monumental oaks are survivors of the past, keep old histories, and are an element of inspiration.

8.5. Oak Forest Management and Certification Oaks are a precious resource and its value can not just be measured in wood cubic meters. Currently, the aim is also an appreciation of its environmental and ecological functions. Besides wood production, silviculture must also consider other products and services such as edible mushrooms, hunting, wildlife conservation, water quality, recreation and landscape.

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The oak woods occupy a unique position in the landscape. Besides their characteristics and heritage, represents the natural forest of many territories and their characteristics. Oak woods are important from economic, ecological and cultural matters. The concept of sustainability linked to the oak forests aims to maintain and increase their areas, and its management for the production of various wood and non-wood products, biodiversity conservation, soil and water conservation, climate regulation, and natural landscape conservation. Many oak species if properly managed for quality wood may provide greater monetary value, allowing good economic returns, an interesting aspect in the maintenance of these systems by private owners. Given its characteristics, the oak forests allow the optimization of all of these ecological, social and productive functions. The forest certification is an important aspect, as it will enable and ensure a proper management. Certification of sustainable forest management has become important in forestry. The aim is to encourage and ensure the quality of forests and their management following the principles of sustainable development, in both its productive, environmental and social perspectives. It also intends to raise awareness and consumers attention to the relationship between industry and the environment, modifying behaviors. In this sense, the scope of sustainable forest management rests in large part to society and consumers, to require or give preference to products from sustainable oak forests. The sustainable management assumes that the different interventions, having a direct or indirect effect on the ecosystem, do not lead to irreversible processes. This requires a longterm maintenance of its structure and soil fertility, biodiversity conservation ensuring the ecosystem restoration and its functioning. The concept of sustainability on the oaks aims to maintain and increase their areas, and its management so as to produce various wood and non-wood products, conserve the biological diversity, provide the conservation of soil and water, conserve the natural landscape and mitigate climate changes. The management of many oak forests, in a much humanized environment, has been oriented to the economic use of their wood products. In many areas, we can assist to a worrying weakness of forests, resulting from pollution, drought and incidence of forest fires and forest overexploitation, among others. On the other hand, there is a growing concern about the conservation of forest biodiversity and demand for social use and landscape. Because of that, the sustainable management of oaks has received great attention in recent years, as a result of economic, social and environmental concerns and challenges. International commitments have been made to improve sustainable forest management, the protection of forests and the environment in general, approaching the concept of sustainable development (Lanly, 1999). Sustainable forest management was emphasized in the Statement of Forest Principles and Agenda 21 adopted at the United Nations Conference on Environment and Development held in Rio de Janeiro in 1992. In addition to common global problems, there are also more specific issues such as forest fires, desertification or under-use of potentialities. The guidelines for sustainable forest management are: optimize the production of wood and non-wood products; conserve biological diversity, genetic resources and aesthetic values; maintenance of forest formations in good growing and healthy conditions; ensure soil and landscape protection; ensure hydrological and biogeochemical cycle functions; maximize the climate regulation functions; meet economic, environmental and social objectives. In its general principles, the sustainable forest management of forests in Europe includes the following actions:

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Avoid human actions that lead to irreversible degradation of soil, flora and fauna, and the services that forests provide; Recognize that forestry is a long term activity; Encourage, in public and private lands, practices that promote sustainable management and multiple functions; Ensure the best combination of goods and services; Adequate protection of ecologically fragile areas and climax forests; Ensure the cultural heritage and landscape, water protection, erosion and flooding; Maintain and improve the stability, vitality, resistance and regeneration of forest ecosystems, including protection against destructive factors such as fires, pests and overgrazing; Encourage less artificial forestry practices; Give preference to native species and local ecotypes; Promote the production, use and marketing of forest products from sustainable managed forests.

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The requirements for a sustainable forest management consider an appropriate conduct, planning, execution and verification of management actions. The management activity should therefore follow a set of criteria and guidelines (Helsinki and Montreal Processes): Helsinki Process Criteria Maintenance and enhancement of forest resources and their contribution to carbon cycles. Maintenance of forest ecosystem health and vitality. Maintenance and encouragement of productive functions of forests (wood and nonwood). Maintenance, conservation and enhancement of biodiversity in forest ecosystems. Maintenance and enhancement of protective functions in forest management. Maintenance of other socio-economic functions and conditions. Montreal Process Criteria Conservation of biodiversity. Maintenance of productive capacity of forest ecosystems. Maintenance of forest ecosystem health and vitality. Conservation and maintenance of soil and water resources. Maintenance of forest contribution to global carbon cycles. Maintenance and enhancement of long term multiple socio-economic benefits to meet the needs of society.

In this context, the certification of a sustainable forest management has a particular relevance. It encourages the preservation of the environment, the adoption of appropriate forest management practices, appropriate working conditions and salaries. The certification of a forest management system is reflected in a document or certificate that assures to consumers the existence of a sustainable management plan followed by forest owners, managers, agencies and organizations. It also aims a better valuation of the products to the consumer (Barthod, 1996). The purposes of the forest management certification are to increase consumers awareness to the relationship between industry and the environment,

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increase consumers confidence, change the behavior of consumers, producers and industrials, enhance the environment quality and promote sustainable forest management (SAFC, 1995). Besides the regulations and organizations, the achievements of the sustainable forest management lie largely in the society and consumers, to the extent that they require or give preference to products from such kind of forests. Three important non-governmental organizations and initiatives of forest management certification are the Forest Stewardship Council (FSC), the Pan European Forest Certification (PEFC), and the International Organization for Standardization (ISO). These organizations use compatible principles and criteria. In terms of the management unit, the certification seeks to meet a number of aspects, such as the existing forest resources, provided products and services, biodiversity, protective functions, carbon storage, forest health and vitality, social and economic functions, and organizational structure. The oak forests allow the optimization of those ecological, social and productive functions, with great advantage in the development of sustainable forest management, and recognized value of its multiple functions. The certification of the oak management is therefore an important aspect, as it will enable a proper silviculture and of valuation of its products and services.

ACKNOWLEDGMENTS

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This work was partially funded by the following R&D projects: European research project AIR2-EC ‘Improvement of Mediterranean Oak Forests’ (1994-98); ‘Quality of Oak Forests and Technological Improvement’ supported by the Foundation for Science and Technology (1997-2000); ‘Valuation of Oak Forests’ by the National Institute of Agrarian Sciences, Portugal (2002-04).

CONCLUSION The oak forests provide high quality wood and are important in several aspects related with the environment protection, biodiversity conservation, aesthetics and recreation. Oak timber is valuated for its beauty, good mechanical properties and natural durability and may have multiple uses. Interest in both economic and ecological value of oaks will continue and probably increase in the future. Their relevance for multiple-purpose forest management as well high value timber supply is of great importance. Furthermore, oak woods have important historical and cultural values. The promotion of oaks multiple functions and the valuation of wood applications contribute to a proper forest management and the recovery of the ecosystem with socio-economic, environmental and ecological benefits. Through a proper forest management it is possible to obtain goods and services in a sustainable way that consider not only the socio-economic needs but also the conservation of the environment, the biodiversity and the ecosystem integrity. In order to pursue such benefits, different aspects need to be taken into consideration when planning the management of oak forests. In this chapter, diverse studies and management issues were referenced that allows the sustainability and improvement of oak forests.

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Lanly, J.-P. (1999). Aménagement forestier et gestion durable. Rev. For. Fra. nsp, 45-49. Larson, P. (1969). Wood formation and the concept of wood quality. Yale Univ., Bulletin 74. Léouffre, M-C. (1991). Effet du pâturage caprin sur la dynamique de production fourragère de taillis de chêne en région méditerranéenne française – Eléments pour une gestion pastirale. INRA. Avignon. Marchal, R. and Mothe, F. (1992). Appréciation des différentes classes des bois de chêne par le consommateur français. In: Proceedings Journée Profes. Bois, Clunny, France, 20 pp. Marren, P. (1992). The wild woods. David and Charles, London. Matić, S.; Prpić, B., Rauš, D.; Vranković, A. and Seletković, Z. (1979). Ekološko-uzgojne osobine specijalnih rezervata šumske vegetacije Prašnik I Muski Bunar u Slavoniji. In: II Kongres ekologa Jugoslavije, knj. I. Zagreb, 767-819. Mazet, J.-F. and Janin, G. (1989). Recherche des critères pour l’aspect (dessin et couleur) des placages de bois de Chêne. Cahiers Analyse Données 14, 365-376. McNaught, S. AND Wolf, L. (1984). General Ecology. Holt, Rinehart and Winston, 278 pp. McPhail, D. (1993). Woodlands and wildlife management. Forestry and British Timber Sept, 21 - 24. McShea, W. J. (2000). The influence of acorn crops on annual variation in rodent and bird populations. Ecology 81, 228-238. Meadows, J. and Goelz, J. (1998). First-year growth and bole quality responses to thinning in a red oak-sweetgum stand on a minor streambottom site. Ed. Thomas Waldrop. In: Proceedings Ninth biennial southern silvicultural research conference, Clemson, USDA, 188-193. Myers, C.A. (1971). Field and computer procedures for managed-stand yield tables. USDA For Serv Res Pap 79, Fort Collins, Colorado. Myers, N. (1990). The biodiversity challenge : expanded hot-spots analysis. The Environmentalist 10, 243-256. Nepveu, G. (1984). Déterminisme génotypique de la structure anatomique du bois chez Quercus robur. Silvae Genetica 33, 91-95. Nepveu, G. (1993). The possible status of wood quality in oak breeding programs (Quercus petraea Liebl, Quercus robur L.). Annales Sciences Forestier 80, 388-394. Odum, E. (1971). Fundamentals of Ecology. Philadelphia Saunders Company, pp. 927. Oliver, C. and Larson, B. (1990). Forest stand dynamics. McGraw-Hill, New York. Peterken, W. (1977). General management principles for nature conservation in British woodlands. Forestry 50, 27 - 48. Quézel, P. (1976). Le dynamisme de la végétation méditerranéen. Collana Verde 39 : 375391. Rego, F.; Castro, M. and Torres, F., (N.A.). Prescribed fire as a management tool in portuguese oak forests. ISA, Lisbon. Richards, F.J. (1959). A flexible growth function for empirical use. J. Exp.Bot. 10(29), 290300. SAFC (1995). Forest certification. Journal of Forestry 93, 6-10. Salas, F. AND Chuvieco, E. (1992). Dónde arderá el bosque? Previsión de incendios forestales mediante un SIG. In: Los Sistemas de Información Geográfica en la Gestión Territorial, Madrid, AESIGYT, 430-446. Salinger, M. (1981). Palaeoclimates north and south. Nature 291, 106-107.

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Oak Forest Management

Savil, P. (1986). Anatomical characters in the wood of oak (Quercus robur L. and Quercus petraea Liebl.) which predispose trees to shake. Commonweal Forest Revue 65, 109-116. Sevin, E. (1996). Différent modes de silviculture pour les chênes rouvre et pédonculé. Fôret enterprise 111, 18-20. Silva, I. AND Ruas, L. (1988). O uso do fogo controlado no norte de Portugal. In: Simpósio A Floresta e o Ordenamento do Espaço de Montanha. UTAD – SPCF, 26 – 29 Maio, Vila Real, 10 pp. Smith, D.M.; Larson, B.C.; Kelty, M.J. and Ashton, P.M. (1996). The Practice of Silviculture – Applied Forest Ecology. John Wiley and Sons, New York. Stephens, S.; Koons, D.; Rotella, J. AND Willey, D. (2003). Effects of habitat fragmentation on avian nesting success: a review of the evidence at multiple spatial scales. Biological Conservation 115: 101-110. Tarrega, R.; Luis, E.; Calvo, L. AND Marcos, E. (1991). Post-fire dynamics in Quercus pyrenaica ecosystems: possibilities of management. In: IV Congrés International des Terres Parcours, Montpellier, France, 159-161. Thibaut, B. (1993). La valorisation des bois de petit diamètre. Fôret enterprise 92, 32-37. Thomas, G. (1983). Trees in the landscape. Jonathan Cape Ltd, London. Valette, J-C.; Clément, A. AND Delabraze, P. (1979). Inflamabilité d’espéces méditerranéennes. INRA, Avignon. Van de Knap, W. O & Van Leeuwen, J. F. N., 1994. Holocene vegetation, human impact and climate change in the Serra da Estrela, Portugal. In: Lotter & Ammann (Eds.): Festschrift Gerhard Lang. Diis. Bot. 234, 497-535. Vanclay, J. (1989). A growth model for north Queensland rainforests. For. Ecol. Manag. 27, 245-271. Warren, M.S. and Fuller, R. J. (1993). Woodland rides and glades: their management for wildlife. Nature Conservation, Peterborough. Zeide, B. (1997). What kind of bricks should we use to build growth models: physiological or ecological?. In: Empirical and Process-based Models for Forest Tree and Stand Growth Simulation, Workshop, Oeiras (Portugal), Sept., 8 pp.

APPENDIX 1 Monumental Oak Trees Species Q. affinis Q. alba

Location Mexico, Pachuca, Hidalgo USA, Clay, IN

Q. alba ‘Wye Oak’

USA, Wye Mills, MD

Q. agrifolia

USA, Julian, CA

Q. bicolor

USA, Warm Springs, VA

Dimensions G: 4.0 m

Age aprox. (years) ---

G: 8.0 m CD: 42.1 m H: 33.5 m G: 9.7 m CD: 36 m H: 29 m G: 8.6 m CD: 22.9 m H: 17.7 m G: 7.5 m CD: 14.9 m H: 20.7 m

---

460 (died in 2002) ---

---

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João P. F. Carvalho (Continued) Species Q. canariensis Q. cerris Q. coccínea

Location France, Anduze, Gard Heligan Gardens, England USA, McCormick, SC

Q. copeyensis

Costa Rica

Q. crysolepsis

USA, Mendocino, CA

Dimensions G: 6 m

Age aprox. (years) ---

G: 5.7 m --G: 5.2 m CD: 27.4 m H: 40.6 m G: 10 m

---

---

Q. douglasii

Q. dunnii

Q. engelmanii

Q. faginea

Q. faginea Q. faginea

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Q. falcata

Q. falcata

Q. fusiformis

Q. garryana

Q. glabrescens Q. ilex Q. gemelliflora Q. infectoria Q. kelloggii

USA, 3 Rivers, CA USA, Lockwood, CA USA, Pasadena, CA Portugal, Reguengo Grande - Odemira Portugal, Cercal Alentejo Spain, Guadalupe USA, Thomaston, GA USA, Upson, GA USA, Young County, TX USA, Douglas, OR Mexico, Oaxaca France, Grasse Indonesia, Bogor, Java Cyprus, Paphos USA, Tuolumne, CA

G: 9.5 m CD: 27.6 m H: 24 m G: 7.0 m CD: 25 m H: 34.2 m G: 2.2 m CD: 12.2 m H: 10.7 m G: 3.7 m CD: 32.3 m H: 25.6 m G: 3.6 m CD: 30 m H: 20 m G: 6.5 m

---

---

---

---

300

--G: 5 m --G: 7.8 m CD: 47.5 m H: 45.7 m G: 8.4 m CD: 46.3 m H: 37.5 m G: 9.2 m CD: 27.4 m H: 14.7 m G: 7.0 m CD: 19.8 m H: 28.4 m G: 6.5 m

---

---

---

---

--G: 5 m --G: 5.5 m --G: 7 m --G: 7.1 m CD: 23.8 m H: 27.8 m

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Oak Forest Management

Species Q. lyrata

Q. lyrata

USA, Lewiston, NC

Q. lobata ‘Valley Oak’

USA, Covelo, CA

Q. macrocarpa

USA, Parris, KY

Q. michauxii

Q. mohriana

Q. mongolica Q. muehlenbergii

Q. myrsinifolia Q. nigra

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Location USA, Southampton, VA

Q. pagoda

Q. palustris

Q. petraea ‘Quarry Oak’ Q. petraea Q. petraea Q. phellos

Q. pubescens Q. pubescens Q. pyrenaica

USA, Kent, MD USA, Guadalupe Mount., TX Japan, Nagano USA, Montgomery, KY Japan, Tokyo USA, Jones, MS USA, Perquimans, NC USA, Greene, IN England, Croft Castle, Herefordshire Scotland, Borders Spain, Villablino USA, Charlotte, NC France, Murs France, Revest-de-Bion Spain, Caceres

Dimensions G: 8.0 m CD: 31 m H: 33.2 m G: 6.3 m CD: 36.5 m H: 47.5 m G: 8.8 m CD: 30.2 m H: 49.7 m G: 8.0 m CD: 31.5 m H: 29.2 m G: 7.5 m CD: 31.4 m H: 32.2 m G: 0.9 m CD: 6.7 m H: 6.4 m G: 9.4 m

Age aprox. (years) ---

---

500

---

---

---

--G: 8.0 m CD: 28.1 m H: 33.5 m G: 6.0 m

---

--G: 7.3 m CD: 32.9 m H: 35.9 m G: 8.7 m CD: 38.4 m H: 36.5 m G: 7.2 m CD: 33.5 m H: 33.2 m G: 13 m H: 11 m

---

---

---

1000

G: 9.7 m --G: 8 m H: 25 m G: 8.1 m CD: 34.4 m H: 38.7 m G: 6.8 m H: 20 m G: 5.1 m H: 25 m G: 6 m

-----

550 400 ---

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João P. F. Carvalho (Continued)

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Species Q. pyrenaica

Location Portugal, Bragança

Q. pyrenaica (group of 14 oaks)

Portugal, Serra Estrela

Q. robur ‘Carvalho de Calvos’

Portugal, Calvos

Q. robur ‘Carvalha Presépio’

Portugal, Castro Daire

Dimensions G: 4.9 m CD: 20 m H: 16 m G:2.7 – 3.4 m CD: 6 – 19 m H: 9 – 16 m G: 7.4 m CW: 41 m H: 29 m G: 13.2 m H: 22 m

Q. robur ‘Carballa da Rocha’ Q. robur ‘Chêne Chapelle’

Spain, Limia - Ourense France, Allouville

G: 6.9 m H: 33 m G: 15 m H: 18 m

Q. robur

France, Concoret

G: 9.5 m H: 15 m

Q. robur ‘Kvill Oak’

Sweden, Rumskulla

Q. robur ‘Royal Oak’ Q. robur ‘Major Oak’

Denmark, Jaegerspris England, Nottinghamshire

G: 14.2 m CW: 21 m H: 14 m G: 14 m

Q. robur ‘Majesty Fredville Oak’ Q. robur ‘Bowthorpe Oak’ Q. robur ‘Billy Wilkins Oak’

England, Kent

Q. robur ‘Newland Oak’

England, Newland

G: 13.5 m

Q. robur

Ireland, Belvoir Park

G: 8 m

Q. robur ‘The Big Tree’

The Netherlands, Laren

G: 7.5 m H: 25 m

450

Q. robur ‘Liernu’

Belgium, Eghezée

G: 10.4 m H: 17 m

700 - 800

England, Lincolnshire England, Melbury

G: 10 m CW: 28 m H: 16 m G: 12.2 m CW: 22 m H: 20 m G: 12 m H: 12 m G: 11.7 m CW: 17 m H: 21 m

Age aprox. (years) 500

400

500

900 (fell in a storm 1987) 500 1200

800

800 – 1000 (died few years ago) --800 (500 according to Mitchell 1966) 500 - 600

500 - 600 750

750 – 1000 (fell in a storm 1955) 500 - 700

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Oak Forest Management Species Q. robur

Q. robur

Q. robur

Q. robur

Q. robur

Q. robur

Q. rotundifolia

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Q. rotundifolia

Location Germany, Erle - Raesfeld

Dimensions G: 12.2 m H: 11 m

Germany, Ivenach

G: 11.25 m CW: 29 m H: 35 m G: 7.5 m H: 23 m

Bulgaria, Stara Zagora Lithuania, Stelmuze, Zarasai

G: 9.5 m

Poland, Kielce

G: 13.5 m CW: 40 m H: 30 m G: 7.4 m H: 30 m

Poland, Bialowieza Spain, LaTerrona Portugal, Matas - Santarém

Q. rubra

USA, Monroe, NY

Q. shumardii

USA, Anna, IL

Q. suber

Q. texana

Q. velutina

Portugal, N.S.Povoa Meada Portalegre USA, Morehouse Parish, LA

Age aprox. (years) 1000 – 1200

830

---

600

---

---

G: 8.0 m --G: 4.0 m CD: 31 m H: 14 m G: 10.3 m CD: 31 m H: 24.4 m G: 8.4 m CD: 29.2 m H: 29.2 m G: 7.3 m CD: 25 m H: 18 m G: 7.3 m CD: 24.6 m H: 34.4 m

400

---

500

---

USA, Hartford, CT

G: 8.7 m CD: 30.7 m H: 24 m

---

Q. virginiana ‘Angel Oak’

USA, Charleston, SC

G: 7.7 m CD: 27 m H: 20 m

600

Q. virginiana

USA, Tammany Parish, LA

G: 11.9 m CD: 41.7 m H: 20.4 m

---

USA, Audubon Park, LA

G:10.7 m CD: 50 m H: 23 m

---

Q. virginiana

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João P. F. Carvalho (Continued) Species Q. virginiana ‘Seven Sisters Oak’

Location USA, Mandeville, LA

Q. wislizenii

USA, Stockton, CA

Dimensions G: 11.2 m CD: 40 m H: 17 m G: 6.4 m CD: 22.3 m H: 15.5 m

Age aprox. (years) ---

---

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G – Girth at breast height (m); CD – Crown Width (m); H – Tree height (m).

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In: Oak: Ecology, Types and Management Editors: C. Aleixo Chuteira and A. Bispo Grão

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Chapter 2

INFLUENCE OF OAK BARREL AGING ON THE QUALITY OF RED WINES Pilar Rubio-Bretón1, Cándida Lorenzo2, M. Rosario Salinas2, Juana Martínez1, and Teresa Garde-Cerdán1,2

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1

Servicio de Investigación y Desarrollo Tecnológico Agroalimentario (CIDA). Instituto de Ciencias de la Vid y del Vino (Gobierno de La Rioja-CSIC-Universidad de La Rioja), Logroño, Spain 2 Cátedra de Química Agrícola. E.T.S.I. Agrónomos. Universidad de Castilla-La Mancha. Campus Universitario, Albacete, Spain

ABSTRACT Winemaking is a process involving several stages, with the barrel aging period having great importance in red wine quality. Wine in contact with oak wood undergoes important changes due to the contribution of numerous components characteristic of oak, mainly aromatic and polyphenolic compounds. Moreover, wood is a porous material that allows wine micro-oxygenation, so the barrel favors a series of chemical processes of oxidative type, which affect the polyphenolic content. During barrel aging, the wine increases its aromatic complexity and improves its stability, both of which increase its organoleptic quality. The extraction process of volatile and polyphenol compounds that takes place in oak barrels is very complex and depends on many factors, among which stand out: wood composition (related to the species and origin of the oak, the cooperage and the use of the barrels), the wine composition and the contact time between wine and wood. Moreover, a very important aspect is the age of the barrel, since ethylphenols can be formed as a consequence of the accumulation of undesirable microorganisms on wood, especially Brettanomyces/Dekkera. These ethylphenols are compounds with very unpleasant smells that negatively affect the sensory quality of wines. Furthermore, the repeated use of barrels plugs up the wood pores with the consequent reduction in micro-

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Pilar Rubio-Bretón, Cándida Lorenzo, M. Rosario Salinas et al. oxygenation. Barrel aging is a slow process, with a high economic cost that affects the final price of wines. For this reason, alternative techniques have emerged, faster and less expensive, such as the use of oak chips. Nowadays, there is a wide range of products available (types of oak, toasting, size, etc.) and different possibilities regarding the timing of oak chips addition, contact time, dose, application of micro-oxygenation jointly with this addition, etc. Depending on the type of wine to be obtained, these factors can be optimized to achieve the most quality wines. However, it should be noted that with the accelerated aging methods, quality wines can be obtained but the results provided by the barrel can be difficult to achieve. Therefore, in this chapter we have compiled the studies carried out to now on the aspects that can best influence the quality of aged wine. For this reason, this chapter is structured as follows: first we study the oak composition and the cooperage. Secondly, we discuss the influence of different parameters, such as the type of barrel (origin and oak species), the number of barrel uses or the wood-wine contact time, on the quality of this kind of wines. Next, we study the formation of ethylphenols in wines aged in oak barrels. And finally, we discuss the different aspects related to the use of new technologies for the aging of wine.

Keywords: Oak, Barrel, Aging, Volatile and phenolic compounds, Organoleptic quality, Ethylphenols, Chips, Micro-oxygenation

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INTRODUCTION References about the use of wooden containers for wine transport and storage exist since Roman ages. Over years, different woods have been used (chestnut, cherry, acacia, ash ...), but the oak was imposed due to its abundance in European forests and its high resistance [1]. Afterwards, it was shown that its physical and mechanical properties, and the chemical composition of this wood type were best suitable for aging wines. Wood is not an inert material, and therefore, the barrel aging leads to significant changes in wine composition which allow to improve organoleptic characteristics and to increase stability [2-4]. This aging process can be considered an essential step for further refinement in the bottle, in which the wine continues evolving until it reaches its fullness. The phenomena responsible for mainly transformations occurring in wines are: spontaneous clarification, due to the bitartrates and polyphenols precipitate-on, diffusion of oxygen through the wood and transfer of different compounds from oak to wine, like aroma and polyphenolic substances. The barrel aging can enhance the quality of certain wines, but not all wines are suitable for this complex process, requiring specific characteristics in terms of alcohol content, total acidity and phenolic balance [5-7]. The duration of aging should be adjusted to the personality and characteristics of each wine, so that the wood is not masked they [8-10]. During the maturation of wines in oak barrels, slow oxidation takes place. This leads to change the polyphenolic composition, which increase stability and improve organoleptic characteristics. Oxygen penetration in barrels depends on the oak type, environmental conditions of the winery, thickness of the staves, type of closing, and age and capacity of barrels. Among polyphenolic changes that wine undergoes during barrel aging can include the following: anthocyanins degradation [11, 12], tannins polymerization, anthocyanins and tannins combination [13], formation of new pigments [14], and transfer of polyphenols from wood.

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Influence of Oak Barrel Aging on the Quality of Red Wines

61

The extraction of aroma components from oak wood by the wine is fundamental and it contributes to the richness and complexity of aromas and taste. On the other hand, the wine aroma composition also evolves over time, diminishing the typical fruity aromas in young wines. The barrel aging enhances the organoleptic quality of wine, the color slightly evolves to yellow tonality, the intensity and complexity of aroma increases, improving its structure in the mouth and it becomes more smooth and balanced. In these sensory transformations the characteristics of the barrels play an important role, being oak species and origin, and toasting degree the factors mainly affecting the wine characteristics. Therefore, it is essential to choose the barrel so that the organoleptic impact and inducing oxidative phenomena are consistent with the development and enhancement of the specific characteristics of wine. Other factor to consider is barrel age, since the contribution of volatile substances and ellagic tannins decreases markedly with its continued use [15, 16]. In this sense, after 5 years, the contribution of the barrels is almost zero [17]. The pores of the wood undergo gradual plugging up, so the more the barrel age, the less oxygen penetration and therefore polyphenol oxidation [12]. In addition, the employment of used barrels involves certain risk because of microorganisms accumulate in the barrel surface, which can cause alterations in wine. The appearance of aromas such as leather, animal, horse sweat, phenol, etc. in wine is due to compounds produced by the action of Brettanomyces/Dekkera during the aging process. To avoid the development of these yeasts, hygiene is essential in wineries, and especially in used barrels [18, 19]. The environmental conditions of the winery play an important role during the aging process. Humidity and temperature influence on the precipitation reactions and mainly on the polyphenolic oxidation, as well as on the water and alcohol evaporation, and therefore, affect the decrease in volume that occurs in the barrels. If the wood-wine matching is poor, dominant “boisé” character may appear. So we must consider the choice of barrel and type of wine to age, being necessary to regulate properly the duration of aging. Each wine needs a different storage time; too much time remaining in barrel can oxidize and give table aroma to the wine. Actually, consumers demand balanced and complex wines, with slight wood aroma and fruity character. Mainly due to high cost and long periods of time that requires aging in barrels, new techniques have emerged in order to accelerate the process that involve this type of aging. In these techniques, the must or the wine is put in contact with oak wood chips during the elaboration or aging process. Moreover, in some cases, micro-oxygenation is used to complement the addition of oak chips into the wine in order to simulate the conditions of oxidation occurring during barrel aging. The aim of this chapter is to study the principal factors that affect the quality of wines aging in oak barrels. The chapter is structured as follows: Oak composition and cooperage. Influence of different parameters on the quality of barrel aged wine. o Volatile composition. o Phenolic composition. Sensory modifications in the wine. Incidence of ethylphenols in wine aged in oak barrels. New technologies for the aging of wine. Conclusion.

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Pilar Rubio-Bretón, Cándida Lorenzo, M. Rosario Salinas et al.

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OAK COMPOSITION AND COOPERAGE Oak belongs to Quercus genus, including more than 600 species. The crop spread over the Northern Hemisphere and it is widely distributed throughout Europe, North America, Central America, Southeast Asia, and to a lesser extent in the North Africa and South America. In Europe, the different species of oaks are divided into four subgenera. Quercus oersted (formerly Lepidobalanus) includes the two main European species used in the cooperage: Quercus petraea or sessilis and Quercus robur or pedunculata. These species are distributed throughout the European continent, although the main oak cooperage producer is France. Quercus petraea is grown mainly in central France (Allier, Argonne, Burgundy, Nevers, Vosges, ...) and Quercus robur is grown mostly in Limousin, a French region. The interaction of genetic, environmental and silvicultural factors is a trouble to assess the influence of oak species and geographical origin in the composition and properties of oak for cooperage [20]. A great variety of oak species are cultivated in the United States, but only the white oak species, especially Quercus alba, belonging to the subgenus Quercus oersted, are used for making barrels. This species is grown in the Eastern United States and it is usually identified by its origin: Missouri, Ohio, Illinois, Tennessee, Oregon, etc. In recent years, oaks from Eastern European countries (Hungary, Romania, Russia, Ukraine ...) have started to use in the cooperage industry. This is due to the high demand of barrels and thanks to political changes in this area. However, studies about these woods are scarce [21-23]. In Spain, there are also oaks in a small area of the North, and in recent years various studies have been done in order to characterize and determinate their oenological potential [24-30]. The results showed that Spanish oaks have characteristics intermediate between the American and French oaks, so they may be suitable for aging wines. An important parameter to considerer is growth rings. These are anatomical elements observed at first glance, and each one corresponds to one year in the life of the tree. Two different zones are within each annual ring (Figure 1): the spring wood, formed by thick vessels and thin cell walls, porous and light colored, and the summer wood, with smaller vessels and higher density [31, 32]. Growth rings

Summer woody small vessels

Spring wood

Spring woody big vessels

Summer wood

Dense fibrous zone Very dense fibrous zone

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Influence of Oak Barrel Aging on the Quality of Red Wines

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The width of annual rings in the cooperage is defined as grain, and oak species are assigned a grain type defined by their genetic fitness. Thus, Quercus petraea is considered of tight grain (1-3 mm), Quercus robur of wide grain (3-10 mm) and Quercus alba from tight to wide (1-5 mm). The wide grain oak has a high porosity and provides greater dry matter and ellagic tannins to the wines. The tight grain oaks, as Quercus sessilis, have denser wood and provide greater aromatic richness, hence are of higher quality for aging wines [33]. The oak chemical components can be divided into two groups [31, 34]: macromolecules and extractable fraction. The macromolecules are polymers of cellulose, hemicellulose and lignin, which constitute the cell wall and configure the physical and mechanical properties of wood, representing 90% of the mass of dry wood. The main components (in % of dry wood) are as follows:

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Polysaccharides (60-85%): cellulose (40-45%), and hemicellulose (20-35%). Lignin (15-35%). The extractable fraction represents about 10% of the mass of dry wood, and consists in soluble compounds (acids, lipids, phenolics, ellagitannins, etc.), which are variable depending on the species. They are not take part in the wood structure. Polyphenolic compounds are the most abundant, but there are other molecules such as aliphatic, terpenic, volatile, and furanic compounds; lactones, norisoprenoids, fatty acids, wax, etc., that make the classification complex. Wood composition is highly influenced by the oak species. French oak species have fewer differences between themselves than with American oak species. Many authors [20, 21, 33, 35-39] agree that American oak is characterized by a smaller amount of tannins than French oak, and high concentration of volatile compounds, mainly cis-oak lactone. The wood of Quercus robur has high content in extractable compounds and low in volatile compounds, while Quercus sessilis is richer in aromatic and poor in phenolic compounds [40]. In addition to the oak species, geographic origin and silvicultural treatments applied, the different processes from the wood is cut until the barrel is finished have also significant influence in the wood composition. The barrel manufacture is a complex process (Figure 2), as involve a first stage of selection of the wood, followed by the drying, shaping and toasting. To obtain the staves should be used straight trees, using only the lower trunk. First, the screening is done in the forest, using as selection criteria the good appearance [40]. The trunks are cut into pieces from which the staves are obtained by two different procedures: splitting and sawing. The choice of the cut process depends on the structure of wood, and especially on the abundance and thickness of the tyloses, cell membranes that clog the vessels of the spring wood. In the case of European oak, more porous because they have fewer tyloses, the wood is splitting, following the direction of medullary rays to ensure the tightness of the wood and to avoid the risk of leakage. In American oak, with less porous structure and abundance of tyloses [32], it is not necessary to follow the direction of medullary rays to ensure impermeability, so the wood is sawing, and the trunk is better utilized. The choice of cut technique affects the yield wood [42], and so it affects the final price of barrels. For this reason, barrels from European and American oak have different price. Green wood cannot be used for making barrels, as it contains 40-60% water and undesirable compounds for wine quality. Therefore, wood drying is essential before using for

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cooperage. This process can take place naturally, during 2-3 years in the open air; artificially, in an oven with humidity and temperature controlled; or both mixed, starting with drying in the open air for a short period (9-12 months) to finish in an oven [40, 43]. The natural season is affected by climatic factors (rain, wind, temperature, ...). Moreover, enzymatic and biochemical phenomena take place [44-46]. During the natural drying, the rain causes the decrease of ellagitannins [47], due to their high-water solubility, and their tendency to oxidation [45]. Artificial drying in an oven to moisture content around 15% can be achieved in a short time, but if it is done too quickly causes fast dehydration, that can lead to crack [46]. Natural drying favors the appearance of β-methyl-γ-octalactone from their precursors [48], and induces the isomerization to the cis form; contrary, artificial drying increases the trans form [40]. In artificial drying, the moisture reduction is not accompanied by changes due to microorganisms, so the staves have more quantity of ellagitannins and polyphenols and less quantity of vanillin, syringaldehyde and scopoletin, than in natural drying [49, 50]. Artificial drying has little influence on the ellagitannins content, but it decreases the levels of β-methyl-γ-octalactone, volatile phenols, fatty acids, and norisoprenoids [51]. The effect of drying type depends on the oak species [40, 50].

Figure 2. Diagram of barrel manufacture (from Jackson [41]).

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The shaping of the staves is the process by which the barrel adopts its characteristic form. For this process, the application of heat and humidity is required. Heat is applied through a live fire brazier, placed inside the cone formed by the staves, and held for 20 to 30 minutes, until the temperature inside of the staves is 200-220°C [1]. Then, second heating or toasting is applied, in order to shape the barrel, and to favor the formation of aroma substances. Toasting is one of the most influential operations in the oak composition, being its intensity and duration the main parameters in this process [52]. Depending on its duration, three principal types of toasting are defined: light, medium and heavy. The works of Chatonnet and Boidron [53] and Chatonnet et al. [54] established that the medium toasting is optimal for the synthesis of aroma compounds. During this step, many volatile compounds are formed with high organoleptic incidence in wines [52-56]. Toasting also influences the wood polyphenolic composition, and reduces the natural variability between oak species and origins [57]. Furanic aldehydes are formed from the wood polysaccharides by Maillard reaction [31]. According to the results obtained by Cadahía et al. [25], furanic aldehydes are the compounds that more increase during the toasting of the barrels, so these compounds have been proposed as an index of toasting. The thermal degradation of lignin leads to the formation of phenolic aldehydes (vanillin, syringaldehyde, coniferaldehyde, and synapaldehyde). The maximum concentration of these compounds was reached with medium toasting [54], being the most abundant syringaldehyde. Another group of compounds coming from the thermal degradation of lignin is the volatile phenols (guaiacol, 4-methylguaiacol, 4-ethylguaiacol, eugenol, isoeugenol, 4-vinylguaiacol, syringol, 4-methylsyringol, 4-allyl-syringol, etc.) [52, 54]; their concentration increases during the toasting process. The effect of toasting on eugenol is different depending on the species and origin of the oak [25]. Moreover, significant amounts of phenylketones are released from lignin heating: acetovanillone, propiovanillone, and butyrovanillone [54]. The content of β-methyl-γ-octalactone in oak wood increases by the effect of toasting, and the relationship between cis and trans isomers is not affected by this process [58]. The increase of these compounds during toasting is attributed to thermal degradation of the lipids present in oak. Its content increases with light and medium toasting, but decreases with heavy toasting [54]. Cadahía et al. [25] found that the effect of toasting on these lactones depends on the species and origin of the oak. During the toasting of the barrels is also produced the thermal degradation of the ellagitannins [56], and their decrease is between 72 and 99%, according to Matricard and Waterhouse [59]. This decrease is proportional to the toasting degree. As a result of the loss of ellagitannins, the wood astringency undergoes a significant decrease. The toasting process allows improving the aromatic impact of the oak wood, so its intensity should be adapted to the different oak species [52].

INFLUENCE OF DIFFERENT PARAMETERS ON THE QUALITY OF BARREL AGED WINE Volatile Composition Volatile compounds extracted from oak wood by wine and those formed during aging in barrels can be classified according to their chemical structure in furanic compounds, lactone

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compounds, phenolic aldehydes, and volatile phenols. The chemical structures of the principal oak volatile compounds are shown in Figure 3. The extraction of these compounds from oak and their subsequent transformations depend on several factors, including, the number of compounds initially present in wood (as discussed above), the contact time between wine and barrels, the number of barrel uses and the wine composition. All these compounds provide woody aroma though, if the maturation of wine in the barrel is successful, the smell of wood is not dominant and contributes to wine complexity. Furanic compounds are composed by furanic aldehydes (furfural, 5-methylfurfural, 5hydroxymethylfurfural), which are compounds extracted from wood to wine, and furanic alcohols (furfuryl alcohol, 5-methylfurfuryl alcohol, 5-hydroxymethylfurfuryl alcohol), formed from the chemical and/or biological reduction of the corresponding aldehydes, which takes place during wine maturation. All these compounds give to wine bitter almonds aroma, except 5-hydroxymethylfurfural that is practically odorless [60]. Their perception thresholds are shown in Table 1. Due to the perception thresholds of furanic aldehydes are high, it is believed that these compounds have not great importance in the wine aroma, although it seems that can enhance the flavor of the two isomers of oak lactones [67, 68]. Furfural is the most abundant and easily reducible [69], leading to furfuryl alcohol. Aroma of this late compound is like hay, and it has high perception threshold (Table 1). Its concentration is high in those wines that remain for long periods of time in barrel, because in this way, the time for reduction is higher.

Figure 3. Chemical structures of the principal oak volatile compounds. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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The group of lactone compounds includes the two isomers, cis- and trans- of the methyl- -octalactone (also called oak lactones). The cis-oak lactone shows lower perception threshold than trans-oak lactone and thus, it contributes more to the aroma of barrel aged wines [62, 64]. Their perception thresholds are shown in Table 1. When these compounds are present at low concentrations, they give to wine pleasant smell of wood, but high concentrations provide resin, varnish and coconut aromas, which are considered undesirable for wine aroma [15]. American oak gives to wine greater amount of cis-oak lactone while French oak gives higher quantity of trans-oak lactone. Thus, aroma potential of American oak is greater than that of French. The different concentrations of oak lactones between wines aged in American and French oak is maybe the most remarkable aroma differentiating feature among both types of wine [70-72]. Waterhouse and Towey [73] found that the relationship between cis- and trans-oak lactones is 6.0 1.3 in wines aged in American oak barrels and 1.3 0.2 in wines aged in French oak barrels. The principal phenolic aldehydes are vanillin and syringaldehyde. Vanillin, the main component of vanilla aroma, gives vanilla aroma to wines, and its perception threshold in red wines is 320 g/l (Table 1). The syringaldehyde has high perception threshold (Table 1), so its impact on wine aroma is low, but it can enhance the flavor of vanillin [74]. Within the group of volatile phenols are included eugenol, guaiacol, 4methylguaiacol, phenol, m-cresol, and p-cresol. Their perception thresholds are shown in Table 1. Eugenol gives to wine clove aroma; guaiacol and 4-methylguaiacol confer smoke and toast aroma; phenol gives smell of ink; and cresols give pharmaceutical aroma [61]. Table 1. Data of perception thresholds ( g/l), in red wines, of oak volatile compounds and ethylphenols

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Perception threshold

a

Furanic compounds Furfural 5-Methylfurfural 5-Hydroxymethylfurfural

20000a 45000a -

Phenolic aldehydes Vanillin Syringaldehyde

320a 50000a

Volatile phenols Eugenol Guaiacol 4-Methylguaiacol

500a 75a 65a

-Methyl- -octalactone cis Isomer trans Isomer

54b,c,d 370b,c,e

Ethylphenols 4-Ethylphenol 4-Ethylguaiacol

620f 140f

From Boidron et al. [61]; b From Brown et al. [62]; c From Spillman et al. [63]; d From Wilkinson et al. [64]; e From Günther and Mosandl [65]; f From Chatonnet et al. [66].

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Regarding to the effect of wine composition on the volatile compounds extraction from oak barrels, alcohol content of wine is the parameter that most affects the extraction of volatile compounds from oak wood. Maga [75] and Puech [76] found that synthetic wines with alcohol content of 40% and 55%, respectively, extracted greater amounts of oak lactones and phenolic aldehydes, respectively, from oak, than synthetic wines with low alcohol content. The accumulation of these compounds is more favored in wines with low alcoholic degree (12-12.5%) than in those with high alcoholic degree (13-13.5%). This may be because the extraction of volatile compounds is favored by higher alcohol content [77], but these compounds once extracted, can evolve in the wine [69, 78], and their evolution is more pronounced in wines with lower alcohol content. However, the pH and total acidity do not affect the extraction of volatile compounds from oak wood [79, 80]. In the other hand, the pool of oak extractives in a barrel is finite, so the number of barrel uses is another factor that determines the concentration of volatile compounds in aged wines. The extraction rate and amount of compounds extracted decrease with continued use of the barrels, as the barrels are depleted with their use [81-83]. The compounds which became more exhausted from barrel use are, in this order, furanic aldehydes, volatile phenols, phenolic aldehydes, and oak lactones [84, 85]. As for effect of aging time, the amount of compounds extracted by wine from oak is determined by the rate of release of these compounds from wood, and the rate at which these compounds are transformed by further chemical and/or biochemical reactions. The rate of the extraction, as seen in previous sections, depends mainly on wine and wood composition. Furanic aldehydes can be microbiologically reduced during aging to form the corresponding alcohols [69]. Furfural can also be transformed, chemically or microbiologically, in 2furanmethanethiol [86]. At the same time, the alcohols, formed from furanic aldehydes, of which furfuryl alcohol is the most important, can be transformed into the corresponding ethyl ether [69, 87]. For short aging, the extraction of these compounds is usually higher than their conversion, so they accumulate in wines, and their concentration increases. However, the conversion of furanic aldehydes into their corresponding alcohols is usually higher than the extraction when wines stay in barrels long time, so their concentration decreases [69, 88, 89]. The phenolic aldehydes can be also reduced to their corresponding alcohols [90]. Some studies have shown that concentration of phenolic aldehydes is maximal at 10-12 months of aging in oak barrels [76-78, 88]. The most important compound in terms of its contribution to wine aroma is vanillin. This compound, as happened with furanic aldehydes, is accumulated in wines when the aging period is short, while it decreases when increase the time of barrel aging [84, 85]. The volatile phenols are more stable than the above compounds, furanic and phenolic aldehydes, since they do not undergo chemical and/or microbiological transformations during aging of wine in barrels [84, 88]. Therefore, their concentration in wine mainly depends on the rate in which they are extracted. For example, Pérez-Prieto et al. [82] found that 4methylguaiacol needs 3 months to reach its maximum concentration, while guaiacol continues extracted for up to 9 months of aging. The oak lactones in wine are in equilibrium with their acidic and their corresponding ethyl ester [73]. As in volatile phenols, the oak lactones underwent small modifications in their concentration during the aging process [77, 89]. Therefore, the concentration of these compounds in wine depends on the extraction from the oak wood barrels.

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Phenolic Composition Polyphenols are a large group of compounds (8000 approximately) characterized by having an aromatic ring substituted by at least one hydroxyl [91]. They can be classified in non-flavonoids (phenolic acids and other compounds such as stilbenes and phenolic alcohols) and flavonoids (flavons, flavonols, anthocyanins and tannins). Grapes contain essentially nonflavonoids in the pulp and flavonoids in skin, seeds and scrapers. We can found these compounds in amounts ranging among 50-350 mg/l in white wines and 800-4000 mg/l in red ones [92]. These compounds are the principal responsible for some of the characteristics that defining the quality of wines, that is, color and its stability, flavour, bitterness and astringency; besides, several authors have studied their positive effect on human health. Moreover, phenolic compounds are essential for establishing the enological capacity of a wine for aging in oak barrels. In fact, a wine must have a minimum content of these compounds to be intended to aging in barrels. The content of these compounds in wines depends on both, their content in grapes and enological factors, such as time and temperature of maceration [93], micro-oxygenation [94], etc. In its turn, their content in grapes depends on many factors, agronomic (variety, age stock, vintage management, …) and climatic (time of sun exposition, rainfall, …). In addition, wine in contact with wood extract from it phenols [6, 95, 96], and this extraction depends also on the wine characteristics and on the barrel used (wood type, porosity, level of toasting, age of used, etc.) [97, 98]. During the wine maturation occur physical, chemical and physico-chemical processes, involving phenols from wine and barrel, which modify the wine characteristics [99, 100]. Many of these processes are reactions of oxidation, condensation, polymerization, and copigmentation which lead to color stabilization and softening astringency [12, 101]. The majority of these reactions occur due to oxygen passing through the pores of the wood and the staves [6, 102-104]. Figure 4 shows a scheme of these processes.

Figure 4. Scheme of changes occurring in wine during barrel aging (from Feuillat [105]). Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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The main phenolic compounds involved in the mentioned reactions are anthocyanins and tannins. Anthocyanins are responsible for the red and purple colors, but they are quite unstable, being influenced by pH and medium composition, and they are submitted to degradation, bleaching by SO2, complexation with metals, etc., which leads to color losses. However, their combination among themselves (self-associations), with tannins, or with other flavanols due to the reactions mentioned above, allows the formation of compounds more stables which can maintain the desirable color [106]. The oxidation of the anthocyanins leads to dismiss red color and to their combination with tannins, that increase stability and give red-purple tones. Moreover, tannin polymerization is produced and so increases the yellow color [107, 108]. Therefore during barrel aging the wine color evolves less vivid colors due to blue and yellow components of the color. These combinations and polymerizations are condensation reactions that can be mediated by acetaldehyde or not, and they will be responsible for color and astringency changes in wines [93, 109]. Tannins and anthocyanins condensations mediated by acetaldehyde give compounds with more purple colors and more color intensity than the anthocyanins from which they derive, their color is more stable against pH changes and they can only be partially decolorated by SO2. When there is enough acetaldehyde in the medium, they suffer polymerizations that give compounds with high molecular weight and purple color which precipitate [110, 111]. Copigmentation consists in molecular associations among anthocyanins, or between anthocianyns and other molecules called cofactors [101]. In young wines, copigmentation provides among 30 and 50% of their color [101]. However, this value is not so high in barrel aged wines, and there are different opinions about it. For example, according to some authors [106, 112], this value is between 14 and 22% for wines aged among 9 and 12 months. Nevertheless, Hermosín-Gutiérrez et al. [113] found this value among 0 and 5% for wines 9 months aged. These differences are probably due to the different grape varieties and winemaking processes in which are based the studies, and also, as some author suggest, it can be due to the copigmentation is the first step toward the formation of more stable polymeric pigments [101, 114, 115]. In this sense, Lorenzo et al. [106] obtained the following results: for young wines the percentage of copigmentation was between 29 and 37%, and the percentage of polimerization between 21 and 23%; but in aged wines the percentage of copigmentation decreased (14-20%) and the percentage of polimerization increased (3840%). In summarized, not only the initial content of phenolic compounds depends on several factors, as we have mentioned above, but also the reactions in which they are involved and the manner in which they are associated, will depend on all these factors (varietals, climatic, enological and related to the barrel used). And all these will influence in the final content of these compounds in a certain wine.

WINE SENSORY CHANGES DURING AGING During barrel aging the wine organoleptic characteristics evolve and change significantly, as result of numerous physical and chemical transformations that take place. The improvement in limpidness occurs due to precipitation of salts, polyphenols, colloids, etc., which take place while wine is in barrel, and it is favored by the small size of the barrel and

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by phenomena of adsorption on wood [12]. The color evolves significantly due to polyphenolic complex transformations that occur in the barrel, and the continuous microoxygenation that occurs through the wood. The color of a young red wine mainly depends on its concentration in anthocyanins, so red tones are predominant. During barrel aging, part of the anthocyanins is oxidized, resulting in a loss of red color. On the other hand, there are combinations of anthocyanins and tannins that increase the stability of color and red-violet tones provide. It also takes place the polymerization of tannins, with the consequent increase in yellow color. Thus, during barrel aging, red color evolves to less vivid tones, due to the increase in yellow and blue components. The aroma characteristics of wine are changed significantly due to compounds provided by oak, and wine reaches higher complexity [116]. In addition to primary or varietal aromas and secondary or fermentative aromas of wine, oak aromas are added during aging process, which predominant notes of: toasted, wood, coconut, spices, smoke, vanilla, almond, caramel, etc. The evolution of aromas of wood, smoke, and toasted in wine is closely linked to the oak origin and type of toasting applied to barrel [117]. The improved taste of wines in barrel is consequence of the contribution of typical oak compounds and polyphenolic changes that take place in wines. Phenolic compounds that wood gives to wine involve sensations of astringency and bitterness, and contribute to the increase of its structure and mouthfeel. Other substances given by oak wood, such as polysaccharides and sugars, contribute to the fat feeling of wine, and reduce significantly wine astringency [118]. The reduction of astringency [117] is due to anthocyanin-tannin combinations, the polymerization of the tannins by ethyl bonds and their complexation with polysaccharides. In addition, ellagitannins play an important role in stabilizing the color. For these reasons, aging in oak barrels enhances wine organoleptic quality, color slightly evolves to yellow tones, aroma increases in intensity and complexity, improving its structure in the mouth, and wine becomes more smooth and balanced. In these sensorial transformations play a fundamental role the characteristics of barrels, being species and origin of oak, and toasting degree the factors that more affect the wine characteristics. It is therefore essential to choose the barrel, in order to the impact organoleptic and oxidative phenomena occurring in the barrel are consistent with the development and improvement of wine specific characteristics. The results of sensory analysis of wine permit the classification of the oak in two defined groups: American and French oak [119-123]. In the other hand, Francis et al. [55] indicate that, although the geographic origin is an important variable that affects the wine sensory properties, toasting is the most important factor influencing the organoleptic characteristics that wood gives to wine.

INCIDENCE OF ETHYLPHENOLS IN WINE AGED IN OAK BARRELS Aroma is one of the most important characteristics in wine quality. Some volatile compounds contribute positively to wine aroma but other compounds may be negative due to the odor associated with them, and also to their ability for masking other positive compounds. This occurs with ethylphenols, 4-ethylphenol and 4-ethylguaiacol, which are negative

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compounds for wine quality, and they can cause great economic losses in the wine industry when consumers reject contaminated wines. Ethylphenols give an off-flavor described as phenolic, horse sweat, or stable odors [61, 66], if they are in the wine above a certain concentration (Table 1). The origin of these compounds is the sequential action of two enzymes (Figure 5) on a hydroxycinnamic acid (ferulic or p-coumaric acids) substrate [66].

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Figure 5. Biosynthesis of ethylphenols in wine by Brettanomyces/Dekkera sp. (From Chatonnet et al. [66]).

Hydroxycinnamate decarboxylase first turns these hydroxycinnamic acids in vinylphenols, which are then reduced to ethyl derivatives by vinylphenol reductase. The enzyme that facilitates decarboxylation is present in a large number of bacteria, fungi, and yeasts; however the reduction step is only performed by the species Dekkera bruxellensis, Dekkera anomala, Pichia guillermondii, Candida versatilis, Candida halophila and Candida mannitofaciens [18, 124-126]. The relationship between high concentrations of ethylphenols and activity of the yeast Brettanomyces/Dekkera in wines has been studied in recent years [127]. The formation of ethylphenols depends on both, their precursors and the population of contaminant Brettanomyces/Dekkera yeast. Moreover, their formation is favored in low alcoholic wines [77, 80, 128], as ethanol reduces microbiological activity slowing down the synthesis of these compounds. On the other hand, ethylphenols are formed in greater amounts in wines aged in barrels used than in new ones, and their concentration tend to increase throughout the aging time [79, 89]. The use of old barrels can favor the presence of Brettanomyces/Dekkera yeast, as these barrels are difficult to clean and sterilize. In addition, these yeasts grow slowly, which could explain the increase of ethylphenols concentration when the aging time increases. In addition, the ratio between 4-ethylphenol and 4ethylguaiacol found in wines can be a parameter dependent on the grape variety [80, 129]. In order to solve the problems associated to ethylphenols, we can act in preventive or curative way. du Toit et al. [130] studied the influence of O2 and SO2 on Brettanomyces development, and they found that it is important to reduce the O2 concentration and to maintain between 25 and 35 mg/l free SO2 to prevent their development. Also, Guzzon et al. [131] have studied the prevention of microbiological contamination in barrels using 4 different techniques: aqueous steam (100 ºC, 5-30 min), UV irradiation (36-W lamp, 5-30

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min), gaseous O3 (40 mg/m3, 30 min) and aqueous O3 (2 mg/l, 30 min). They found the most effective treatments those with aqueous steam and O3, which removing 70% of the yeast, and the less effective treatment was that with UV irradiation. However, Laureano et al. [132] showed that aqueous steam treatments are insufficient to eliminate yeasts and moulds entrapped in barrel staves. For all these reason, we can say that to prevent it is necessary microbiological control and using of sulphite and dimethyldicarbonate [133]. On the other hand, if ethylphenols and/or yeast are detected in wines, corrective action must be taken. Ugarte et al. [134] found that treating contaminated wine with two-part integrated process, involving a specific membrane and an adsorptive resin permit us to reduce ethylphenols concentration about 77% in wines. Moreover, Garde-Cerdán et al. [135] showed that the employment of a molecularly imprinted polymer would reduce the concentrations of 4ethylphenol and 4-ethyguaiacol about 90%, although it would also reduce the concentration of other important volatile compounds. A recent study try out the inactivation of contaminant yeast by applying low electric current (LEC) treatment [136], and the results showed that the growth of undesirable Dekkera can be inhibited by this treatment. The application of high pressure can also reduce the population of Brettanomyces bruxellensis in wines without causing important modifications in their physicochemical or sensory properties [137].

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NEW TECHNOLOGIES FOR THE AGING OF WINE The use of oak barrels is frequent in the production of wine quality. This involves high cost for wineries and long periods of time. Therefore, more economic techniques have emerged as the use of oak wood pieces in winemaking. This practice was included in the “International Code on Oenological Practices” by the International Organization of Vine and Wine (OIV) in 2001 (resolution OENO 9/2001 [138]). The requirements of oak wood chips used in this practice are regulated by the International Oenological Codex (resolution OENO 3/2005 [139]) which specifies the following: oak wood pieces must come exclusively for the Quercus genus, they can possibly be left in their natural state or they can be heated, they must not undergo any chemical, enzymatic or physical treatment other than heating, no compounds should be added to them and the dimensions of these particles must be such that at least 95% in weight be retained by the screen of 2 mm mesh. In the manufacture of alternative quality products is essential the selection of raw materials, controlled drying and proper cut or crushed. Furthermore, as in traditional cooperage, toasting is an essential step in obtaining alternative products. To toast wood chips or staves, some cooperages used roaster with rotary drum that use electricity, gas or infrared for heating the air inside the drum. This hot air toast the wood placed inside the drum by thermal convection. The heat penetrates and diffuses into the particles by thermal conduction, obtaining uniform toasted throughout the thickness of the fragments [140]. Other cooperages toast the wood with a flame of the same wood type before making the chips. In order to implement the new techniques of aging different products are marketed. Depending on their characteristics (botanical and geographical oak origin, chip size, type of toast, ...) and different possibilities of use (moment of application, time of contact with wine,

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doses, joint application of micro-oxygenation, ...), the results obtain in the wines will be variable, so it will be necessary to study all the factors to optimize their use. Regarding to the moment of use, oak alternative products can be used during winemaking (white or red wines) and/or during the storage of wines (in stainless steel tanks or used barrels). The use of oak chips during alcoholic fermentation of red wine improves the structure of the wine due to the contribution of polyphenolic compounds, which also stabilize the color by combining with anthocyanins [140]. Moreover, red wines fermented with chips are valued with the highest notes of fruit in the sensory evaluation. These wines were also the richest in ethyl esters of straight-chain, fatty acids and fusel alcohol acetates, compounds that play very important role on the perception of fruity notes [141]. As regards red wines that undergo malolactic fermentation with oak chips, it was observed that wood helps to reduce the intensity of the vegetative descriptor and increases red fruity and buttery descriptors with respect to the control wine in the sensory evaluation [142]. The fermentation of white musts in presence of oak chips is faster and the volatile compounds production is higher than the musts fermented without chips. This effect can be attributed to the action of the oak chips as a carrier for the yeast cells, exerting similar effect to that of immobilized cells [143]. Fermentation of white musts in presence of wood chips reduces vegetative aromas and increases astringency and bitterness due to ellagitannins and other compounds extracted from oak chips [144]. The addition of chips in white must before alcoholic fermentation give better sensory quality to wines than after the alcoholic fermentation. This is due to the best balance obtained between the varietal aromas and the aromas extracted from the wood during the alcoholic fermentation [145]. As in the cooperage, in the development of alternative products is also used wood from different geographical and botanical origins (see “Oak composition and cooperage” section). Wines treated with staves and chips of Spanish oak (Q. pyrenaica) showed similar volatile composition to those treated with French oak (Q. petraea) and American oak (Q. alba) [146]. Some authors observed that using French oak chips the aging of wine is slower than using American or Hungarian oak chips [147]. In the other hand, the toasting level of the wood is an important factor that affect to the wine quality. The unheated wood releases more hydrolysable ellagictannins, phenolic compounds that stabilize the red wine color and oxidize the excess of sulfur compounds, which are responsible for unpleasant odors. In addition, untoasted wood is less aromatic than toasted, allowing to improve mouthfeel as limit the aromatic impact. In addition, the toasting of wood increases the amount of vanillin, eugenol, guaiacol and its derivatives and furanic aldehydes (furfural and 5-methylfurfural), and decreases the concentration of the two isomers of oak lactones, probably due to its thermodegradation or less volatilization when the wood is subjected to high temperatures. This was observed by Guchu et al. [148] in a white wine treated with chips toasted and untoasted. Wines macerated with medium plus oak chips showed higher concentrations of volatile phenols than those treated with medium toast chips [149]. Moreover, the size of fragments influences the contact surface wine/wood. This should be taken into account to calculate the dose rate and contact time requested [150]. The sizes available are varied: powder, chips, cubes, shavings, granulates, dominoes, segments, staves, etc. (Figure 6). With smaller oak pieces, especially with fine shavings, the extraction of oak-derived flavor compounds is much faster due to the large surface area [151]. On the other hand, the

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behaviour of the staves is more similar to the behaviour of the barrels (slower diffusion kinetics than in the case of chips) [152], so it is easier to adjust the contact surface.

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Figure 6. Size fragments of oak wood used in alternative aging techniques.

Depending on the objectives, the contact time between the wood and the must or wine can vary from some days to several weeks or even months. This time will depend on the wood type, chip size and flavor and taste profile searched for the wine. The chips quickly give aroma compounds to wines, before their stabilization, and even decrease when the contact time exceeds 3 months. The wines aging in new oak extracted higher concentrations of aroma compounds and for longer periods than the wines with the addition of chips (both stored in tanks and in used barrels) [153]. The greatest contribution of volatile compounds (furfural, 5methylfurfural, oak lactones, 4-ethylphenol, 4-ethylguaiacol, eugenol, vanillin, isoeugenol, guaiacol, syringaldehyde, etc.) in wines with the addition of chips is reached during the first 15 or 30 days of contact between wood and wine, and then remaining constant for the most of the compounds. Some compounds may continue to increase slightly longer, or decreasing in the case of furfural and 5-methylfurfural due to the formation of furfuryl alcohol or 2furanmethanethiol [149, 154]. In addition, the dose of alternative products mainly depends on the fragment size. Usually, the dose is between 1 and 5 g/l and sometimes it is up to 20 g/l. With larger doses are obtained higher intensities of woody, coconut, vanilla, toasty and toffee descriptors in wines [150]. Currently, the combined application of micro-oxygenation with alternative oak products is used. The micro-oxygenation is the process by which oxygen is added to wine in a controlled way. The aim of micro-oxygenation is to stabilize red wine color and improve wine quality. The micro-oxygenation treatment can be carried out during alcoholic

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fermentation and after malolactic fermentation, but oxygen addition before malolactic fermentation provided the optimal results [155]. Another objective of the micro-oxygenation is to imitate the natural oxygenation that takes place in oak barrels. This technique can be used in stainless steel tanks with alternative wood products to simulate aging in oak barrels [156]. With the joint application of micro-oxygenation and alternative products, the obtained wine has greater color intensity, and ensures greater color stability (monomeric anthocyanins decrease and polymeric anthocyanins increase) [157]. At sensory level, the effects of microoxygenation are to reduce astringency and herbaceous aromas, to maintain fruity aroma, and to get more structured and complex wines.

CONCLUSION In a process so complex as described in this chapter, it is very difficult to generalize or draw conclusions. The barrel aging is not an exact science, since the factors involved in this process are many and complex, they are not independent and interact each other. Both wine and wood evolve over aging, so depending on the raw material (wine and barrel) and the wine we want to obtain, we should plan this process in one or another way. With the new accelerated aging techniques, quality wines may also be produced, but to avoid unfair competition with the traditional production, longer and more costly, the wines obtained using these new techniques should be differentiated, so the consumers can choose freely.

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ACKNOWLEDGMENTS P. R.-B. thanks to the Gobierno de La Rioja for the pre-doctoral grant. T. G.-C. thanks to the Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) and Gobierno de La Rioja for the DOC-INIA contract.

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[87] Vanderhaegen, B.; Neven, H.; Daenen, L.; Verstrepen, K.J.; Verachtert, H.; Derdelinckx, G. Furfuryl ethyl ether: important aging flavor and a new marker for the storage conditions of beer. J. Agric. Food Chem., 2004, 52, 1661-1668. [88] Jarauta, I.; Cacho, J.; Ferreira, V. Concurrent phenomena contributing to the formation of the aroma of wine during aging in oak wood: an analytical study. J. Agric. Food Chem., 2005, 53, 4166-4177. [89] Garde-Cerdán, T.; Ancín-Azpilicueta, C. Review of quality factors on wine ageing in oak barrels. Trends Food Sci. Technol., 2006, 17, 438-447. [90] Spillman, P.J.; Pollnitz, A.P.; Liacopoulos, D.; Skouroumounis, G.K.; Sefton, M.A. Accumulation of vanillin during barrel-ageing of white, red, and model wines. J. Agric. Food Chem., 1997, 45, 2584-2589. [91] Croteau, R.; Kuthchan, T.M.; Lewis, N.G. Natural products (secondary metabolism). In: Biochemistry and Molecular Biology of Plants. Rockville: American Society of Plants Physiologists; 2000; pp. 1250-1318. [92] Santos-Buelga, C. Últimos avances en el estudio de los compuestos fenólicos del vino. Semana Vitivinícola, 1997, 2671/72, 3847-3861. [93] Díaz-Plaza, E.M. Estudio de la capacidad de crianza de vinos monovarietales de Monastrell. Thesis. Universidad de Castilla-La Mancha, Spain. 2004. [94] Sánchez-Iglesias, M.; González-Sanjosé, M.L.; Pérez-Magariño, S.; Ortega-Heras, M.; González-Huerta, C. Effect of micro-oxygenation and wood type on the phenolic composition and color of an aged red wine. J. Agric. Food Chem., 2009, 57, 1149811509. [95] Fernández de Simón, B.; Hernández, T.; Cadahía; E.; Dueñas, M.; Estrella, I. Phenolic compounds in a Spanish red wine aged in barrels made of Spanish, French and American oak wood. Eur. Food Res. Technol., 2003, 216, 150-156. [96] Pérez-Magariño, S.; González-Sanjosé, M.L. Evolution of flavanols, anthocyanins, and their derivates during the aging of red wines elaborated from grapes harvested at different stages of ripening. J. Agric. Food Chem., 2004, 52, 1181-1189. [97] del Álamo, M.; de Castro, I.R.; Casado, L.; Nevares, I.; Cárcel, L.M. Influencia del tipo de barrica en el envejecimiento del vino tinto D.O. Cigales. Compuestos fenólicos y color. Vitic. Enol. Prof., 2002, 82, 41-48. [98] Ortega-Heras, M.; Pérez-Magariño, S.; Cano-Mozo, E.; González-Sanjosé, M.L. Differences in the phenolic composition and sensory profile between red wines aged in oak barrels and wines aged with oak chips. LWT-Food Sci. Technol., 2010, 43, 15331541. [99] Chatonnet, P. Influence des procédés de tonnellerie et des conditions d'élevage sur la composition et la qualité des vins élevés en fûts de chêne. Thesis. Université de Bordeaux II, France. 1995. [100] Vivas, N. La qualité du bois de chêne et son utilisation pour la vinification et l´elevage des vins. J. Sci. Tech. Tonnellerie, 1995, 1, 1-8. [101] Boulton, R.B. The copigmentation of anthocyanins and its role in the color of red wine: A critical review. Am. J. Enol. Vitic., 2001, 52, 67-87. [102] Revilla, I.; González-Sanjosé, M.L. Effect of different oak woods on aged wine color and anthocyanin composition. Eur. Food Res. Technol., 2001, 213, 281–285. [103] Wang, H.; Edgard, J.R.; Shrikhande, J. Anthocyanin transformation in Cabernet Sauvignon wine during aging. J. Agric. Food. Chem., 2003, 51, 7989–7994.

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[104] Mateus, N.; Oliveira, J.; Pissarra, J.; González-Paramás, A.M.; Rivas-Gonzalo, J.C.; Santos-Buelga, C.; Silva, A.M.S.; de Freitas, V. A new vinylpyranoanthocyanin pigment occurring in aged red wine. Food Chem., 2006, 97, 689–695. [105] Feuillat, F. Contribution à l’étude des phénomenes d’échanges bois-vin-atmosphère à l’aide d’un «fût» modele. Relations avec la estructure anatomique du bois de chêne (Quercus robur L. et Q. petraea Liebl.). Thesis. Université de Nancy, France. 1996. [106] Lorenzo, C.; Pardo, F.; Zalacain, A.; Alonso, G.L.; Salinas, M.R. Effect of red grapes co-winemaking in polyphenols and color of wines. J. Agric. Food Chem., 2005, 53, 7609-7616. [107] Gómez-Cordovés, C.; del Álamo, M.; Bernal, J.L. Envejecimiento de un vino tinto de Ribera del Duero: variaciones de los monosacáridos, familias fenólicas y color debidas al tipo de roble y tonelería de procedencia. Vitic. Enol. Prof., 2001, 72, 36-43. [108] Gómez-Cordovés, C.; González-Sanjosé, M.L. Interpretation of color variable during the aging of red wines: relationship with families of phenolic compounds. J. Agric. Food Chem., 1995, 43, 557-561. [109] Dueñas, M.; Fulcrand, H.; Cheyner, V. Formation of antocyanin flavanol adducts in model solutions. Anal. Chim. Acta, 2006, 563, 15-25. [110] Santos-Buelga, C.; Vivar-Quintana, A.; Francia-Aricha, M.T.; Escribano-Bailón, J.C.; Rivas-Gonzalo, J.C. Estabilidad de color en los vinos tintos. Interacciones entre compuestos y formación de nuevos pigmentos. In: Jornada Técnica de Enología. Aspectos Científicos y Técnicos del Color del Vino. Tarragona, Spain. 1998. [111] Revilla, I. Efecto de la aplicación de enzimas pectinolíticas, clarificantes y extractoras de color, sobre la calidad de vinos tintos. Thesis. Universidad de Burgos, Spain. 1999. [112] Darias-Martín, J.; Carrillo-López, M.; Echavarri, J.F.; Díaz-Romero, C. The magnitude of the copigmentation in the color of aged wines made in Canary Islands. Eur. Food Res. Tech., 2007, 224, 643-648. [113] Hermosín-Gutiérrez, I.; Sánchez-Palomo, E.; Vicario-Espinosa, A. Phenolic composition and magnitude of copigmentation in young and sortly aged red wines made from the cultivars Cabernet Sauvignon, Cencibel and Syrah. Food Chem., 2005, 92, 269-283. [114] Escribano-Bailón, T.; Dangles, O.; Brouillard, R. Coupling reactions between flavylium ions and catechin. Phytochemistry, 1996, 41, 1583-1592. [115] Santos-Buelga, C. Substancias polifenólicas y color del vino tinto. In: Mas A., editor, Enología avui. Tarragona, Spain: Facultat dÉnologia de Tarragona; 2001; pp. 29-37. [116] Aiken, J.W.; Noble, C. Composition and sensory properties of Cabernet sauvignon wine aged in French versus American oak barrels. Vitis, 1984, 23, 27-36. [117] Vivas, N.; Saint-Cricq de Gaulejac, N.; Doneche, B.; Glories, Y. Incidence de la durée du séchage naturel de Quercus petraea Libl. and Quercus robur L. sur la diversité de la flore fongique en place et sur quelques aspects de son écologie. J. Sci. Tech. Tonnellerie, 1997, 3, 17-25. [118] Vivas, N. Un état des connaissances sur le bois de tonnellerie et son utilisation. Rev. Oenol., 1997, 83, 7-10. [119] Jindra, J.A.; Gallander, J.F. Effect of American and French oak barrels on the phenolic composition and sensory quality of Seyval blanc wines. Am. J. Enol. Vitic., 1987, 38, 133-138.

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[120] Artajona, J. Caracterización del roble según su origen y grado de tostado mediante la utilización de GC y HPLC. Vitic. Enol. Prof., 1991, 14, 61-72. [121] Chatonnet, P.; Ricardo-da-Silva, J.M.; Dubourdieu, D. Influence de l’utilisation de barriques en chêne sessile européen (Quercus petrae) ou en chêne blanc américain (Quercus alba) sur la composition et la qualité des vins rouges. Rev. Fr. Oenol., 1997, 165, 44-48. [122] Martínez, J. Envejecimiento en barrica de roble de vinos tintos de Rioja. In: La Barrica como Factor de Calidad en la Crianza de los Vinos Tintos. Logroño, Spain: Gobierno de La Rioja; 1999; pp. 73-94. [123] Martínez J. Incidencia del Origen de la Madera de Roble en la Calidad de los Vinos de Tempranillo de la D.O.Ca. Rioja durante la Crianza en Barrica. Logroño: Gobierno de La Rioja. 2006. [124] Chatonnet, P.; Viala, C.; Dubourdieu, D. Influence of polyphenol components of red wines on the microbial synthesis of volatile phenols. Am. J. Enol. Vitic., 1997, 48, 443448. [125] Dias, L.; Dias, S.; Sancho, T.; Stender, H.; Querol, A.; Malfeito-Ferreira, M.; Loureiro, V. Identification of yeasts isolated from wine-related environments and capable of producing 4-ethylphenol. Food Microbiol., 2003, 20, 567-574. [126] Edlin, D.A.N.; Narbad, A.; Dickinson, J.R.; Lloyd, D. The biotransformation of simple phenolic compounds by Brettanomyces anomalus. FEMS Microbiol. Lett., 1995, 125, 311-316. [127] Suárez, R.; Suárez-Lepe, J.A.; Morata, A.; Calderón, F. The production of ethylphenols in wine by yeasts of the genera Brettanomyces and Dekkera: A review. Food Chem., 2007, 102, 10-21. [128] Dias, L.; Pereira-da-Silva, S.; Tavares, M.; Malfeito-Ferreira, M.; Loureiro, V. Factors affecting the production of 4-ethylphenol by the yeast Dekkera bruxellensis in enological conditions. Food Microbiol., 2003, 20, 377-384. [129] Pollnitz, A.P.; Pardon, K.H.; Sefton, M.A. Quantitative analysis of 4-ethylphenol and 4ethylguaiacol in red wines. J. Chromatogr. A, 2000, 874, 101-110. [130] du Toit, W.J.; Pretorius, I.S.; Lonvaud-Funel, A. The effect of sulphur dioxide and oxygen on the viability and culturability of a strain of Acetobacter pasteurianus and a strain of Brettanomyces bruxellensis isolated from wine. J. Appl. Microbiol., 2005, 98, 862-871. [131] Guzzon, R.; Widmann, G.; Malacarne, M.; Nardin, T.; Nicolini, G.; Larcher, R. Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. Eur. Food Res. Tech., 2011, 233, 285-291. [132] Laureano, P.; D’Antuono, I.; Malfeito-Ferreira, M.; Loureiro, V. Effect of different sanitation treatments on the numbers of total microorganisms and of Dekkera bruxellensis recovered from the wood of wine ageing barriques. In: Abstracts of the 23rd International Specialised Symposium on Yeasts. Budapest, Hungary. 2003. [133] Loureiro, V.; Malfeito-Ferreira, M. Spoilage yeasts in the wine industry. Int. J. Food Microbiol., 2003, 86, 23-50. [134] Ugarte, P.; Agosin, E.; Bordeu, E.; Villalobos, J.I. Reduction of 4-ethylphenol and 4ethylguaiacol concentration in red wines using reverse osmosis and adsorption. Am. J. Enol. Vitic., 2005, 56, 30-36.

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[135] Garde-Cerdán, T.; Zalacain, A.; Lorenzo, C.; Alonso, J.L.; Salinas, M.R. Molecularly imprinted polymer-assisted simple clean-up of 2,4,6-trichloroanisole and ethylphenols from aged red wines. Am. J. Enol. Vitic., 2008, 59, 396-400. [136] Lustrato, G.; Vigentini, I.; de Leonardis, A.; Alfano, G.; Tirelli, A.; Foschino, R.; Ranalli, G. Inactivation of wine spoilage yeasts Dekkera bruxellensis using low electric current treatment (LEC). J. Appl. Microbiol., 2010, 109, 594-604. [137] Puig, A.; Vilavella, M.; Daoudi, L.; Guamis, B.; Minguez, S. Microbiological and biochemical stabilization of wines by application of high pressure processing. Bull. O.I.V., 2003, 76, 596-617. [138] Resolution OENO 9/2001. Usage of pieces of oak wood in winemaking. Office International de la Vigne et du Vin. 2001. [139] Resolution OENO 3/2005. Pieces of oak wood. International Oenological Codex. 2005. [140] Chatonnet, P. Productos alternativos a la crianza en barrica de los vinos. Influencia de los parámetros de fabricación y de uso. Revista Enología, 2007, 4, 2-24. [141] Rodríguez-Bencomo, J.J.; Ortega-Heras, M.; Pérez-Magariño, S. Effect of alternative techniques to ageing on lees and use of non-toasted oak chips in alcoholic fermentation on the aromatic composition of red wine. Eur. Food Res. Technol., 2010, 230, 485-496. [142] Gutiérrez Afonso, V.L. Sensory descriptive analysis of red wines undergoing malolactic fermentation with oak chips. J. Food Sci., 2003, 68, 1075-1079. [143] Pérez-Coello, M.S.; Sánchez, M.A.; García, E.; González-Viñas, M.A.; Sanz, J.; Cabezudo, M.D. Fermentation of white wines in the presence of wood chips of American and French oak. J. Agric. Food Chem., 2000, 48, 885-889. [144] Gutiérrez Afonso, V.L. Sensory descriptive analysis between white wines fermented with oak chips and in barrels. J. Food Sci., 2002, 67, 2415-2419. [145] Martínez, J.; Ojeda, S.; Rubio, P. Aplicación de fragmentos de roble en la elaboración de vinos blancos. Incidencia sobre la composición y calidad sensorial. In: Avances en Ciencias y Técnicas Enológicas. Transferencia de Tecnología de la Red GIENOL al Sector Vitivinícola; 2007; pp. 289-291. [146] Fernández de Simón, B.; Cadahía, E.; Muiño, I.; del Álamo, M.; Nevares, I. Volatile composition of toasted oak chips and staves and of red wine aged with them. Am. J. Enol. Vitic., 2010, 61, 157-165. [147] del Alamo Sanza, M.; Nevares Domínguez, I. Wine aging in bottle from artificial systems (staves and chips) and oak woods: Anthocyanin composition. Anal. Chim. Acta, 2006, 563, 255-263. [148] Guchu, E.; Díaz-Maroto, M.C.; Pérez-Coello, M.S.; González-Viñas, M.A.; Cabezudo Ibáñez, M.D. Volatile composition and sensory characteristics of Chardonnay wines treated with American and Hungarian oak chips. Food Chem., 2006, 99, 350-359. [149] Rodríguez-Bencomo, J.J.; Ortega-Heras, M.; Pérez-Magariño, S.; González-Huerta, C. Volatile compounds of red wines macerated with Spanish, American, and French oak chips. J. Agric. Food Chem., 2009, 57, 6383-6391. [150] García-Carpintero, E.G.; Gómez Gallego, M.A.; Sánchez-Palomo, E.; González Viñas, M.A. Sensory descriptive analysis of Bobal red wines treated with oak chips at different stages of winemaking. Aust. J. Grape Wine Res., 2011, 17, 368-377. [151] Campbell, J.I.; Pollnitz, A.P.; Sefton, M.A; Herderich, M.J.; Pretorius, I.S. Factors affecting the influence of oak chips on wine flavour. Aust. New Zeal. Wine Ind. J., 2006, 21, 38–42.

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[152] Fernández de Simón, B.; Cadahía, E.; del Álamo, M.; Nevares, I. Effect of size, seasoning and toasting in the volatile compounds in toasted oak wood and in a red wine treated with them. Anal. Chim. Acta, 2010, 660, 211-220. [153] Bautista-Ortín, A.B.; Lencina, A.G.; Cano-López, M.; Pardo-Mínguez, F.; López-Roca, J.M.; Gómez-Plaza, E. The use of oak chips during the ageing of a red wine in stainless steel tanks or used barrels: Effect of the contact time and size of the oak chips on aroma compounds. Aust. J. Grape Wine Res., 2008, 14, 63-70. [154] Martínez, J.; Rubio, P.; Ojeda, S. Aplicación de chips en vinos tintos. Optimización del tiempo de contacto madera-vino In: Reuniones del Grupo de Trabajo de Experimentación en Viticultura y Enología: 22ª Reunión. Logroño, La Rioja, Spain: Ministerio de Agricultura, Pesca y Alimentación; 2007; pp. 51-60. [155] Cejudo-Bastante, M.J.; Hermosín-Gutiérrez, I.; Pérez-Coello, M.S. Micro-oxygenation and oak chip treatments of red wines: Effects on colour-related phenolics, volatile composition and sensory characteristics. Part I: Petit Verdot wines. Food Chem., 2011, 124, 727-737. [156] du Toit, W.J.; Marais, J.; Pretorius, I.S.; du Toit, M. Oxygen in must and wine: a review. South Afr. J. Enol. Vitic., 2006, 27, 76-94. [157] McCord, J. Application of toasted oak and micro-oxygenation to ageing of Cabernet Sauvignon wines. Aust. New Zeal. Grapegrower and Winemaker, 2003, 43-53.

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In: Oak: Ecology, Types and Management Editors: C. Aleixo Chuteira and A. Bispo Grão

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Chapter 3

DEHESAS: OPEN WOODLAND FORESTS OF QUERCUS IN SOUTHWESTERN SPAIN R. Alejano , J. Vázquez-Piqué, J. Domingo-Santos, M. Fernández, E. Andivia, D. Martín, C. Pérez-Carral and M. A. González-Pérez Agroforestry Sciences Department, University of Huelva, Huelva, Spain

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1. INTRODUCTION The Mediterranean basin provides a classical example of man’s interaction with his environment (Thirgood, 1981), and Spanish dehesas, an open woodland forest agroecosystem created and maintained by humans and their livestock, are a clear example of this interaction. These systems span an area of nearly 3.2 million ha in Spain (Junta de Andalucia, 2005), roughly 40% of which is in the region of Andalusia (southern Spain). They are mainly covered by trees of the genus Quercus, at a density of 20- 50 trees/ha, with an understorey of crops, grassland or shrubland where cattle, sheep, pigs and goats can be raised (San Miguel, 1994). Such systems require human intervention to maintain a balance between production and conservation. The area where dehesas are found has a Mediterranean climate, with irregular precipitation between and within years, and hot, dry summers. Given these conditions, most of the trees are sclerophyllous species, and have physiological adaptations and deep root systems (Ruiz de la Torre, 2006; Fernández et al., 2008a), allowing them to cope with harsh summers and occasional frosts in winter. Likewise, nutrient poor soils, mostly acid or neutral, and a smooth and undulating topography contribute to the existence of these systems, which, according to many authors, are the best agroforestry option for an environment with these ecologically limiting factors, and which, hence, has limited potential for production (Fernández and Porras, 1999).

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The main species in dehesas, covering more than 80% of their area, is Quercus ilex L. ssp. ballota [Desf.] Samp. (Holm Oak), followed by Quercus suber L. (Cork Oak). Nevertheless, these systems are not always single-species forests. Depending on soil and climatic conditions and on historical and social factors, in some places there is a mixture of these two oaks, while in others they are found with other species including Quercus faginea (Portuguese Oak), Quercus canariensis (Algerian Oak), Olea europaea ssp. sylvestris (Wild Olive) and Pinus pinea (Stone Pine) (Fernández Martínez, in press). Trees of the genus Quercus are widespread in the northern hemisphere and are a significant species in many forests and woodlands (Cañellas et al., 2006; 2007). In the Mediterranean Basin and Middle East, the Holm Oak, a sclerophyllous evergreen tree, is found over an area of roughly 6,000 km east-west, from Syria to Portugal, and 1,500 km north-south, from France to Morocco and Algeria (Debazac, 1983). On the Iberian Peninsula, Holm Oak is a very abundant species, occupying a wide range of ecological niches, and occurring in humid, subhumid, and semiarid regions (Afzal-Rafii et al., 1992). Overall, on the peninsula, it covers a total area of about 2.5 million ha (García-Mozo et al., 2007), representing 54% of the total area occupied by hardwood species (Ministerio de Medio Ambiente, 1997). Dehesas have been, and still are, very important for the economy of the areas where they are found. Regular income is mainly obtained from livestock, but also from hunting, fuelwood, coal and non-timber products such as cork, fungi, fodder, various types of fruit and honey. Livestock farming is linked to high-value native breeds (Ezquerra, 2009). In addition to their use for livestock, dehesas also have an important role as an ecological niche for a great diversity of species of flora and fauna, many of them well adapted, even dependent on the human presence and its livestock (Fernández et al., 2008b). Overall, dehesas are of great economic, ecological, social and aesthetic value to the Iberian Peninsula (Diaz et al., 2007). Further, tree-populated dehesas are listed among the habitat types protected under the European Union’s Habitats Directive (Alejano et al., 2008). Unfortunately, nowadays, dehesas are threatened by poor regeneration, inappropriate livestock management and the, in some places dramatic, effect of the disease “oak decline” (Díaz et al., 1997). This disease is produced by the interaction of several factors including the fungus Phytophthora cinnamomi, several insects, the ageing of trees and/or climate change (Diaz et al., 1997), and mainly affects the southwestern part of the Iberian Peninsula, where dehesas are currently severely vulnerable. In this context, it is even more important to know more about the ecological functioning of these forests and the influence of management practices on their ecological balance. The complexity of the management of dehesas, partly due to the threats they are under, makes it necessary to reconsider, and sometimes change, traditional management practices applied to these agroforestry systems. Very simplistic proposals, attempting to manage only certain parts of the elements of the system, should be avoided. Dehesas cannot be managed just like an agricultural system, a livestock system, or a forestry system, but rather require the implementation of comprehensive management models considering production and conservation.

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Dehesas: Open Woodland Forests of Quercus in Southwestern Spain

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2. ECOLOGY AND PRODUCTIVE PROCESSES 2.1. Climate and Soils In the southwest of Spain, open woodlands grow under a Mediterranean climate. This climate is characterized by the periods of the highest temperatures and the lowest precipitation occurring at the same time in the year, leading to a summer drought that typically lasts for longer than three months1. Precipitation is highly variable but the annual mean is more than 250-300 mm, while the mean annual temperature is lower than 21ºC, with the mean temperature being higher than 6ºC in all months and the mean temperature of the warmest month being higher than 22ºC. These general conditions exist between the latitudes of 30º and 40º in both hemispheres in the western parts of the continents, including areas in California (USA), central Chile, South Africa, Australia and the Mediterranean basin. It is recognized as a separate climate in most world climate classifications, being classified as Csa, IV and B1 in the Köppen, Walter and Austin-Miller classifications respectively. In open forests of southwestern Spain there are several different local types of Mediterranean climate according to proximity to the Atlantic Ocean or Mediterranean Sea, altitude and influence of the Sierra Morena and Penibetic mountain ranges. Here we illustrate the general climatic characteristics of the area and local differences with climatic data from seven weather stations. The main climatic variables and climodiagrams of these locations are presented in Table 1 and Figure 1 respectively and their geographical location in Figure 2.

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Coastal areas (reference: Huelva and Tarifa stations). The coastal areas receive from 500 mm up to 800 mm of precipitation, mainly in winter months, increasing as you move from Huelva to the Strait of Gibraltar. The thermal variation is the lowest in the region with mean temperatures in January of around 11-13ºC and in July of around 23-26ºC, the mean annual temperature being 18ºC. Frosts are very rare, with mean of minimum temperatures in January as high as 6ºC on the coast of Huelva and 10ºC in the proximity of the Strait of Gibraltar. The drought season lasts for around 5 months. Guadalquivir valley (reference: Ecija station). As we move east from the coastal region into the Guadalquivir valley there is more thermal variation, with the mean maximum temperatures in July being as high as 38ºC, 5.5ºC more than in the coastal region of Huelva and 11ºC more than in the coastal areas near the Strait of Gibraltar. The mean annual precipitation is 550-600 mm, slightly higher than in the coastal region of Huelva, and is more evenly distributed between winter, spring and autumn. Sierra Morena mountain range (reference: Aracena and Pueblo Nuevo stations). The mountain range of Sierra Morena acts as a mountain barrier to the wet southwesterly winds that are common in winter months. Hence, precipitation increases on the southern slopes up to 1100 mm with a winter peak. As we move east, the precipitation decreases (values of 900 mm in Pueblo Nuevo) and the climate

1

We will follow Gaussen’s definition of meteorological drought (Gaussen, 1953), considering drought to be when the precipitation in mm is lower than twice the mean temperature of the month in ºC.

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R. Alejano, J. Vázquez-Piqué, J. Domingo-Santos et al. becomes more continental with mean minimum temperatures in January of 1.5ºC and frosts are more frequent. The drought period is reduced to around 3.5 months. Guadiana Basin (reference: Almendralejo station). On the northern slopes of the Sierra Morena mountain range, precipitation decreases rapidly as we move towards the Guadiana river. In the proximity of Guadiana river the mean rainfall is less than 450 mm and the drought is the most intense (5.2 months) in the region. Penibetic mountain range (reference: Ubrique station). The Penibetic range also acts as a barrier to humid southwesterly winter winds. Hence, precipitation is very high in winter months, reaching annual values as high as 2200 mm in the mountains around Grazalema, and the dry period lasts slightly longer than 3 months. In summer, it is common for there to be easterly winds due to low pressure areas over the north of Africa that lead, due to the orientation of these mountains, to Föhn winds at the western and northern regions of the range. This situation results in the highest temperatures of the year and heat waves with temperatures rising to above 45ºC in the central Guadalquivir valley.

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Table 1. Main climatic characteristics of seven weather stations of southwestern Spain. Alt: Altitude (m); P: Annual precipitation (mm); T: Mean annual temperature (ºC); Tc: Mean temperature of the coldest month (ºC); Tw: Mean temperature of the warmest month (ºC); Tmc: Mean minimum temperature of the coldest month (ºC); TMw; Mean maximum temperature of the warmest month (ºC); a: number of dry months (months) Location

Latitude Longitude Alt

P

T

Tc

Tw

Tmc TMw a

Huelva

37º16`

6º54`

19

512

18.1 11.0 25.7 5.9

32.5

4.7

Tarifa

36º01`

5º36`

20

794

18.0 13.4 23.5 10.5 26.9

4.4

Écija

37º32`

5º05`

112 539

18.9 10.4 28.5 4.4

37.9

4.9

Aracena

37º54`

6º34`

731 1016 14.6 7.0

24.7 3.1

33.3

3.2

Pueblo Nuevo

38º05`

4º55`

410 898

16.3 8.0

26.1 1.5

35.2

4.0

Almendralejo

38º41`

6º24`

336 419

16.9 8.3

26.7 3.9

34.7

5.2

Ubrique

36º41`

5º26`

337 1213 16.6 10.4 24.2 4.3

32.6

3.3

Soil is the main environmental feature that defines the areas of dehesas at a regional scale. These agroforestry systems have been preserved because the land was mostly unsuitable for intensive farming, due to the stony, shallow, and nutrient-poor soils. The dehesa woodlands appear mainly on siliceous sedimentary materials formed between the Precambrian and the Carboniferous periods. Intense folding and volcanic events occurred during the Hercynian or Variscan orogeny creating high mountains; now, after 250 My, they have mostly eroded down to the present landscape, alternating rolling hills with gentle valleys. Under the soil of dehesas, it is common to find sedimentary rocks such as shale, sandstone (wacke) and siltstone; metamorphic rocks, such as phyllite; and igneous rocks, such as granite, rhyolite and dacite. These rocks have, in general terms, low base content and the constituent minerals have a low weathering rate, leading to shallow to intermediate soil profiles (less than one meter deep), rich in coarse fragments. The Mediterranean climate tends to mean that there are relatively few days per year with suitable conditions, moisture available in the soil and warm enough temperatures, to enhance rock weathering. There is, however,

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enough annual rainfall to cause clay illuviation in deep horizons, either from a downwards movement of clay or from clay production after rock weathering in deep horizons that stay humid during the spring and a part of the summer.

Figure 1. Climodiagrams of seven weather stations in southwestern Spain. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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Figure 2. Location of the weather stations of Huelva, Tarifa, Écija, Aracena, Pueblo Nuevo, Almendralejo and Ubrique and main mountain ranges and valleys in southwestern Spain.

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Thus, the most common diagnostic horizon is the argic horizon, a subsurface horizon with distinct higher clay content than the overlying horizon (IUSS Working Group WRB, 2006). A soil survey of over 100 dehesa soil profiles in SW-Spain (Domingo-Santos et al., 2011; 2010a; 2010b; 2006) revealed that 75 profiles had an argic horizon; Luvisols is the most common group, followed by other groups with low base content, such as Alisols, Acrisols and Lixisols (Figure 3 and Figure 4).

Figure 3. Soil transect in a dehesa. The slow weathering quartz-rich igneous rock results in stony, shallow profiles at the top of the slope. The gently curved slope allows water to accumulate downhill, leading to a greater depth and horizon development. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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Soil depth (cm)

120

50 45 40 35 30 25 20 15 10 5 0

100 80 60 40 20 0

Regosol

Phaeozem

Luvisol

Lixisol

Leptosol

Cambisol

Alisol

Acrisol

Average soil depth

Number of profiles

MAIN FAO GROUPS IN DEHESAS

Number of profiles

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Figure 4. Average soil depth (in cm) of the taxonomic groups of the FAO WRB (IUSS Working Group WRB, 2006) and number of profiles of each group found in a survey of 100 soil profiles under dehesa woodlands, in SW-Spain (Domingo-Santos, 2002; Domingo-Santos et al., 2011).

As for soil profiles that do not have an argic horizon, there are Cambisols and Regosols groups and these are commonly found either at the top of slopes or in other highly eroded areas, or in deposition areas. Rock type has an important influence on soil formation in this Mediterranean environment. Figure 5 and Figure 6 are flowcharts describing the most common soil WRB reference soil groups in dehesas over volcanic acid rocks and shale-type rocks respectively. Though both types have stony and poor soils, the shale rocks allow greater soil evolution and this leads to Haplic (typic) Luvisol being the most common group. Water holding capacity is low to moderate in acid volcanic rock soils, whereas in shaletype rock ranges from moderate to very high. Leptic Regosol (Skeletic)

Leptic Cambisol (Skeletic)

Leptic Luvisol (Skeletic)

Leptic Acrisol (Skeletic)

Figure 5. Soil groups occurring in dehesas over ancient (Paleozoic) volcanic acid rocks (DomingoSantos et al., 2006; 2010a).

Regarding organic matter, the average carbon content found in the dehesa soil survey was 37.4 t·ha-1; the value varies significantly with rock type ranging from average values of 26.6 t ha-1 on volcanic acid rocks and 33.9 t·ha-1on shale-type rocks, to 60.0 t ha-1 on deep sandy quaternary soils (Domingo-Santos et al., 2010 c). In conclusion, under a Mediterranean climate, soil conservation becomes a mayor issue for dehesa agroforestry systems; whereas grass may dry out completely, trees need some soil moisture to survive the drought and extreme heat of the summer (see Figure 7), meaning that soil losses really threaten the survival of dehesas. The abundance of rock fragments in these

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soils may be considered as a protecting factor (stone mulching), but the most efficient protection against erosion is to maintain a complete and not overgrazed grass cover and, as far as possible, avoid ploughing. Leptic Regosol (Dystric, Skeletic)

Haplic Luvisol (Dystric)

Haplic Alisol Leptic Acrisol (Skeletic, Chromic)

Leptic Cambisol (Dystric)

Haplic Lixisol

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Figure 6. Soil groups occurring in dehesas over ancient (Paleozoic) shale rocks (Domingo-Santos et al., 2010b).

Figure 7. Distribution of available water holding capacity for the dehesas soils. Most soils range from low to high, where very low is under 35 mm, low is under 70 mm, medium under 105 mm, high under 140 mm and very high is greater than 140 mm.

2.2. Physiological Traits The most important factor limiting the establishment, subsequent growth and plant distribution in Mediterranean ecosystems is summer drought. Drought induces vegetation water stress, so trees must develop strategies to maintain their water status during periods of severe water deficit. These include changes in gas exchange, leaf area, rooting depth, stomatal opening, and osmotic adjustment, among others. For this reason, the water status of plants needs to be considered when assessing plant phytosanitary status (Larcher, 2003). Moreover, it is important not only to make this assessment in summer, but rather to investigate the seasonal evolution of physiological water relations and their response to water stress, since there is no common oak strategy for water regulation during dry periods (Abrams, 1990). Accordingly, the seasonal evolution of the xylem water potential (Ψ) and other water relations parameters, namely, gas exchange and specific leaf area (SLA), were determined for six years on young shoots (≤ 1 year old) of Holm Oak trees on three field plots, from an open woodland ecosystem in southwestern Spain.

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Xylem water potential at dawn (Ψ) ranged from -0.5 ± 0.2 MPa to -3.7 ± 0.5 MPa (mean ± SE) depending on the field plot, the year and the date, ranging from -2.5 to -4.1 MPa during summer. Typical values indicating onset of severe water stress for Holm Oak are between 3.0 and -3.5 MPa (Aussenac and Velette, 1982; David et al., 2002; Pesoli et al., 2003). Our data showed average Ψ values below -4.1 MPa during the summer months of 2004 and 2005, as a consequence of the severe drought in the area in those years. Water stress usually decreases transpiration and photosynthesis rates in Holm Oak and the carbon fixed by photosynthesis may fall by as much as 40% when soil moisture decreases by 15% (Ogaya and Peñuelas, 2003). In our study, during the summer, when Ψ did not fall below -3.5 MPa, gas exchange rates decreased to 20–40% of the spring values; net photosynthesis rates, however, were positive during the morning hours. By contrast, when Ψ was severely affected by the drought (≤-4.0 MPa) photosynthesis rates fell from 15% of the highest spring levels to negative values. This means a reduction in growth rate and storage of energetic reserves; the latter playing a key role in osmotic adjustment in this species (Serrano and Peñuelas, 2005; Fernández et al., 2008a). Parameters related to cuticular transpiration (Ec) indicated a clear strategy for preserving water during drought periods, namely, the changing of morpho-physiological traits. This was evident in our study through the stomatal closure and the decrease in Ec during the driest periods (~70 µmolH2O kg-2 s-1), as well as the highest values (~90%) of relative water content at the point of stomatal closure (RWCc). During periods of greater water availability, this species tended not to control water loss to the same degree (Ec = 150-175 µmolH2O kg-2 s-1; RWCc = 60-80%), and hence is described as a ‘‘water-spender’’, preserving water during dry periods but not during wet ones (Pena-Rojas et al., 2005). There were small but significant differences in SLA between seasons during the study. Specifically, monthly average values ranged from 2.82 ± 0.08 m2 kg-1 in summer to 4.14 ± 0.10 m2 kg-1 in winter. In addition, SLA and Ec (n= 320; r= 0.595; p -2.7 MPa; PLC < 55%), the recovery of and PLC were satisfactory after a rain event, and they were not a major limitation for AP; but under more severe water stress ( at dawn < -3.0 MPa; PLC > 68%) the loss of hydraulic conductivity, together with the stomatal closure and the loss of cell turgor, seriously limited AP. Under the climate change scenario of drier conditions in the Mediterranean basin, the negative effects of summer drought on Holm Oak water status, tree growth and fruit production would become more severe, which in turn would have a negative impact on ecosystem dynamics. Therefore, forest management practices affecting vegetation and soil should be focused on increasing soil water holding capacity and decreasing soil water consumption, to thereby avoiding at dawn falling below -3.0 MPa and the PLC of twigs below 68%. In addition, as there were differences in the seasonal evolution of plant water status, water conservation, frost and drought tolerance as a function of provenance (Andivia et al., 2011a, b), we suggest that reforestation programmes should consider to a greater extent provenance of Holm Oaks in question and their tolerance of various abiotic stressors.

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2.3. Main Productive Processes 2.3.1. Acorn Production Acorn production is a key factor in the ecology and economy of dehesas. From the point of view of economics, acorns are used for feeding livestock and specifically Iberian pigs, with which the quality of the product (meat) and its market value depend on acorn consumption (Alejano et al., 2011). When the period of acorn fall starts in dehesas, the pigs weigh 90-120 kg, and after three months they reach 160-180 kg, acorns and fresh grass being the main components of their diet during this time (Consejería de Medio Ambiente, 2004). From an ecological point of view, acorn production plays a fundamental role in the organization and dynamics of forest ecosystems, and both annual and individual variations in yield influence the management and regeneration of oak forests (Healy et al., 1999). As Koenig et al. (1994) comment, the size and variability of acorn crops are not only essential to the life history of oaks, but are also important to the diverse assemblage of birds and mammals that rely on acorns as a major food resource. Acorns are the most nutritionally valuable food resource for a number of mammals, birds and insects, including game and non-game wild species (Greenberg, 2000), and play a fundamental role in the dynamics of pests and diseases within these systems (Carbonero, 2011). Acorns should also guarantee the natural sexual regeneration of trees. The lack of regeneration is, however, one of the main problems in dehesas, as natural processes are restricted by the presence of livestock and its management, among other factors.

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Acorn development in Quercus ilex is very slow during spring and summer, and the fruit is still very small (less than 0.5 cm in diameter) in early September the point at which a fast growth period starts (Siscart et al., 1999). Spring and summer are, nevertheless, very important for acorn production, because climatic parameters in this period seriously influence flowering. In dehesas, the dissemination period when acorns fall to the ground and are eaten by livestock, is known as the “montanera”. For Quercus ilex, this period usually starts in September-October, ending in January. The forecast and measurement of acorn production would improve management of the montanera period, and are very important to evaluate the potential impact on the dynamics of wild fauna populations and Quercus regeneration. Nevertheless, acorn production is not an easy process to assess because of the great variability of the yield between years, sites and individual trees (Martin et al., 1998; Cañellas et al., 2007; Carbonero, 2011). Average acorn production of several areas of dehesa (50 trees) in the province of Huelva is shown in Figure 10 for a nine-year period (2001-2009): differences can be observed between years, but no clear cyclical pattern. There is also a general decrease in yield over the years; notably, the peaks reached in 2002 and 2003 have not been reached again (up to 2009), which is worrying. Figure 11 shows average yield per tree and year in a plot in San Bartolomé (province of Huelva), illustrating differences between years and the same tendency of decreasing yields. Average acorn production for Quercus ilex and Quercus suber for western and southwestern Spain according to various authors is shown in Table 2.

Figure 10. Average acorn production (grams of fresh matter per m2 of crown area ± standard deviation) per tree per year, measured in three plots in the province of Huelva.

The yield of individual trees is highly variable between and within years, depending on several environmental and endogenous factors (Carevic et al., 2010) (Figure 12). Plant water status during summer is likely to be a major factor affecting seed growth and acorn production. Alejano et al. (2008) found a positive relationship between water potential (measured in midsummer) and acorn production indicating that trees require a certain level of water availability for acorn development during the summer and the beginning of the autumn.

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Resource scarcity, such as low water availability, is a main reason for the premature abortion of fruit (Larcher, 2003) and typically occurs at the beginning of seed development.

Figure 11. Peak acorn production (grams of fresh matter per m2 of crown area ± standard deviation) per tree per year, measured in the San Bartolomé plot.

Table 2. Acorn production for dehesas in western Spain (R/P: Region/Province; SP: species; AP: acorn production; QI: Quercus ilex; QS: Quercus suber; DM: dry matter; FM: fresh matter) Authors, year Martín et al., 1998

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Álvarez et al., 2002 Carbonero et al., 2002 Poblaciones et al., 2006 García Mozo et al., 2007 Cañellas et al., 2007 Alejano et al., 2008

R/P Western Andalusia Salamanca

SP QI

Córdoba

QI

Extremadura

QI

AP (g/m2) 11.6-285.8 DM

AP (kg/tree) 1.3-42.1 DM

AP(kg/ha) 550 FM 475 FM

363 FM(max 1383)

19 FM (0.1287.85) 18 FM (9.79-130)

QI

QI Extremadura

QS

Huelva

QI

600-830 DM 8-14 FM (range 0.5150) 0.7-332.8 FM 95.1 DM (max 1016.4)

6.5 DM

590-830 FM 227 DM

For a better understanding of the factors affecting acorn production, it should be noted that total acorn production (in weight) is the product of two components: number of acorns and the average acorn mass. The number of acorns is related to the processes of flowering and flower survival while acorn mass is related to the accumulation of reserves in the fruit. The trade-off between offspring weight and number has been a foundation of much of the theoretical work on life history patterns (Smith and Fretwell, 1974; Wilbur, 1977). Many authors have observed an inverse relationship between offspring size and number in a wide range of plant species (Abrahamson and Layne, 2003), and these patterns have also been found in Quercus ilex in southwestern Spain (Alejano et al., 2011).

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Figure 12. Average acorn production (g/m2 of crown area ± standard deviation) per tree in the Huerto Ramirez plot (Huelva) for the period 2006- 2009. Numbers on the x- axis are identifiers for individual trees.

Estimated average acorn mass for SW Spain is within the range 1.2-6.5 g (Gea-Izquierdo et al., 2006; Alejano et al., 2011). Variations between years have been reported and can be explained by climate. In particular, climatic conditions at the end of the summer drought (September), the fattening period for acorns (Siscart et al., 1999) when water stress is greatest, are very important. Parameters associated with more intense drought in September (high temperature, evapotranspiration and radiation; and low precipitation) are associated with lighter acorns. When the summer drought was less intense, a higher maximum temperature in June and greater radiation in July were associated with heavier acorns (Alejano et al., 2011). Tree pruning and other silvicultural practices that have changed little over the past few decades have traditionally been used in dehesas (Navarro et al., 2002). In particular, the objective of maintenance pruning is to maximize acorn yield, and it is often believed that pruning has a favourable effect on acorn production (Cañellas et al., 2007). On the other hand, researchers working on this topic have not found significant differences in acorn production as a function of pruning type or intensity, comparing production with non-pruned trees (Cañellas et al., 2006; Gea- Izquierdo et al., 2006; Alejano et al., 2008). Given these results, the decision to prune Holm Oaks in the dehesa should be made according to other criteria, such as tree health, economic factors, or the need for fuelwood.

2.3.2. Diameter Growth The growth of forest trees has traditionally been studied for its role as a source of wood and forestry has focussed on timber productivity since it became a scientific discipline in the 17th century (Bravo et al., 2011). Nevertheless, growth is also a good indicator of tree health, the influence of ecological features, competition and endogenous functioning of each tree, making it possible to analyse the effect of forest disturbance, both natural (floods, pests, etc.) and anthropogenic (pollution, fires, etc.). Moreover, analysis of diameter growth may be highly useful to assess the response of Holm Oak (Quercus ilex) to a likely global climate

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change scenario of increasing temperatures and lower precipitation (IPCC, 2007). In particular, it may enable us to forecast its future distribution. Holm Oak is a very slow growing species, but well suited to the Mediterranean climate. Indeed, a characteristic that distinguishes the evergreen Holm Oak from deciduous oak species is that it can successfully cope with dry conditions. The most xeric subspecies, Quercus ilex ssp ballota, is capable of growing under the extremely dry conditions of the Mediterranean summer, even 50% of hydraulic conductivity remaining at a xylem pressure potential of -5.6 MPa (Corcuera et al., 2004). Despite its importance, to date there have been few studies investigating Holm Oak growth behaviour, and most of those carried out have been based on dendrochronological methods (i.e., analysing tree-ring width or other anatomical features of wood), regardless of the existence of false or missing rings and the difficulty of determining growth ring boundaries in this species (e.g., Zhang and Romane, 1991; Cherubini et al., 2003; GeaIzquierdo et al., 2009; Nijland et al., 2011). While such techniques are very helpful to determine long-term growth, previous climatic conditions and historic disturbances, retrospectively they are not suitable to accurately determine the intra-annual pattern of Holm Oak growth and its relationship with current climatic conditions in each period. Intra-annual growth studies can reliably help determine the onset of growth cycles, their duration and magnitude, and which ecological factors govern them. This knowledge is very useful to accurately assess how forests develop under current and future climatic conditions, their role as sinks for CO2 and how forestry management can help to mitigate the impact of climate change on forests. Therefore, it is necessary to accurately determine the seasonal changes in this slow-growing species within and between years and to assess the influence of climatic factors. The Holm Oak stem growth shows a marked seasonality (Figure 13), with significant differences between months and growth concentrated in spring and autumn, the seasons that are most favourable for plant growth in the Mediterranean climate (Mitrakos, 1980). Growth spurts may also occur in late winter or even early winter when mild temperatures allow it, active growth continuing through spring until early summer when water stress induces stomatal closure, causing dormancy to reduce the risk of embolism. In addition, in the summer the Holm Oak develops its acorns and there is trade-off between acorn production and stem growth (Martin et al., 2010b), acorns storing nutrients and energy that could otherwise be used for growth. After the summer drought, the stems are rehydrated with September rains, and this coincides with a rise in photosynthetic activity (Corcuera et al., 2005); it is assumed that at this point the growth resumes (until winter), when low temperatures induce cessation of cambial activity or growth slows. This bimodal behaviour of growth is also often responsible for the intra-annual fluctuations observed in the density of this species (Cherubini et al., 2003), which is consistent with the presumed sub-tropical origin of many evergreen species of the Mediterranean flora, such as the Holm Oak (Palmarev, 1989; Gutierrez, 2011). Nevertheless, this exact pattern it is not seen in all years (Figure 14) due to the Mediterranean climate variability, e.g., rather dry winters and spring or cold autumns can drastically reduce growth.

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0.05

Mean daily growth (mm day-1 )

0.04

0.03

0.02

0.01

0.00

-0.01

-0.02 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Figure 13. Estimated values of daily growth rate of the stem circumference (mm day-1 ± standard deviation) per month in Holm Oak throughout the 2004-2006 period in Huelva (Andalusia, SW Spain). Data obtained with band dendrometers.

Mean daily growth (mm day-1 )

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0.08

0.06

0.04

0.02

0.00

-0.02

-0.04 Jan

Feb

Mar

Apr

May

2004

Jun

Jul

2005

Aug

Sep

Oct

Nov

Dec

2006

Figure 14. Estimated values of daily growth rate of the stem circumference (mm day-1 ± standard deviation) per month and year for the 2004-2006 period in Huelva (Andalusia, SW Spain).

On the other hand, there are significant differences in growth between locations (Figure 15), suggesting a remarkable influence of particular ecological and/or management characteristics of the site. Furthermore, in Holm Oak, there are significant differences between individuals that are not explained by plot location but seem to be partially attributable to tree size.

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Mean daily growth (mm day-1 )

0.05

0.04

0.03

0.02

0.01

0.00

-0.01 2004

2005

2006

2007

HR

2008

HI

2009

2010

SB

Figure 15. Estimated values of daily growth rate of the stem circumference (mm day-1 ± standard deviation) per year and location in three different locations in Huelva (Andalusia, SW Spain).

Monthly temperature and precipitation have a significant effect on growth. As shown in Figure 16, precipitation is the major climatic factor in Holm Oak growth. In late winter and spring, the increased availability of water enhances growth and the annual peak is reached. On the other hand, the high summer temperatures drive water loss by increasing evapotranspiration and growth slows down, and it can even be negative between two measurement dates due to drying of the stem. 0.2000

1200 P(mm)

0.1500

1000

Mean daily growth (mm day-1)

900

0.1000

800 700

0.0500

600 500

0.0000

T(ºC)

400 300

-0.0500

200 100

-0.1000

PRECIPITATION

MEAN DAILY GROWTH

Dec-06

Oct-06

Nov-06

Sep-06

Jul-06

Aug-06

Jun-06

Apr-06

May-06

Mar-06

Jan-06

Feb-06

Dec-05

Oct-05

Nov-05

Sep-05

Jul-05

Aug-05

Jun-05

Apr-05

May-05

Mar-05

Jan-05

Feb-05

Dec-04

Oct-04

Nov-04

Sep-04

Jul-04

Aug-04

Jun-04

Apr-04

May-04

Mar-04

Jan-04

0 Feb-04

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1100

MEAN TEMPERATURE

Figure 16. Influence of precipitation and mean temperature on mean daily growth rate of stem circumference (mm day-1 ± standard deviation) per month and year for 2004-2006 period in Huelva (Andalusia, SW Spain).

However, as shown in Figure 16 and reported by Corcuera et al. (2004) and Gutierrez et al. (2011), summer rainfall can rapidly reactivate the growth. Conversely, low temperatures and the short photoperiod in winter reduce the positive effect of late autumn and winter precipitation.

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2.3.3. Phenology and Litterfall Phenology is associated with periodic biological events related to plant life, such as flushing, flowering and fruit development and maturation (Font Quer 1989). These events are strongly correlated with climatic conditions and are important to understanding the reproductive patterns of the species, as well as the potential for natural regeneration (FAO, 1993) and adaptation to different climate change scenarios. Quercus ilex and Quercus suber, the main species in the Spanish dehesas, are monoecious species with unisexual inflorescence. Normally, most flower buds and flowers appear from March-April to May-June on branches with new growth. In these species, there are large differences in flowering time and phenology between trees and years, which facilitate gene mixing within populations. Acorns mostly mature and fall in NovemberJanuary but Q. suber can have an annual and biennial ripening cycle. The biennial cycle is more common in the northern populations, whilst the annual cycle is more often seen in the southern cork oak woods (Díaz & Fernández, 2000). The summer dry season of the Mediterranean climate often restricts vegetative growth to a period between spring and early summer. In this period, the soil usually has sufficient available water and the temperature is above the threshold for the development of new shoots and leaves. Even in the warmest areas in the southwest of Spain, with mean temperature and mean minimum temperature in January as high as 12ºC and 6ºC respectively, we have not detected vegetative growth or cambial activity in stem and branches, indicating that temperature is a limiting factor for vegetative growth even in this area. Under these circumstances, it would be expected that plants would develop their leaf biomass as fast as possible at the beginning of the growth season, in order to take advantage of this period of more favourable temperatures and rainfall for photosynthesis and metabolic activities (Mediavilla & Escudero, 2009), as well as translocating water and nutrient resources from senescence leaves to the new ones. Holm Oak (Q. ilex) and Cork oak (Q. suber) do indeed concentrate leaf emergence in a single flush at the beginning of the growth season, from the end of February in the south of Spain until May in the north. In addition, a second flush may occur at the end of spring if water is still available in the soil at that time. This renewal of foliage is the main source of litterfall in Mediterranean Quercus species. Forest litterfall has a key role in the transfer of energy and nutrients to the soil (Andivia et al., 2010), providing the main aboveground contribution of carbon and nutrients to the forest floor (Gallardo et al., 1998). In addition, litterfall also has a direct and indirect influence on soil physical and chemical properties, buffering changes in soil water content and temperature, hindering erosion, and increasing nutrient availability and the diversity of plant, fungi and animal species in the soil (Sayer, 2006). Although litterfall might be influenced on a regional scale by other factors, such as topography, difference in soil water content or nutrient availability (Blanco et al., 2008), litterfall is mainly governed by climate and seasonality, showing a strongly seasonal pattern with a large peak in spring (March-June) and another much smaller one in autumn (October-November) (Figure17). The two species are considered evergreen species, although they have different foliage renewal strategies. Q.ilex renews part of its leaf cover in spring, simultaneously with the growth of new shoots. Its leaf lifespan ranges from less than one up to four years, usually being around 2 years since most leaves are shed at the start of their third year. Leaf turnover rates vary greatly with crown position, habitat characteristics and weather (Rodá, 1999). On the other hand, Q. suber renews all its leaf cover in spring, with a gradual substitution of

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leaves as the new shoots are developing; in fact, Q.suber produces more litterfall than Q.ilex (Figure17). By May or June, the tree has whole new set of leaves and its leaf lifespan is around 12 months. In years with a dry winter and spring, both species can stop leaf renovation, and maintain the old leaves until there is sufficient water available in the soil, waiting until the autumn rains. In this case, both species can exceptionally flush in autumn and, in some trees, produce male flowers. The interannual variability in litterfall, mainly influenced by variability in leaf fall (around 60% of total litterfall) (Figure18), is related to Mediterranean climate variations, in particular the variability in rainfall. 90 Q. suber

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Figure 17. Litterfall seasonality (gm-2 dry mass ± standard error) of a Quercus ilex and Quercus suber dehesas in Huelva (SW Spain), over a period of six years of monthly litterfall collection (2004-2009).

The strong relationship between climate, phenology and litterfall suggests a potential effect of climate warming on litterfall production and seasonality. Recent studies have indicated an absence of new leaves and, therefore, longer leaf retention and leaf span in Holm Oaks subjected to spring droughts (Misson et al., 2011). Such changes may affect the amount of nutrients returned to the forest floor that in the long term could affect nutrient cycling and site productivity. The importance of litterfall in the functioning of forest ecosystems, and its strong relationship with phenology and climatic conditions, make it important to increase our understanding of these relationships as a fundamental aspect of good forest management. This is especially important for Mediterranean dehesas where water and nutrients are limiting factors and models of climate change in these areas predict increasing temperatures and more severe droughts. Management practices can also influence litter production and seasonality, pruning being the main management practice that could change litter production in Mediterranean dehesas. Specifically, pruning reduces aboveground biomass and, consequently, future litterfall production, and, moreover there is no significant increase in nutrient return to the soil from pruned material as it is usually used for firewood rather than being left on the forest floor. Our experience is that litter production is influenced by pruning during the first season after it is conducted, pruned trees sprouting earlier and producing less litter. The effort of sprouting

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during this first year involves a reallocation of resources to rebuild the aboveground biomass and might influence acorn production and tree growth. 350 Litterfall Leaves Fall 300

(g·m-2)

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Figure 18. Litterfall and leaves fall (gm-2 dry mass ± standard error) over a period of six years (20042009) in a Quercus ilex forest in Huelva (SW Spain).

3. DEHESA MANAGEMENT

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3.1. Silvicultural Treatments and Main Types of Production Now, at the beginning of the 21st century, the sustainability of dehesa landscapes faces a major challenge. On the one hand, they need to retain their cultural role and provide products and services demanded by society. On the other hand, preservation of the proper functioning of the system requires traditional management (Pérez- Soba et al., 2007). Given this, the management of dehesas does not attempt to maximize the output of any particular product; on the contrary, it focuses on efficiency and diversification. Management practices in dehesas mainly prioritise: Pasture production. Non-timber production, such as that of acorns and cork, as well as firewood and game. Services or indirect benefits, i.e., improved environment, biodiversity, high-quality landscape, carbon sequestration, etc. With respect to pasture production, management practices aim to correct inappropriate grazing intensities. Overgrazing usually leads to pasture degradation due to the substitution of grass species valuable as forage by others which are inedible or of lower nutritional quality. On the other hand, areas less intensively grazed tend to be colonized by bushes. Shrub control is important for pasture production but also for fire prevention, and, to a lesser extent, for controlling competition with trees (Serrada and San Miguel, 2008). Soil tillage (with or without sowing) and brush clearing are the main strategies for pasture maintenance.

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Regarding trees and their interactions with the rangeland system, management practices tend to focus on optimizing acorn production, as well as tree conservation and regeneration. The main practices used are tree pruning and regeneration activities.

Tillage Tillage in dehesas is a low-cost practice that aims to eliminate woody vegetation and to promote grass regeneration and growth. On the other hand, it has other undesirable effects and should be avoided in most cases. In particular, tillage leaves soil unprotected against raindrop impact; lack of vegetation and loose soil greatly increase erosion. Moreover, tillage destroys natural tree seedlings and may contribute to spreading tree fungi such as Phytophthora sp., while it does not improve tree growth. Experimental studies conducted in dehesas have found no significant influence of soil treatments on annual stem circumference growth (Martin et al., 2010) (Figure 19). 18

Annual growth (mm)

16 14 12 10 8 6 4 2 0 2006

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Control

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Figure 19. Effects of soil treatments on annual growth ± SD of stem circumference in Quercus ilex dehesas (southwestern Spain).

Thus, tillage practices should be limited to certain special contexts, such as maintenance of fire breaks and pasture restoration, the latter along with grass sowing.

Brush Clearing Brush clearing, using brush cutters and mulchers, is an alternative to tillage for controlling shrubs. Root systems and surface organic matter protecting the soil stay unaltered, so this practice does not affect erosion or tree health. Brush clearing is, however, more expensive than tilling and it should be applied in a selective way. It must be taken into account that shrubs may have a positive effect on seedling protection and soil cover, as well as increasing biodiversity and providing fodder. Accordingly, certain guidelines should be followed in this type of clearing: apply selective clearing, keeping species that have value as forage or protect seedlings; create a patchwork landscape by leaving uncleared areas; and consider sowing grass when the treatment is likely to lead to soil disturbance (Alejano, in press).

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Pruning Traditionally, dehesa trees have been subjected to two types of pruning. Firstly, formative pruning, which is carried out only once during a tree’s lifetime (typically at an age of 30–40 years, when trees are ca. 15 cm in diameter at breast height), and aims to create a single trunk about 2.5 m in height and a crown composed of three or four evenly spaced main branches. Secondly, maintenance pruning is done every 6–10 years and involves reducing crown volume by removing branches in the central and other inner parts of the tree crown; this restricts water supply to leaves with respect to that available in a naturally growing crown and causes leaf growth to be encouraged further from the trunk. Maintenance pruning is intended to maximize acorn yield, and forest owners tend to believe that pruning has a favourable effect on acorn production (Cañellas et al., 2007). It is, however, unclear whether it actually increases acorn yield as traditionally thought (San Miguel, 1994) as the outcome is influenced by pruning intensity. The financial costs of light or moderate pruning are very high in any case, and attempts to offset such costs by obtaining income from firewood, charcoal or virgin cork have led producers to increase pruning intensity. As a result, pruning is sometimes very intensive and in some cases excessive (Cañellas et al., 2002). Although the influence of pruning on acorn production in Mediterranean oak woodlands has long been controversial, it has not been well documented until recent times. Cañellas et al. (2007) found that moderate pruning (removing 30% of crown biomass) in a mixed Q. ilex-Q. suber dehesa had no effect when acorn production was poor, but it seemed to decrease production when it was good. Alejano et al. (2008) investigated the effects of pruning on Q. ilex in more detail, comparing oaks that had been subjected to light, moderate and heavy traditional pruning along with a non-traditional method of ‘crown-regeneration pruning’ in which the outermost branches of the tree crown were removed, thereby shortening water transport distances and resulting in a more compact crown that was hypothesized to improve water balance. Results from over five years failed to indicate any significant overall effect of traditional pruning on either absolute or relative acorn production. There was, however, evidence that the non-traditional approach significantly enhanced acorn production, indicating that while it is questionable whether traditional methods of pruning have beneficial effects, new methods taking into consideration the architecture of the trees may increase acorn production (Alejano et al., 2008). Additionally, experimental studies conducted in dehesas, mentioned earlier, found that pruning had no significant influence on annual growth of stem circumference (Martin et al., 2010) (Figure 20). Given the results described above, it can be concluded that formative pruning should mainly be recommended for obtaining tall trunks in Cork Oak, and a large crown surface area in both Cork and Holm Oak. Further, maintenance pruning should be avoided unless fuelwood is needed, because it is not clear that it has a positive influence on acorn production, and, on the other hand, it wounds trees, making weak trees particularly vulnerable to pests and diseases. Moreover, it is expensive and involves risks for workers. If practised, maintenance pruning should be light, and cutting off large branches (more than 10 cm in diameter) must be avoided.

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28

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24 20 16 12 8 4 0 2004 NO PRUNING

2005 LIGHT PRUNING

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2010 PLOT MEAN

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Figure 20. Effects of pruning on annual stem circumference growth ± SD in a Quercus ilex dehesa (southwestern Spain).

Regeneration Regeneration is a major issue because natural seedlings are destroyed by grazing, tillage and brush clearing. Indeed, lack of regeneration may be considered the main threat to dehesas as a sustainable agroforestry system. Management practices need to focus actively on this issue. According to Montero et al. (1998), forest regeneration treatments should be applied to one seventh of each management unit for a 20-year period to achieve sufficient regeneration. This way, tree cover would be progressively renewed across the whole unit over a 140-year rotation, and a balanced age distribution would be achieved (Marín-Pageo and DomingoSantos, 2011). Lastly, fencing is the most common way to keep livestock out of regeneration areas. However, when regeneration is being encouraged in small scattered patches, it may be more efficient to use tube shelters or other protective structures for individual trees.

3.2. Pasture and Livestock The main product of the dehesa is livestock, which adds value to the plant production of the agrosilvopastoral system, namely the pasture that is not useful to humans until livestock convert it into animal power and products, such as meat, milk, wool, hides and skins. For this reason, as in every pastoral system, the main objective of the management of the pasture is to maximise the sustainable stocking rate, and in the case of the dehesa this is achieved under extensive conditions, that is, raising livestock on large areas of land, with low stocking rates, and low levels of manpower and of investment in infrastructure, fertilizers, and concentrate or other types of feed not produced within the system itself. In the following section, we describe the types and characteristics of the dehesa pasture and the livestock it supports.

Pasture of the Dehesa Pasture refers to any natural or artificial plant production that provides food to livestock, whether browse, herbage or mast (Ferrer et al., 2001; SECF, 2005). In the dehesas, the shrub Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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layer has been removed, leaving a herb layer and trees, generally composed of a low density of holm and cork oaks. Under these conditions, the grassland covers a large area and benefits from the tree layer, but has uneven production, due to the summer droughts, characteristic of the Mediterranean climate, and to winter conditions, the lowest temperature varying from year to year. Accordingly, most of the production occurs in the spring and to a lesser extent in autumnwinter. In the absence of the shrub layer, the only woody pasture available is tree browse, eaten by livestock when there is little or only poor quality forage in the herb layer. In the high forest dehesas, hardly any of this browse is accessible to livestock, except when humans leave it on the ground after pruning. The fruit of the oaks, the acorn, that in autumn-winter can greatly contribute to the diet of livestock, is often reserved for the Iberian pig, as this is the species that is most efficiently converted into high added-value products. Grassland, the main source of food for ruminants of the dehesa, can be divided into natural pastures, on the one hand, and crops and sown pastures, on the other. Natural pastures can be classified into various groups, as a function of their phenology, species composition, quality and level of production, factors that determine their use. Specifically, according to San Miguel (1994, 2001), the following main types of grassland can be found in most of dehesas:

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- Therophytic Grasslands This type of grassland is mainly composed of annual grass species that pass the summer as seeds. They are spread across most of the dehesa area. Growth occurs in spring and to a lesser extent in autumn; in summer there is no growth at all, and winter growth depends how low the temperature falls. The quality of these pastures is good while they are green, but is rapidly lost when they flower, produce seeds and dry up. - Agrostis Grasslands These are located in areas of dehesa where, given the topography, the soil has other sources of water besides precipitation, generally in thalwegs. Due to the higher soil moisture content, Agrostis grasslands have a delayed phenology and hence remain green for longer, compared to the neighbouring therophytic grasslands, the quality of which rapidly falls at the end of the spring. The most common species in this type of grassland is Agrostis castellana. - Sheepfold Grasslands These are the highest quality pastures in the dehesa, they develop from some of the aforementioned types and are located in favourite places for livestock, where animals gather to rest. In these places, there is an additional input of nutrients, given the accumulation of livestock droppings, animals leaving behind more nutrients per unit area than foraged in this type of grassland. Accordingly, these soils become more fertile, enriched with organic matter and, therefore, develop a higher water holding capacity, and this enables herbaceous perennial species to grow. These grasslands are composed of grasses and legumes that are well-adapted to grazing, of high nutritional quality, and small in size but with a high production; their period of active growth is mainly in spring and autumn, but is longer than that of neighbouring therophytes. The most common species are Poa bulbosa and Trifolium subterraneum.

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Artificial herbaceous grasslands are developed in the dehesa for two main reasons: To avoid the proliferation of the shrubs: In some dehesas this is exclusively achieved using livestock, which remove all the species poorly adapted to grazing, among them all the woody species, and therefore maintain an exclusively herbaceous pasture suitable for grazing by livestock. In other cases, however, this is not possible, as the stocking rate required to prevent the growth of shrubs would be too high for extensive management and to allow regeneration of the tree layer. In such cases, man has to control the serial invasion by shrubs, by regular ploughing or brush clearing, to protect herbaceous grasslands. As recommended by González and San Miguel (2004), ploughing should be followed by seeding.

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To introduce higher quality herbaceous grasslands and thereby obtain herbaceous biomass when there is no production of natural pasture. Subterranean clover (Trifolium subterraneum) is commonly sown as pasture in order to improve the quality of natural grasslands. This species is well-adapted to the soil and climate of dehesas, and provides protein to the livestock, both in early and mid-spring (when the herbaceous biomass is consumed) as well as during late spring (when the seeds are eaten). As an alternative forage for summer and winter, other species are sown, in particular cereals: rye for consumption as grass in winter, and barley, oats, an oats-vetch mixture or triticale to be consumed once seeded, at the beginning of the summer. Since the soils of the dehesas are poor, it is not possible to have crops every year and it is best to leave the land fallow for some time between crops. Traditionally, the cultivated areas are managed following a system referred to as “los cuartos” (meaning, “the quarters”), which consists of dividing a plot into four or more parts of a similar area, and sowing in just one of them each year, while the others lie fallow. What is known as “posío” appears in the uncultivated areas; this is therophytic pasture, mostly species of the Bromus genus, and the soil becomes well covered. The system both provides as an artificial pasture or crop, with winter and summer production, and avoids the invasion of heliophytic shrubs.

Livestock Dehesas have traditionally been used for extensive farming of autochthonous breeds and combining various species (San Miguel, 2001): Sheep: the main breed used was Merino sheep, kept under the transhumance system, and these provided wool and meat; Cattle: used as draught and working animals; Goats: used for clearing vegetation and milk production; Iberian pig: optimal species (and breed) to take full advantage of the acorns and provide meat. In this way, the exploitation of this land was very well adapted to the production of green grass in the dehesa and was compatible with the regeneration of the tree layer. In particular,

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sheep is the species best able to exploit the relatively small and low production Mediterranean pastures, transhumance being used to avoid excessive tree browsing and the need to supply feed in the event of a lack of natural food in the dehesa. Nowadays, many dehesas are used for standing cattle with autochthonous mothers and bulls of improving breeds (commercial crosses), as there is great demand and market for the product, calves for meat, and the management is relatively easy. This practice is not, however, very compatible with the natural regeneration of the tree layer, and therefore with sustainability of the system. Cattle are browsers, with great strength and reach, eating seedlings and wounding saplings. Further, they have high nutritional requirements, given their long period of lactation (six months), and this makes the supply of food from outside the farm necessary for many months of the year, meaning that the production is no longer truly extensive in nature. Sheep continue to be kept as the main livestock on some dehesas, but in most cases are now farmed only semi-extensively, given that instead of ewes lambing once a year, a system of three lamb crops in two years is used, and transhumance is no longer practiced, so they need supplementary feeding. Finally, a considerable area of dehesa is dedicated to raising the Iberian pig, feed on acorns in the period before slaughtering, providing meat of great quality, in particular what is known as “jamón ibérico de bellota”, Iberian cured ham from acorn-fed pigs.

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Debazac, E.F. 1983. Temperate broad-leafed evergreen forest of the Mediterranean region and Middle East. In: Ovington, J.D. (ed.) Ecosystems of the world 10: Temperate broadleaved evergreen forests. Elsevier. Amsterdam, pp.107-123. Díaz, M., Campos, P., Pulido, F.J. 1997. The Spanish Dehesas: a diversity in land use and wildlife. In: Pain, D.J,, Pienkowski, M.W. (eds). Farming and birds in Europe. The common agricultural policy and its implications for bird conservation. Academic Press, San Diego, pp 178- 209. Díaz-Fernández, P.M., 2000. Variabilidad de la fenología del ciclo reproductor del Quercus suber L. en la Península Ibérica. Tesis doctoral. UPM. Madrid. Domingo-Santos, J.M., 2002. Caracterización de suelos forestales de la provincia de Huelva. Ph.D Thesis, E.T.S.I. Montes (UPM). Vol.1 467 pp.; Vol.2 115 pp. [on line] . Domingo-Santos, J.M., Corral Pazos de Provens, E., Fernández de Villarán San Juan, R., Redondo Salguero, R., Roda Oliveira, J.C., Malia Alba, S. 2006. Caracterización de suelos forestales de la Hoja del MTN 1:50.000 Nº 959 “Calañas”. Technical Repport. Grupo ENCE - Universidad de Huelva. Unpublished. Domingo-Santos, J.M., Corral Pazos de Provens, E., Fernández de Villarán San Juan, R., Redondo Salguero, R., García Moreno, J.D. 2010 a. Caracterización de suelos forestales de la Hoja del MTN 1:50.000 Nº 916 “Aroche”. Technical Repport. Grupo ENCE Universidad de Huelva. Unpublished. Domingo-Santos, J.M., Corral Pazos de Provens, E., Fernández de Villarán San Juan, R., Redondo Salguero, R., López Fernández-Cano, H. 2010 b. Caracterización de suelos forestales de la Hoja del MTN 1:50.000 Nº 958 “Puebla de Guzmán”. Technical Repport. Grupo ENCE - Universidad de Huelva. Unpublished. Domingo-Santos, J.M., Corral Pazos de Provens, E., Redondo Salguero, R., Fernández de Villarán San Juan, R., Alejano Monge, R. 2010 c. Carbono orgánico en suelos de las dehesas de la provincia de Huelva. Actas del IV Congreso Ibérico de la Ciencia del Suelo: El suelo: Funciones y Manejo. Sociedad Española de Ciencias del Suelo. Granada, 21-24 septiembre, 2010 Domingo-Santos, J.M., Corral Pazos de Provens, E., Fernández de Villarán San Juan, R., Redondo Salguero, R., López Fernández-Cano, H. 2011. Caracterización de suelos forestales de las Hojas del MTN 1:50.000 Nº 938 “Nerva” y Nº 960 “Valverde del Camino”. Technical Repport. Grupo ENCE - Universidad de Huelva. Unpublished. Ezquerra, F.J. 2009. Los sistemas de dehesa en la Península Ibérica: reflexiones acerca de su génesis, historia, dinámica y gestión. 5º Congreso Forestal Español. SECF- Junta de Castilla León. URL: www.congresoforestal.es REF- 5CFE01-024. FAO., 1993. Conservation of forest genetic resources in tropical forest management. Principles and concepts. FAO Forestry Paper, 107. FAO. Roma. Fernández-Martínez, M. 2011. Caracterización de las principales especies de la Dehesa andaluza. La encina (Quercus ilex L.). In: Alejano, R., Domingo, J., Fernández-Martínez, M. (Eds). Manual para la Gestión Sostenible de la Dehesa Andaluza. Foro EncinalUniversidad de Huelva. Huelva, Spain. Fernández, M., Alejano, R., Dominguez, L., Tapias, R. 2008a. Temperature controls cold hardening more effectively than photoperiod in four Mediterranean broadleaf evergreen species. Tree Forest Science and Biotechnology 2 (1):43- 49.

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Fernández, P., Carbonero, M.D., Blázquez, A. 2008b. La dehesa en el norte de Córdoba. Perspectivas para su conservación. Servicio Publicaciones Universidad de Córdoba. Spain. Fernández, P., Porras. C.J. 1999. La Dehesa: algunos aspectos para la regeneración del arbolado. Consejería de Agricultura y Pesca. Junta de Andalucía. Sevilla, pp 42. Ferrer, C., San Miguel, A., Olea, L., 2001. Nomenclátor básico de pastos en España. Pastos XXXI (1), pp. 7-44. Font Quer, P. 1953. Diccionario de Botánica. Editorial Labor. Barcelona. Gallardo, J.F., Martín, A., Moreno, G., Santa Regina, I., 1998. Nutrient cycling in deciduous forest ecosystems of the Sierra de Gata mountains: nutrient supplies to the soil through both litter and throughfall. Ann. For. Sci. 55, 771-784. Garcia-Mozo, H., Gómez-Casero M., Domínguez, E., Galán, C. 2007. Influence of pollen emission and weather related factors on variations in Holm Oak (Quercus ilex ssp. ballota) acorn production. Environmental and Experimental Botany 61:35-40. Gaussen, H., Bagnouls, F. 1953. Saison sèche et indice xérothermique. Université de Toulouse. Gea-Izquierdo, G., Cañellas, I., Montero, G. 2006. Acorn production in Spanish Holm Oak woodlands. Investigación Agraria. Sistemas y Recursos Forestales 15(3):339-354. Gea-Izquierdo, G., Martín-Benito, D., Cherubini, P., Cañellas, I. 2009. Climate-growth variability in Quercus ilex L. West Iberian open woodlands of different stand density, Ann. For. Sci., 66(8), 802. González, L.M., San Miguel, A. (Coord.) 2004. Manual de buenas prácticas de gestión en fincas de monte mediterráneo de la red Natura 2000. Ministerio de Medio Ambiente, Madrid. Greenberg, C.H. 2000. Individual variation in acorn production by five species of Southern Appalachian oaks. Forest Ecology and Management 132: 199-210. Gutierrez, E., Campelo, F., Camarero, J., Ribas, M., Mutan, E., Nabais, C., Freitas, H. 2011. Climate controls act at different scales on the seasonal pattern of Quercus ilex L. stem radial increments in NE Spain. Trees. 25: 637-646. Healy, W.M., Lewis, A.M., Boose, E.M. 1999. Variation of red acorn production. Forest Ecology and Management 116: 1-11. IPCC. 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. CoreWriting Team, Pachauri R.K. and Reisinger A. (Eds.). IPCC. Geneva. Switzerland. IUSS Working Group WRB. 2006. World reference base for soil resources 2006. World Soil Resources Reports No. 103. FAO, Rome. Junta de Andalucía, 2005. http://www.juntadeandalucia.es. Koenig, W.D., Knops, J.M.H., Carmen, W.J., Stanback, M.T., Mumme, R.L. 1994. Estimating acorn production using visual surveys. Canadian Journal of Forest Research 24: 2105-2112. Larcher, W. 2003. Physiological Plant Ecology, 4th ed. Springer. Berlin 513 pp. Lo Gullo, M., Salleo, S., Rosso, R., Trifilò, P., 2003. Drought resistance of 2-year-old saplings of Mediterranean forest trees in the field: relations between water relations, hydraulics and productivity. Plant Soil 250, 259-272.

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Marín-Pageo, F. , Domingo-Santos J.M., 2011. Características dasocráticas. In: Alejano, R., Domingo, J., Fernández-Martínez, M. (Eds). Manual para la Gestión Sostenible de la Dehesa Andaluza. Foro Encinal- Universidad de Huelva. Huelva, Spain. Martín, D., Alejano, R., Vázquez-Piqué, J., Tapias, R. 2010. The stem growth of Quercus ilex subs. ballota (Desf.) Samp. and Quercus suber L. in the province of Huelva, Spain. Influence of climate, soil, silvicultural and spatial parameters. Worlddendro 2010 the 8th International Conference on Dendrochronology. Metla, Finland, 270-270. Martín D., Carevic F., Vázquez-Piqué J., Alejano R., 2010b. Does acorn production influence the diametric stem growth of Holm Oak? Worlddendro 2010, the 8th International Conference on Dendrochronology. Metla. Finland, 109-109. Martin, A., Infante, J.M., García, J., Merino, J., Fernández, R. 1998. Producción de bellotas en montes y dehesas del Suroeste Español. Pastos XXVIII, 2: 237- 248. Mediavilla, S., Escudero, A., 2009. Ontogenetic changes in leaf phenology of two cooccurring Mediterranean oaks differing in leaf life span. Ecol. Res., 24: 1083-1090. Ministerio de Medio Ambiente. 1997. Segundo Inventario Forestal Nacional. Dirección General de Conservación de la Naturaleza. Organismo Autónomo de Parques Nacionales. Madrid. Misson, L., Degueldre, D., Collin, C., Rodriguez, R., Rocheteau, A., Ourcival, J.M., Rambal, S., 2011. Phenological responses to extreme droughts in a Mediterranean forest. Global Change Biol. 17, 1036-1048. Mitrakos, K. 198). A theory for Mediterranean plant life. Acta Oecol 1:245-252. Montero, G., San Miguel, A., Cañellas, I., 1998. Sistemas de selvicultura mediterránea. La dehesa. In: Jiménez, R., Lamo, J. (Eds.), Agricultura sostenible. Agrofuturo-Life-Mundiprensa, Madrid, pp. 519-554. Navarro, R., Fernández, P., 2002. El síndrome de la seca del encinar.Propuesta de soluciones para el valle de Los Pedroches. Fundación Ricardo Delgado Vizcaíno, Pozoblanco, Spain. Nijland, W., Jansma, E., Addink, E. A., Domínguez Delmás, M., De Jong, S. M. 2011. Relating ring width of Mediterranean evergreen species to seasonal and annual variations of precipitation and temperature. Biogeosciences, 8, 1141-1152. Ogaya, R, Penñuelas, J, Martinez-Vilalta, J, Mangiron, M. 2003. Effect of drought on diameter increment of Quercus ilex, Phillyrea latifolia, and Arbutus unedo in a Holm Oak forest of NE Spain. For. Ecol. Manag. 180:175–184. Ogaya, R, Peñuelas, J. 2003. Comparative field study of Quercus ilex and Phillyrea latifolia: photosynthetic response to experimental drought conditions. Environ. Exp. Bot. 50:137– 148. Palmarev, E. 1989. Paleobotanical evidences of the Tertiary history and origin of the Mediterranean sclerophyll dendroflora. Plant. Syst. Evol. 162:93-107. Pena-Rojas, K., Aranda, X., Joffre, R., Fleck, I. 2005. Leaf morphology, photochemistry and water status changes in resprouting Quercus ilex during drought. Funct. Plant. Biol. 32:117–130. Pérez-Ramos, I.M., Ourcival, J.M., Limousin, J.M., Rambal, S., 2010. Mast seeding under increasing drought: results from a long-term data set and from a rainfall exclusion experiment. Ecology 91, 3057-3068. Pérez-Soba, M., San Miguel, A., Elena-Rosselló, R. 2007. Complexity in the simplicity: The Spanish Dehesas. In: Pedroli B., Van Doorn, A., De Blust, G., Paracchini, M.L.,

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Wascher, D., Bunce, F. (Eds.) Europe’s living landscapes. Essays on exploring our identity in the countryside. LANDSCAPE EUROPE/KNNV. Pesoli, P., Gratani, L., Larcher, W. 2003. Response of Quercus ilex from different provenances to experimentally imposed water stress. Biol. Plantarum. 46:577–581. Poblaciones, M.J., López-Bellido, R., Olea, L., Benito, C. 2006. Evaluation of the production of acorns of oaks (Quercus ilex L. ssp. ballota) from Southwest of Extremadura, Spain. In: Mosquera, M.R., McAdam, J., Rigueiro, A. (Eds). Silvopastoralism and Sustainable Land Management. CABI Publishing. Oxfordshire, UK. Rivest, D., Rolo, V., Lopez-Diaz, M.L., Moreno, G. 2011. Belowground competition for nutrients in shrub-encroached Mediterranean dehesas. Nutr. Cycl. Agroecosyst. 90:347– 354. Rodá, F., Retana, J., Gracia, C.A., Bellot, J., 1999. Ecology of Mediterranean evergreen oak forests. Springer. New York. Ruiz de la Torre, J. 2006. Flora Mayor. Organismo Autónomo de Parques Nacionales. Ministerio de Medio Ambiente. Madrid. San Miguel, A. 1994.La dehesa española: origen, tipología, características y gestión. Fundación Conde del Valle de Salazar. Madrid. San Miguel, A., 2001. Pastos naturales españoles. Caracterización, aprovechamiento y posibilidades de mejora. Coedición Fundación Conde del Valle de Salazar. MundiPrensa. Madrid. Sayer, E.J., 2006. Using experimental manipulation to assess the roles of leaf litter in the functioning of forest ecosystems. Biol. Rev. 81, 1-31. SECF 2005. Diccionario Forestal. Sociedad Española de Ciencias Forestales-Mundi-Prensa, Madrid. Serrada, R., San Miguel, A. 2008. Selvicultura en dehesas. En: Serrada, R., Montero, G., Reque, J.A. Compendio de Selvicultura aplicada en España.INIA- FUCOVASA. Madrid. Serrano, L., Peñuelas, J. 2005. Contribution of physiological and morphological adjustments to drought resistance in two Mediterranean tree species. Biol Plantarum 49:551–559. Siscart, D., Diego, V., Lloret, F. 1999. Acorn Ecology. In: Rodà, F., Retana, J., Gracia, C.A., Bellot, J. (Eds.) Ecology od Mediterranean evergreen oak forests. Springer Verlag. Berlin, pp. 75-86. Smith, C.C., Fretwell, S.D. 1974. The optimal balance between size and number of offspring. American Naturalist 108: 499-506. Thirgood, J.V. 1981. Man and the Mediterranean Forest, a history of resource depletion. Academic Press. London. Tognetti, R., Giovanelli, A., Longobucco, A., Miglietta, F., Raschi, A. 1996. Water relations of oak species growing in the natural CO2 spring of Rapolano (central Italy), Ann. Sci. For. 53: 475–485. Wilbur, H.M. 1977. Propagule size, number and disperssion pattern in Ambystoma and Asclepias. American Naturalist 111: 43-68. Zhang, S. H., Romane, F.1991. Variations de la croissance radiale de Quercus ilex L. en fonction du climat, Ann. Sci. Forest., 48, 225–234.

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In: Oak: Ecology, Types and Management Editors: C. Aleixo Chuteira and A. Bispo Grão

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Chapter 4

OAK WOOD José A. Santos1, João P. F. Carvalho2 and Joana Santos1 1

2

National Laboratory of Energy and Geology, Lisboa, Portugal University Tras-os-Montes Alto Douro, Department Forestry, Vila Real, Portugal

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ABSTRACT Oak timber is valuated for its beauty, good mechanical properties and natural durability and may have multiple uses. An understanding of the properties of oak timber and the elements that characterize wood quality is essential for its proper use. It is important to have quality control of physical, mechanical and technological wood characteristics in order to define the better primary processing and end-use. The chapter gives a characterization of oak wood with regard to chemical, physical and mechanical wood properties. Results on the wood primary processing are provided and information addressing proper technical procedures for wood sawing and drying. Appropriate timber processing techniques are described in order to obtain lumber with a good dimensional stability, avoiding cracks and warping. Adequate wood classification is required in order to optimize industrial processes and improve product quality. Quality criteria and procedures for round and sawtimber classification are referenced, and survey results concerning oak wood grading are showed. Indications of the use of oak wood for various applications are given.

INTRODUCTION The oak wood is valued for its beauty, good mechanical properties and durability. It can have many uses such as in carpentry, construction, furniture, veneer, flooring, cooperage, charcoal production and fuelwood. Oak wood is very appreciated and widely used in many applications because of its heritage, beauty, strength and natural durability. Oak wood is a renewable resource and one of the most important construction materials. Wood retains carbon, is biodegradable, allows a variety of applications and requires less energy to manufacture. Interest in both economic and ecological value of oaks will continue

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and probably increase in the future. Their relevance for multiple-purpose forest management as well high value timber supply is of great importance. Only knowing the wood characteristics and properties can we set specific uses. Different studies have defined applications that allow an increment value of oak wood. Optimized wood processing and quality control criteria were also developed. The wood chemical, physical, mechanical and technological characteristics of the oak species may be crucial to encouraging the installation of certain forest stands by forest owners and managers, including indigenous oak species. The impregnated product durability and preserving natural features are also to be taken into account in the selection of certain woods. The awareness and appreciation of wood physical, mechanical and technological features are therefore important to use and promote oak wood at an industrial level, for its best use and quality. In addition to the species variability, the physical, mechanical and technological properties also depend on the site quality and management practices. Implementation of good forestry practices is important to achieve quality wood and desired size.

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1. OAK WOOD CHARACTERIZATION The wood is the ligneous material forming trunks, branches and roots. The industrial interest is taken from the stems because of their size, regularity and features. The variety of species is also reflected in an infinite variety of physical, mechanical, chemical and technological properties of the wood. These differences in properties will cover a huge range of different preferred uses, from requirements of duration and high resistance to the decorative aspect and behavior in service. Thus, various types of combinations between the various parameters can be found. The analysis of the timber characteristics is fundamental and extremely important for the profitability of wood transformation processes, definition of uses preferred, and most appropriate processing technology.

1.1. Description and Structure of the Wood 1.1.1. Wood Structural aspect and Anatomy The structure of the oak wood consists of various types of cells, being far more complex than the conifer species (Farmer, 1981). The description of the anatomical structure can be made macro or microscopically. In the transverse plane we can identify the growth rings and pores. The growth rings can be identified in the transverse plane, which result from sectioning of straight timber vessels. In the radial and tangential planes it is possible to view the parenchyma and xylem rays. The description of the structural aspect is made from the peculiarities observable in cross section, usually at the top of the logs. The newly formed and physiologically active wood, which is the outer layers of the tree, is the sapwood. After a certain age, depending on the species and ecological conditions, a zone of darker color can be seen which constitutes the heartwood.

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Figure 1. Transversal section of an oak log with a distinctive view between heartwood and sapwood.

White oak species normally presents a star pith, and a distinctive heart with a regular and defined contour, and yellowish-brown color. The sapwood has yellowish-white color. The difference between heartwood and sapwood is well contrasted in fresh sawn timber. The growth rings are very distinct due to the pronounced porous zone with a well defined and regular contour. Their pattern is described as ring porous and is common in other hardwood species (Kollmann et al., 1975). The majority of oak species follow this pattern although few such as the Q. fenestrate, an Indian evergreen oak, are diffuse-porous. The texture is associated with the intensity of the transition between the early and late wood, which results in heterogeneity of the material in terms of mechanical behavior, as well technological, mechanical and laboring characteristics of the wood. The grain is also a very important aspect for the identification through the longitudinal arrangement of fibrous elements. In most white oaks the grain is straight. The wood pattern is provided by tangential layers of growth layers and the ligneous rays. The wood of oaks consists of vessels, also known as pores, the trachea, various types of fibers, woody parenchyma cells oriented longitudinally and the xylem rays (Figure 2). The wood porosity in oaks has a ring distribution, because the vessels that form in the early wood are much wider than those formed in late wood. The vessels have a circular to oval shape and communicate with each other through a perforation plate. The early wood consists of sets of 2 to 3 large pores, while the final wood has pores invisible to the naked eye, disposed radially in more or less rectilinear bands.

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Figure 2. Oak wood structure. TT: transverse section; RR: radial section; TG: tangential section; P: vase; SC: perforation plate; F: wood fiber; K: punctuation; MR: wood ray; AR: annual ring; S: early wood; SM: late wood; ML: middle lamella.

The parenchyma cells surrounding the vessels at the end of a particular season secrete tyloses or other amorphous exudates filling the vessels that will make them useless. The tyloses are easily identifiable and inhibit the penetration of preserving chemicals (Figure 3). Wood studies showed that oak species such as the common oak (Quercus robur), white oak (Q. alba) and pyrenean oak (Q. pyrenaica) have many tyloses making them suitable for cooperage, while other oak species such as the northern-red oak (Q. rubra) and other red oaks does not have tyloses (Wilson and White, 1986). The heartwood of white oak has a high natural decay resistance, while that of red oak is low.

Figure 3. Vases and tyloses in Pyrenean oak wood. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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The fibers are long and narrow cells similar to the tracheids, and are only present in hardwoods. Oaks may have libriform fibers, fibre-tracheids and vasicentric tracheids. The distinction between these relates to the nature of corrosion, i.e., the tracheids have bumps with well defined outlines while others have simple bumps. Libriform fibers are smaller than the tracheids, either in length or in diameter, having a narrow lumen (Carvalho, 1997). Its main function is to keep the tree standing but may also participate in conducting of the sap. All oaks have rays in transversal section. In some oaks the rays are very extensive and remarkable. They may begin at any ring, but once formed continue to grow until the bark and may even enter into this.

1.1.2. Chemical Properties The sapwood is composed of living cells that accumulate carbohydrates and occupy about 10 to 40% of the total volume. In contrast, the heartwood the cells are dead and usually darker resulting from the production and secretion of substances with accumulation of reserves. Some studies showed that the chemical composition of wood varies greatly depending on the part of the tree (roots, trunk and branches), the type of wood, geographical location, climate and soil where the tree grows. The main chemical elements present in the wood are carbon (C), hydrogen (H), oxygen (O) and a small percentage of nitrogen (N). These main elements are combined to give rise to major organic constituents of wood: cellulose, hemicelluloses and lignin. The xylem is a tissue composed of various organic polymers which are molecules made of many repeated subunits. The cell wall of the xylem has the basic structure of cellulose, which is a linear molecule of sugar or a polysaccharide, composed of several molecules of glucose. These cellulose polymers comprise about 40 to 45% of the dry weight of most woods. Cellulose is a substance of the skeletal complex woody structure with high tensile strength. The hemicelluloses is formed of many combinations of various monosaccharide (glucose, galactose, xylose, arabinose and mannose) linked by different glucosidic linkages. Although similar to cellulose differs from this especially in conformation, degree of polymerization and molecular weight. Hemicelluloses have multiple functions in regulation of cell wall consolidation and in determining its properties. The percentage of this constituent in oaks is about 15 to 35%. The third major constituent of wood is lignin, a complex structure and high molecular weight, which gives the wood characteristic resistance to mechanical stress. It is also responsible for the rigidity of the tree and has an important role in the durability of the wood. It guarantees the firmness of cells to each other thanks to its concentration in the middle lamella, and is produced only by living cells. It is the lignin that allows the differentiation between wood and other cellulosic materials in nature. Lignin content in wood varies from 20 to 35%. Many other chemicals are present in the wood, known generically as extractives (terpenes, resins, polyphenols, tannins, oils, gums, aromatic compounds and salts of organic acids), deposited in the lumens and cell walls. The presence of extractives is higher in the bark and heartwood. When toxic they ensure high resistance to attack by agents of biological degradation. Living cells of rays contain glucose, fructose, saccharose and amide. The extractive content is low, normally about 10% of the dry weight of a normal wood species

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that grows in a temperate climate. However, their nature can influence the choice of wood for a particular purpose.

1.1.3. Physical Properties

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Density The wood density is highly dependent on moisture, especially for values above the fiber saturation point, since it makes change the weight as the volume of the wood. Wood density is normally analyzed for a water content of 12%. The wood density depends on the species, however, trees of the same species may have very different density values. This feature varies depending on the season and type of cultural treatment, which will influence the thickness of growth rings and the proportion of tissues that constitute the annual layer (Santos et al., 2005). This physical property provides information on other general characteristics of wood, including the ease of drying, mechanical strength, natural durability and permeability. Physical and mechanical properties vary widely between trees and inside each tree. Different studies showed that there is an important genetic variability inside each population for site factors and wood quality (Polge; 1973; Nepveu, 1984). Wood density has a major influence on lumber behaviour and affects other quality characteristics (strength, durability, shrinkage). Evidences show that average ring density is positively correlated with ring width (Figure 4). However, studies showed great individual variability, and explaining an important fraction of the existing variability related to wood characteristics (Nepveu, 1991).

Figure 4. Growth ring width and wood density of sessile oak, Q. petraea (from Polge, 1973).

Evaluations made with Pyrenean oak wood from trees harvested in various forests gave an average density of 774 kg/m3 (12% water content). Wood density increases through the stem core with values of 810 kg/m3, while it decreases for the outer zone and upwards the tree stem. This species has, therefore, density values that are classified as moderately heavy to heavy. Wood density for other oak species (Quercus robur, Q. pyrenaica, Q. alba, Q. rubra, Q. faginea, Q. ilex) is also presented in Table 1.

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Shrinkage Wood is a hygroscopic material and always tends to balance its moisture with the humidity of the environment. The loss of moisture from a certain point is accompanied by decrease in size, a process that is known as shrinkage of the wood. The reverse process, where dry wood is placed in a humid environment is called by swelling and is characterized by a volume increase to the point of fiber saturation. The values of variation in size vary according to the direction considered. In the direction parallel to grain size variation is almost null but in the perpendicular direction is very high. The shrinkage is then determined depending on the direction and may be calculated the linear tangential, radial and axial shrinkage. The sum of these three results the value of volumetric shrinkage. Shrinkage varies with species, in general the softwoods have lower shrinkage values than the denser woods. For wood drying, this is a property that allows the evaluation of the wood behavior on the predisposition to warping and cracks, and the changes in volume and shape. Different shrinkage values can be seen in Table 1 for different oak species types. For Pyrenean oak the average shrinkage obtained in tests carried out in the tangential and radial direction are 10.5% and 5.8%, respectively, and the total volumetric shrinkage is 17.4%. Certain oak species such as Q. faginea have high shrinkage values requiring very delicate drying procedures. Water Content The amount of water in wood is strongly influenced by the amount of woody substances per unit volume of material. Therefore, different oak species have different levels in water even considering the same state of moisture. With green wood, where the water is largely free, species that have a higher percentage of water content are those with the greatest amount of cellular cavities. When fiber saturation state is achieved there is no free water and only water soaking exists, being wood density the most important factor. Below the fibers saturation level, remains the direct relationship between wood density and water content. The woods with a lower fibers saturation level stabilize with relatively high moisture equilibrium, but in places where the moisture balance is low these woods deform considerably. On the other hand, the woods with a high fibers saturation level used in situations where the equilibrium moisture content is low are usually little tense about the changes in humidity. The moisture content of wood is a parameter that should be given special attention because it affects the mechanical properties, the degradation by biological agents, and some technological conditions. Thus, the correct specification of the water content depending on the humidity of the environment and stabilization for a given moisture content are aspects that minimize the problems inherent to certain uses. 1.1.4. Mechanical Properties The study of the wood mechanical behavior requires several laboratory tests which are based on defined in standard procedures. The wood for structural purposes (beams, columns and other structures) that supports a given load is usually requested for three kinds of stress:

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tension, compression and bending (Zobel and Buijtenen, 1989). The mechanical tests are performed to the worst possible scenario which determines the maximum forces that may be attached to the wood, allowing the establishment of safe thresholds. Several studies concerning mechanical characteristics of oak wood were performed. These studies mostly regard to cohesion and cross-axial. For axial cohesion, the properties of tensile, compression, and longitudinal or parallel cut; and for the cross-cohesion the properties are tensile, compression and cross-sectional hardness and bending.

Parallel Traction Parallel traction is defined as the ratio of the breaking load by the transversal sectional area. Because wood has a high cohesion in the longitudinal direction this is not a property that requires great attention.

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Parallel Compression The parallel or axial compression is the ratio of the breaking force by the axial crosssectional area of the sample. Os oaks have the particularity of producing a sound before the rupture, which may serve as a warning. Studies performed with some oak species (Q. pyrenaica, Q. robur) reveal an average compression parallel value of 510 and 554 kgf/cm2 (50 and 54 MPa), showing that the wood has a good resistance. Cutting This parameter allows determining the resistance of the wood when subjected to stress only on one side. The tensile strength by cutting corresponds to the ratio between the cutting breaking force and the rupture section of the sample. With Pyrenean oak there were tests of tensile strength parallel to the cutting direction and transverse direction. The average values were 195 and 130 kgf/cm2 (19 and 13 MPa), respectively. These values are higher than the usually reported for two widely used wood, pine and fir, which have parallel cutting values of the order of 18 and 10 MPa, respectively. Transversal Traction The transversal traction is defined as the ratio of the breaking strength by the section area. It attempts to measure the transversal cohesion. In wood, the transversal traction is the mechanical property which is more fragile. The weak transversal strength as a consequence of the fact that wood is not always supporting the stresses caused by dimensional variations due to changes in water content, which can cause superficial or internal small cracks. In the process of drying the surface of the wood has a moisture content lower than inside, which may result in transversal traction that exceeds the limits of the wood itself. Transversal Compression Perpendicularly to the wood fibers the mechanical strength is very weak hence the resulting values of this test are lower than those obtained by the parallel compression test. Hardness Hardness is a measure of the resistance to foreign bodies in the wood. This resistance is greater in the axial direction and the differences between the values obtained in the radial and Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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tangential directions are rarely significant. This property is related to the abrasion strength, scratching with various objects, and the difficulty of woodworking tools. Their determination is important for certain types of uses such as flooring, furniture or pencils.

Static Bending The static bending is a very important property because most of the wooden structures are subject to bending loads that cause them curvatures. The bending refers to the axial direction and its value is often called the modulus of rupture. Tests carried out with Pyrenean oak wood showed an average value of 96 MPa. Dynamic Bending The dynamic bending is related to the strength of wood when subjected to sudden loading, in contrast to the bending, presented earlier, where the loads are static or slowly applied. The assessment of this property is particularly important for a particular use that the wood is subject, for example, tools’ handles, sports equipments or boxes. Apparent Modulus of Elasticity The wood has usually a very high elasticity compared with other materials, with a high degree of deformation and maintaining a significant recovery level of its dimensions. The higher the apparent modulus of elasticity (AME) the greater the resistance and the resilience module, i.e., the ability of the material to absorb energy in the elastic range. Table 1. Average physical and mechanical properties of oak species (AME – Apparent Modulus of Elasticity

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Species

Q. robur

Q. pyrenaica

Q. alba

Q. rubra

Q. faginea

Q. ilex

Physical properties Density (kg.m-3)

710

774

680

750

890

900

Tangential shrinkage (%)

10.7

10.5

8.8

11.0

14.9

9.5

Radial shrinkage (%)

4.9

5.8

4.4

4.4

9.5

5.3

Volumetric shrinkage (%)

16.8

17.4

12.7

16.3

25.0

16.0

Fiber saturation point (%)

31

30

n.a.

32

n.a.

27

Transverse compression (MPa)

n.a.

14.5

7.4

n.a.

n.a.

n.a.

Transverse tension (MPa)

3.9

8.3

5.5

4.3

4.9

4.6

Rolling shear (MPa)

n.a.

12.8

n.a.

n.a.

n.a.

n.a.

Mechanical properties

Parallel tension (MPa)

n.a.

84.0

n.a.

n.a.

n.a.

n.a.

Bending strength (MPa)

135

138

105

152

150

147

AME (MPa)

n.a.

11500

12300

n.a.

n.a.

n.a.

Parallel shear (MPa)

n.a.

19.1

13.8

n.a.

n.a.

n.a.

Parallel compression (MPa)

50.5

54.3

51.3

54

53.0

50.0

The AME is different in all three directions (axial, radial and tangential), although there is no great difference between the radial and tangential directions. Typically, the test is best Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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used for static bending and average values of 11.220 MPa were found for the Pyrenean oak wood. Physical and mechanical characteristics of different oak species are presented in Table 1 (Carvalho, 1997; Forest Products Laboratory, 1999; Santos et al., 2005). The values for Pyrenean oak were obtained in a research project whit sample trees from oak forests located in Portugal (Carvalho et al., 2005; Santos et al., 2005). Samples were taken from the heartwood to the sapwood and from the bottom of the stem to the upper zone. One interesting characteristic of the Pyrenean oak wood was that the bending module of elasticity is lower than other oak species of the same density but on other side it deforms significantly in bending before breaking. This could be interesting when making curved components in carpentry and furniture.

2. INDUSTRIAL PROCESSING - PREPARATION OF WOOD FOR

INDUSTRIAL USE

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The preparation of the wood for industrial use includes all actions taking in mind a specific final product. Before the cutting in specific dimensions, profiles and joints it is necessary to dry, equilibrate and dimensionally stabilize the wood, which can only be made with a good quality drying. The drying operation is the most important phase of wood technological transformation, and has an important contribution to a better gluing, finishing and conservation operations. Due to the incidence of defects and anisotropy, both morphological and structural, drying of oak species is a slow and delicate operation. The heartwood of oaks is very difficult to impregnate artificially, but in general they have high natural good conservation.

2.1. Sawing Sawing is one of most important phases of transformation of wood taking into account not only the aesthetic aspect but also the dimensional behavior and strength. Wood comes from a round geometry which causes a great problem when producing flat boards. The sawing concerns the transformation of logs into planks of various thicknesses depending on the intended purpose of that material. The action includes the separation of bark and sapwood. Oaks are species of moderate to high density so it would be supposed having a difficult sawing due to its hardness. Oaks may present poor conformation of the trunks, and when this occur the achievement of long pieces is more difficult. One key point for the quality of any wood piece in all its aspects is the parallelism between edges and the grain direction. Even the drying of wood is influenced by the sawing pattern, several sawing works have showed that an adequate sawing pattern is essential to obtain boards of good quality. In summary the sawing cannot guarantee the final quality but a bad sawing implies a definite loss of quality and increases the processing costs. The sawing into planks of oak wood does not cause any difficulty since it is made in fresh. The sawn can be made with normal blades without need to hardened teeth and causes no wear out of the cutters edges. Usually deformations during sawing of the logs are not

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reported, however it revealed to be appropriate for a better quality of wood, making a first cut at the center of the stem, following the direction of the core.

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Figure 5. Oak wood sawing assessment (Pyrenean oak).

Sawing Patterns The pattern of sawing is the sequence of cutting planes that defines a certain orientation of the growing layers in relation to the faces of the boards. In the Figure 6 it is shown an optimal sequence representing the best compromise between quality and profitability of wood cutting. It is obvious that the sawing with turning of the logs is only feasible when the diameters are bigger than a certain dimension, generally, more than 35 cm. After 1st and 2nd sawing the log is turned 90 º and two more sawing planes are done, 3tr and 4th. Then the log is divided in two halves passing the sawing plane by the pith. Finally the sawn is made into planks in the desired thickness, until the dimensions allow it. This method allows a better alignment of the edge of the wood with the edges of the sawn pieces and a larger number of elements with radial cut. The optimized standard method is only practical in sawing logs with diameters over 35 cm. The oak industrial processing is in all aspects equal to the other species, taking into consideration some difficulty on planning when close to knots that causes deviation of grain direction.

Figure 6. Optimized sequence of sawn for oak.

Quarter Sawing (Radial Boards) Cutting planes are oriented as much as possible perpendicular to annual rings. In boards of small width this method can have a minor inconvenience like a tendency to a deformation Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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named “spring”, i.e., to curve in the edge direction. This is corrected with one more cut and some loss of material. This method produces very fine wood, especially on oak making appear the typical oak draw (bright rays - pith rays pronounced).

Flat Sawn (Tangential Boards) This pattern can occur in certain phases of ordinary sawn, when the sawn plan is tangential to the annual ring. Oak planks cut by this method warp too much and can reveal big checks or splits during drying. Also the difference of shrinkage of sapwood more than the heartwood increase warp and twisting of planks. Tangential sawing boards or planks sawn tangentially to annual rings are not suitable for flooring. Ordinary Sawn In this pattern cutting planes are all parallel to each other. Parallel cuts made throughout the width of the log cutting parallel slices of planks. This is the easiest and economical method. The boards obtained are of all types, radial, tangential and mix, appearing in different widths. If middle planks are put drying entire the manifestation of a deformation named “cup” and checks is inevitable.

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2.2. Wood Drying Oaks are generally classified in the group of species very difficult to dry (Perré et al., 2007). This is caused by the anatomy of oak with the tyloses in the pores, high density and big amount or heartwood. Although it may be a prolonged operation it can be developed successfully if handled carefully. The drying of oak like for all other wood species results from the combination of two phenomena, evaporation and circulation of water in the wood. Initially the drying process is made by evaporation of free water contained in the wood free spaces, so there is no or very little dimensional variation. Below fiber saturation point (FSP), cell walls contracts resulting in a decrease in thickness or width. At this last stage drying of oaks may take several weeks or months. The drying operation is generally made by one or combination of the following two methods: natural drying (in open air); and artificial drying (kiln drying). On the industrial side, air drying has advantages in economic terms, nevertheless it is a relatively slower process of drying. The choice of either type of drying by the industry will always take into account the compromise between these two aspects and will depend on the objectives, the amount of material to dry and their respective characteristics (thickness, size). The mishandling of the drying operation is the main cause of the appearance of cracks, collapse and strong deformations. The wood must be stacked following some rules as the regular thickness and well calibrated stickers, typically 25x25 mm section of a dried hardwood. The stickers must be placed all in the same vertical threading. The spacing between the rows of stacking shall be a maximum of 40 cm, for thicknesses from 27 to 35 mm, but only 20 cm or less for thicknesses less than 25 mm. Weights shall be placed on top of the stacks to prevent the deformation of the boards, especially on the upper layers. Because the water moves more quickly in the axial direction than in the transverse direction, it is advantageous the tops of the pieces have to be

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protected. However water is advantageous for the drying of oak, either rainwater or irrigation water, but water has to reach all surfaces of wood in abundance to allow the cleanup of tannins that can cause dark stains if left to concentrate on specific points.

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2.2.1. Natural Drying The air drying depends on the characteristics of the wood to dry and the environment in which drying takes place, i.e., the atmospheric air. The choice of season of year for the beginning of drying is crucial for the duration of this process. In order to avoid defects caused by too much fast drying the stacks must be placed on no strong wind spaces and avoiding the driest seasons. In hot summers the wood must be moistened. In rainy periods the drying does not go on. After the occurrence of heavy rainfall, the values of water content of wood rapidly return to normal values, following the normal curve of the drying trend. In the formation of air-drying stacks it is absolutely necessary to have air circulation inside the stack but also under it. To achieve this goal it is necessary to elevate sufficiently the stack from the soil about 40 cm. As the wood dries from the surface to the interior, the surface layers of the boards have at the end of drying a value much lower than inside. This must be corrected across an equalization procedure (Carvalho, 2005). Even in the air drying is of great advantage to monitor the moisture content and the values of the probes have to be registered with some frequency.

Figure 7. Open air drying stacks of Pyrenean oak.

Natural drying of Pyrenean oak allowed accurate evaluation of operation costs. Results were quite favorable, but with the disadvantage in thick dimensions 70 mm revealing a very lengthy process, about one year to reduce the moisture content from 75% to 16%. In boards 30 to 35 mm thick it took about 4 to 5 months, example of the stack in Figure 7. Taking into account the characteristics of Pyrenean oak wood it is recommended the use of a mixed process, initiated and controlled by natural drying completed in the kiln dryer (Carvalho et al., 2004). This process allows the use of the advantages of both drying processes, mainly by reducing the drying time of wood for about half and in controlled costs. Figure 8 shows the graph of one trial of air drying of Pyrenean oak.

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José A. Santos, João P. F. Carvalho and Joana Santos Air drying of pyrenean oak - Thickness 35 mm 70

65 60

Moisture content (%)

55 50 45 40 35 30 25 20 15 10 5 0 15-Abr 30-Abr 15-Mai 30-Mai 14-Jun 29-Jun

14-Jul

29-Jul 13-Ago 28-Ago 12-Set

27-Set 12-Out 27-Out

Drying duration

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Figure 8. Air drying of Pyrenean oak.

2.2.2. Artificial Drying The various possible types of artificial drying for oak are conventional dryer, vacuum, dehumidifying dryer in and still a solar dryer (Cividini, 2001). Kiln dryers are conducted in modern controlled process done automatically by electrical probes that record the moisture content of wood throughout the drying cycle and impose the evolution of temperature and relative humidity in accordance with a pre-established program. Drying of oak wood should be carried slowly and at relatively low temperature (40 ºC to 60 ºC) and a gradient less than 2.3 (Santos et al., 2005). The experiments revealed that this type of drying takes a month and a half to dry a board 45 mm thick, from green (75%) to 12% moisture content, and about 20 days to thinner thicknesses. The placement of the wood inside the dryer has to respect some basic rules: leave a gap between the wood and the walls on the direction of air flow, a distance equal to the sum of the air passage openings between the boards, i.e., a distance equal to the thickness of the stacking rules times the number of layers. On the other hand, it cannot be let any air passage laterally, superiorly and inferiorly to the pile. If not possible totally fill the dryer they must be closed all the air vents with plywood or other material resistant to moist and heat. The process follows the drying programs previously defined. To this end, the dryer must have systems for measuring temperature, relative humidity, or alternatively, the equilibrium moisture content of wood, and several probes measuring the wood moisture content. The system automatically controls temperature, humidity, speed and direction of rotation of the fans and the opening of the chimneys to the outside. Concerning the total energy consumption theoretically the heat pump dehumidifier is less than conventional dryer, but the costs depend mainly on the prices of electricity, cost of equipment, maintenance and depreciation. The reconciliation of such a pre-drying with air drying will reduce the drying costs. 2.2.3. Drying Defects Drying defects are well characterized for all species, namely: moisture content gradient difference between moisture in the surface and in the interior of the boards; distortions change in the board geometry; casehardening - internal stresses different in different layers in the same board; collapse - excessive shrinkage; internal checks - holes in the interior of the

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Oak Wood

boards. Some of these defects are interrelated, for example collapse and internal checks (McMinn and Stubbs, 1985; Neumann and Saavedra, 1992). The collapse generally defined as an abnormal form of shrinkage occurring above fiber saturation point can occur in different degrees of intensity (Innes, 1995). Moderate collapse is revealed by wavy surfaces, mainly in radial cutting boards. Unevenly corrugated board surface is cited in bibliography as the main macroscopic characteristic (Figure 9-b). If collapse is more intense it appears associated to gross distortions and/or internal checking, usually in back-sawn boards (Figure 9-c).

(a)

(b)

(c)

(d)

(e)

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Figure 9. Possible defects of kiln drying: (a) moisture gradient; (b) collapse on radial boards; (c) internal checks on tangential boards; (d) casehardening; (e) distortions.

The main explanation referenced as the cause of collapse is the hydrostatic tension. Above the fiber saturation point the cohesive forces of the water leaving the wood pulls the wet cell walls together. A too high drying temperature before reaching the fiber saturation point is also an aggravating factor. While some authors attributes the tendency to collapse to the weakness of parenchyma wall or thin-walled fibers, other authors tried to correlate the tendency to collapse with the density of the species (Perré et al., 2007). It was reported to the laboratory of wood technology (LNEG) many occurrences of collapse in oak kiln drying, including with presence of internal cracks (honeycombing), identified its origin as a bad drying procedure for this species.

Moisture and Quality Testing Procedure

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The evaluation of internal drying stresses were identified in technical terms as “casehardening” made by the two usual methods, the prong test (Figure 10), and the slice test (Figure 11). The cuts from boards were taken from three different length locations; near the top, middle distance to the centre of board and near centre - A3 in Figure 10.

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Figure 11. Methods for evaluation of internal drying stresses: (a)- prong test; (b)-slice test.

2.2.4. Control of Collapse Collapsed wood is almost impossible to process in machines, specially the planing and thickness operations, but also drilling, driving nails and sawing (Siau and Meyer, 1966; Chong and Barnes, 1969; Barreal, 1988; Duarte, 1992). The hardness of collapsed wood is very strongly increased as much as the density. So, additionally to the surface ripple in quarter sawn boards we have also the density, as practical indicators to visually indentify collapse presence. In studies on Pyrenean oak it was concluded that consequence of collapse could increase density by 9 % and more than 10 % the tangential shrinkage. The face of quarter-sawn boards (cut in radial direction) shows a pronounced wavy surface, where the prominent zones correspond to latewood and the recess zones correspond to initial wood (Figure 12-a). The faces of back-sawn boards in general are more regular but the possibility of internal checks is much higher and these checks are oriented in radial direction (Figure 12-b).

(a)

(b)

Figure 12. Consequences of the phenomena of collapse: (a) in quarter-sawn boards; (b) in back-sawn boards.

The presence or the evaluation of the intensity of collapse can be made by observation of surfaces of the boards, by measurement of tangential and radial shrinkage, by calculation of volume changes from green wood to well-defined moisture content or by microscope observation of cell wall shape.

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(a To be sure that we are in the presence of collapse through microscope observation ) revealed much more difficult than expected, perhaps only possible by some very skilled operator. In Figure 13 some examples of collapsed and not collapsed oak wood are presented and small differences could be found. It is much easier to recognize collapse when tangential shrinkage is greater than a certain limit defined for each species. For example a reduction of thickness about 18% is something noticeable but a reduction of 18% in the cell wall thickness is hardly recognized. According to the European Drying Group collapse can be quantified in severe, moderate and low, taking into consideration the difference maximum minus(aminimum thickness in any ( location on the same board.

)

(a ) a

( b

( c

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Figure 13. Pictures of the microstructure of oak, (a) collapsed (magnification 70x); (b) collapsed fibers (magnification 1000x); (c) oak fibers in wood recovered from collapse (magnification 1000x).

2.2.5. Steam Reconditioning Treatment Steam reconditioning treatment consisted in taking the boards from the drying kiln and put them on a thermal insulated compartment where steam is injected inside during different periods, from 2 hours to 6 hours. ( ( This treatment is made in this chamber because steam is very aggressive to metals (corrosion) and usually conventional kilns are not prepared for a so high temperature and humidity. In this box of steam it is not necessary a system of ventilation fans. The boards can be introduced at normal temperature. In the first phase the steam condensates on cold surfaces and water must be drained. Only when steam starts leaving the exhaust tube we count duration of treatment (Santos et al., 1995). The demonstration of the effectiveness of steam treatment can be shown in the tests (Figure 14 and 15). Steam treated wood samples stayed stacked for stabilization of moisture gradient for some days before any test of internal stresses, moisture evaluation or other. The ( on the same board. Before steam reconditioning one comparison studies were done later section of each board were cut along its length and kept outside. Only the remaining part was submitted to steam treatment. This way we could later on make measurements, pictures, etc., putting in comparison exactly the same original material. The back-sawn oak board on (Figure 15) recovered the width and the thickness in a significant amount and also the deformation was almost eliminated.

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(a)

(b)

(c)

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Figure 14. Pictures of prong tests taken from different results after steam reconditioning treatment, for oak. From left to right: (a) succeeded treatment; (b) and (c) presence of internal stresses.

Figure 15. Differences in dimensions and shape for the same kiln dried board of oak. From top to bottom: (a) after steam treatment to recover collapse; (b) before steam treatment.

Prototypes of all types of objects and building components produced with steam reconditioned wood revealed an excellent behavior. Also in the shop work the cutting, planning, profiling was much easier and the qualities of surfaces significantly better. The gluability of the wood and application of finishing had no inconveniences as a result of steam. The treatment increases obviously the price of wood as a result of more operations, energy spending, movements and manpower, but these aspects could not be considered because it depends from the scale of production. But by other hand the alternative of nontreatment can make appear the defects that become the wood almost useless for quality production in solid wood components.

3. WOOD QUALITY AND CLASSIFICATION Wood quality is a relative concept defined by end-use requirements and existing technology. This means that it may be suitable for one purpose but not for another (Carvalho et al., 2009). There are different attributes that can be used to define the wood quality. They

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can be wood intrinsic characteristics and other more related with tree anatomy. Since wood is a biological material its formation is dependent on a wide variety of factors, both internal and external to the tree (Larson, 1969). Different wood uses require different material characteristic specifications (Bartot, 1988). Better wood with less or no abnormalities is used in more demanding applications such as veneer while wood with more features is selected for carpentry and rustic applications. Wood processing technologies may also have an important impact in the optimization of timber use and valuation (Triboulot and Leban, 1998). New processing technologies allow the use and valuation of smaller diameters as well diverse wood applications. Wood quality depends on tree genetics and growing conditions. Different studies showed that physical and mechanical properties vary widely between trees and inside each tree. Wood density has an important influence on lumber behaviour and affects other quality characteristics (strength, durability, shrinkage). For applications of higher value, oak wood with less shrinkage, without cracks, lower proportion of sapwood, pleasant colour and grain are required. It is also important to look for regular growing for technological and aesthetic purposes. Lumber dimensions and small defects for carpentry do not affect so greatly the product quality. Flooring allows the use of different timber dimensions which lets oak wood be profitable. Considering its high natural durability oak wood presents advantages in outside products such as building and garden structures and furniture, without need for chemical preservatives. Because of its resistance to radiation, climatic and biological agents it’s also of great interest in building construction along the coast. Those applications tolerates a large amount of knots and so a valuation of oak wood material. Wood colour and grain are appreciated and their features provide a natural beauty (Mazet and Janin, 1989). Grading rules were developed to segregate wood according to quality requirements in specific uses. Standardized rules ensure that the same grade will represent the same characteristics and value, and can be used for the same purpose. Strength and stiffness of timber are main concerns in the construction industry, pallets and containers. In decorative uses, appearance is the major factor. Different grading rules apply in these situations. The present work relates with grading rules appropriate for non-structural timber. In factory lumber grades defects limit the dimensions (length and width) of clear-face cuttings. Log diameter is important since large logs produce wide boards that can be ripped to eliminate lumber defects. For round wood and sawtimber limits are established for certain characteristics (e.g., spiral grain, crack dimension). Grading of timber may be view too as a marketing strategy ensuring buyers appropriate quality timber for their needs. Material grade is usually determined visually and in some situations a more objective method would be desirable. Some techniques such as optical image analysis can determine wood features offering an improvement in efficiency.

3.1. Roundwood Roundwood classification gives a common utilization and valuation reference for producers and users. Loggers need basic criteria of oak wood timber quality. It answers primary processing industry requirements as well timber quality normalization.

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Round timber classification is useful for a proper log processing. The technological use of wood depends on the size of logs and defects present. Classification considers log size, abnormalities and features. These can be structure and shape irregularities (defects or singularities), degradation and changes in chemical composition of wood. The classification of roundwood uses four grades (A, B, C, D), being assigned a different monetary value for each quality class. A potential use may be assigned for each grade, as indicated in the following Table 2. Log length and minimal diameter are defined for each grade. Round wood classification considers size and qualitative features (Table 2 and 3). These features are structure, shape irregularities and chemical wood alterations. Table 2. Dimensional log characteristics and potential uses for each grade Grade

Potential Use

A

. furniture . furniture . flooring . construction . carpentry . flooring . construction (structure) . construction . beams . palette

B

C

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D

Minimal diameter (cm) 45

Log length (m) 2,5

35-40

2,5

30-35

2,0

25-30

2,0

Table 3. Classification features for oak round timber Dimensional Classification Mean log diameter. Qualitative Classification Structural characteristics colour; sapwood and heartwood proportion; growth ring width. Structural features knots type, number and size; epicormic shoots; bark pocket; burl; gall; buckle; spiral grain; eccentric pith; back pocket; included sapwood. Shape features sweep; ovality; bulge; shake (top, ring, heart, seam, frost, lightning). Deterioration by fungus rot; stain, heart. Deterioration by insects holes; boring. Other degradations carbonized wood; wound; strange objects.

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Quality Classification of Roundwood Dimensional Classification This classification is based on the average diameter of each log, and different diameter classes can be defined. Qualitative Classification

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Structural Characteristics  Color - color and their homogeneity is a feature to consider for some demanding uses. Subjective characteristic of difficult assessment.  Sapwood - section of the log that includes living cells, distinct from the rest of the log and offering low durability. It is expressed by its width.  Heartwood - part of the wood that consists of dead cells, presenting a darker color, resulting from the production and secretion of substances and accumulation of extractive reserves.  Growth ring width - the width of growth rings has an influence on wood quality; for some uses may have an aesthetic impact. Structural Features  Knots - represent a modification of the continuity of fibers affecting the quality and aesthetic value of the wood; also induce deformations in drying; the greater the number and diameter the more problematic. Knots may be visible on the surface of round wood or not (covered knot). It may be sound or unsound; knot diameter and number are measured.  Epicormic shoot - shoot present on the surface of the round timber, marking the existence of a dormant bud.  Rose - concentric ripples of the bark marking a unique internal singularity. Its diameter is measured.  Buckle – round swelling indicating the possible presence of an included knot.  Burl - irregular lump around a group of dormant buds or epicormic shoots.  Spiral grain - results from an abnormal direction of the wood fibers, affecting the mechanical strength of wood and its use suitability; induces deformations in drying. The deviation of the grain in relation to a generating parallel line to the axis of the log is measured.  Eccentric pith - pith away from the geometric center of the cross section of the log; affects the quality of the wood leading to deformations of the products; influences the quality productivity. The distance of the pith to the geometric center is measured, and is expressed as a percentage of the mean diameter.  Back pocket – portion of bark contained in the wood; leads to a loss of quantitative and qualitative productivity; not measurable externally.  Included sapwood - presence of a complete or not growth ring in the heartwood; affects the output of the final product.

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Shape Features  Sweep - deviation of the log straight from the longitudinal axis; leads to a reduction in wood mechanical strength and reduces output productivity.  Burr - local bulge on the log of variable shape and size; influences the quality of the wood, drying performance and productivity.  Ovality - cross section with very different diameters; influences quantitative productivity. The difference between minimum and maximum diameter of the section, as a percentage of maximum diameter, is measured.  Shake - results from the discontinuity of the wood fibers; affects the productivity and provides quantitative degradation of the wood. Shake may be on different places (top, ring, heart) and due to different origins (frost, lightning, harvesting, drying). Deterioration by Fungus  Rot - changes in chemical composition of wood caused by the action of fungi; leads to a degradation of wood.  Stained heartwood - color of the heart caused by the action of fungi; leads to a devaluation of the wood aesthetic.  Rotten sapwood - rotten reaching only the sapwood.

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Deterioration by Insects  Holes - gallery or insect exit hole on the log; the decay caused by insects affect the mechanical strength of the wood; affects qualitative and quantitative productivity as well as aesthetics. Can be classified into small or large holes depending on its diameter is smaller or larger than 3 mm, respectively. Other Degradations  Carbonized wood - the surface of round wood is carbonized by the action of fire or lightning.  Wound healed - superficial wound healed partial or completely; leads to wood degradation.  Strange objects - the presence of strange bodies including wood and non-wood (stone, wire, nails, etc.). A survey study performed in oak forests (Q. pyrenaica) throughout exploitation activities have provided round wood classification. Table 4 presents top diameter and relative proportion for each grade of the timber stock. The following preferential end-use was defined for each grade: A – furniture; B – furniture, flooring, carpentry (window and door manufacture); C – carpentry, flooring; carpentry (structural wood); D – construction (structure); palette. Natural stand characteristics, site quality and management practices have a strong influence on the proportion of each grade. Proper practices are important to obtain a good proportion of the higher grades. The use of wood for either end allow a different monetary value, so it will always be more desirable and profitable production of quality trees, answering the demands of the processing sector and the market.

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Table 4. Oak (Q. pyrenaica) round timber classification. Log top diameter, volume proportion and value for each grade are presented Grade dmin (cm) % (v) €/m3 (road side)

A 40 8,8 350

B 35 23,7 220

C 30 39,4 120

D 25 28,1 60

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3.2. Sawn Timber Classification describes timber quality for industrial use. Surface aesthetics, mechanical behaviour and durability are valuated. Lumber classification is important for a good technological processing and obtaining of uniform lumber and components. The recognition and evaluation of lumber characteristics are done considering its final use. Classification of dried lumber must be realized with objective criteria based on timber abnormalities and singularities and possible defects introduced during the primary processing like drying. Sawing interacts with log form and size and the geometry of boards is defined. A bad drying process can produce defects (fissure, tension, and warp). Drying evaluations and studies for each species and material sizes are important. Hardwood lumber grades are delineated on the basis of the minimum yield of free defect material contained in each board. Classification considers size and qualitative appearance characteristics on the visible face (Table 5). Lower grades admit larger defects. Larger defects are tolerated in larger sized pieces. The best grades are likely to be used with a clear finish while the poorer grades may be painted or concealed. Small knots are preferred to large knots, and intergrown knots are more acceptable. Wane and warp is more controlled while a moderate slope of grain can be tolerated. A board of one species may be quite clear while oak might have considerable decorative figure. The quality classification on sawn boards for other final uses than structural may be found in the European standard concerning sawn timber appearance grading of hardwoods. According to this standard, individual selected boards and boles grading is made on the faces. Only in special cases the grading is made also in edges. The size, position and frequency of features, sawing defects and deteriorations are taken into account. Non-conformity with the conditions applicable to any one of these elements is sufficient to downgrade the piece. Dimensional variation is not taken into account for quality grading and may be covered by other standard or requirements defined contractually. In order to consider variation of pieces dimensions a quality of appearance classification system was developed based on the European standard that considers additional stripe sizes. This allows a valuation of potential boards that presents a higher presence of certain features such as knots which may be obtained from less managed forests. Different dimensions are considered for application and qualification criteria according to the size of the individual boards are used. This principle is also used by the American Hardwood Export Council (AHEC). In the adopted procedure the natural defects were considered for classifying the presence and size of knots, cracks, bends and slope of the edge of the wood. As for the flaws that may

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appear after the drying process, we highlight the warping, cracks, discolorations, and issues related to water content and its distribution in thickness. It was necessary to define the scale of observation to provide an indication of the potential use of industrially usable parts for the manufacture of components. The assignment of the quality class was defined by two directions, the first on the size and quality on the second. Table 5. Classification features for oak sawn timber used to determine quality of appearance

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Size Classification . Length and width. Qualitative Classification . Sapwood: presence. . Knots: number, size, type, adherence. . Fissures: shake type, width, length, depth. . Inclusions: presence of strange elements (bark, carbonized wood, objects). . Pith: presence. . Bark pocket: presence. . Spiral grain: slope of grain. . Deformations: wane, cup, bow, twist, thickness irregularities. . Biological deterioration (insects and fungi): holes, spots, rot, stain. . Spots: colour variations, presence of spots. . Moisture content: final moisture content. . Drying tensions: presence of deformation, compression and tension wood. . Moisture content gradient: moisture content differential between inside and outside.

Size Classification The size classification allows us to consider different lengths and widths of the planks in order to optimize their use. Specifically, lengths of 200 and 80 cm, and widths of 22, 12 and 8 cm. Classifications are obtained by S1 to S6, respectively. Priority is given to the elements longer and for each length to greatest width. Qualitative Classification The criteria used for classification are based on objective parameters. Most of the parameters used for classification are identifiable and quantifiable in sawn wood, but in some cases, the measurement of small knots or small cracks is only possible after the flattening of the faces. The best face is taken for the classification of the boards.  Sapwood - the sapwood of oak is susceptible to insect attack, so their presence represents a risk factor for durability of future timber use. The small presence of sapwood may not pose a significant danger of future attacks and so it can be tolerated.  Knots – only visible knots are considered for classification. Size, adherence and health status are parameters to consider.  Cracks - cracks are discontinuities that affect the mechanical behavior of wood and are indicative of the drying process or tensions, which are decisive for the

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attribution of a quality grading. Surface and internal cracks when visible are considered for classification. Inclusions - presence of any material that is not a constituent of the wood, such as pieces of bark, carbonized wood or strange objects. Any inclusions are not allowed in any of the classes. Pith - area of wood with reduced mechanical strength and very susceptible to warping, shrinkage and more pronounced swells, revealing frequent development of cracks; must be excluded for higher quality requirements. Biological degradation - indication of poor production of timber, improper handling of logs or poor storage. Considers attacks by insects, fungi and bacteria. It is not allowed in any classification level. Curvature and spiral grain - the lack of parallelism between the direction of the grain and the edges of sawed boards is indicative of a curved log or non-parallel sawing to the preferred direction of the fibers, which ultimately compromises the behavior of wood, particularly in structural use. Spots - spots that are not of biological origin may appear as a result of contamination with other substances, or the drying process itself, due to migration of extractives. It allowed a slight variation in color tone uniformly throughout the mass of wood, usually resulting from the artificial drying process. Final water content - the final water content defined for classification, is the value that was determined most appropriate for each of the end uses of wood. When not specified should consider the values indicated in the tables of classification. Drying tensions – portions of dry wood in compression or tension, by the effect of plastic deformation during a misled drying process. These stresses cause deformations when the wood pieces are transformed. Water content gradient - is the existence of different values of water content between the surfaces of the planks and the interior. Results from a misguided drying and cause deformities similar to those listed for the stresses of drying. The verification of gradients can be done by measuring devices in water content with electrical insulated electrodes laterally or weighing the removed layers at different depths.

On a survey performed on oak boards (Q. pyrenaica), a classification was carried out considering two designations, one for size and another for qualitative attributes. The assignment of the final classification was established according to the above criteria (Table 5). A total of 496 boards were obtained and evaluated. Figure 16 shows the classifications results for the different oak boards. Size of the smaller boards (length of 80 cm and width of 8 and 12 cm) are the most representative in the sample. Considering qualitative characteristics, 42% belongs to the better grade (Q1), 35% to the intermediate grade (Q2) and 23% to the lower grade (Q3). Boards without sufficient quality for carpentry and furniture were discarded and represent only 2%. Almost of the boards (98%) were used for manufacture of joinery and furniture parts. The most represented grades were S6Q1 with 13%, S5Q2 with 12% and S5Q1 with 9%. The most common classification in the air-dried planks was S6Q1 with 12.5%, and in artificially dried planks was S4Q1 with 15.2%.

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José A. Santos, João P. F. Carvalho and Joana Santos 50 40

%

30 20 10 0 S1

S2

S3

S4

S5

S6

Size Classes 50 40

%

30 20 10 0 Q1

Q2

Q3

Quality Classes

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Figure 16. Oak sawn timber classification by size and qualitative attributes (Pyrenean oak study). Length and width board size classes, S1: 200 cm, 22 cm; S2: 200 cm, 12 cm; S3: 200 cm, 8 cm; S3: 80 cm, 22 cm; S5: 80 cm, 12 cm; S6: 80 cm, 8 cm. Quality classes (Q1, Q2 and Q3) considers board different attributes (sapwood, knots, cracks, inclusions, pith, biological degradation, spots, curvature and spiral grain, water content drying tensions, water content gradient).

4. END USES OF OAK WOOD Taking into considerations their physical and mechanical properties and yet the great potential in decorative and good durability aspects, oaks have a great potential for use in a great variety of end uses, taking namely as examples, carpentry, flooring and wall coverings, furniture for kitchen furniture, tables, chairs and cabinet doors, outdoor furniture (gardens, terraces), cooperage and many other. It was once widely used in the tanning industry because it has plenty of tannins for chemistry sector. In certain areas the wood of oak species has diminished their use due to the lack of supply in quantity and quality despite good production potential. Lack of proper management and land abandonment has diminished importance of the wood and profit and consequently value and quality losses. The use in energy production should be limited only to the bad quality wood or to the residues of industrial processing, helping to compensate the slightly higher costs of production. Considering its high natural durability oak wood presents advantages in outside products such as building and garden structures and furniture, without need for chemical preservatives.

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In general, oaks and specially the white oaks have a high natural durability against atmospheric and biological agents which is related to the heartwood extractives content but also with the unique anatomic and structural characteristics of the wood. The sapwood is however very vulnerable to insects, especially the Lyctus sp., Anobium sp. and Clytus sp. Table 6 presents the natural durability level of different oak species according to the European standard and Carvalho (1997). Table 6. Natural durability of different oak species Natural durability of the heartwood Agent

White oak Quercus alba Common oak Quercus robur Pyrenean oak Quercus pyrenaica Portuguese oak Quercus faginea Northern-red oak Quercus rubra

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Holm oak Quercus ilex

Decay Fungi 2-3 Durable to moderately durable 2 Durable 1 Highly durable 1 Highly durable 3-4 Mod. to Poorly durable 2 Durable

Insects Anobium, Clytus, Lyctus

Termites

S Susceptible

M Moderately durable

S Susceptible D Durable S Susceptible

M Moderately durable Information not available

S Susceptible

S Susceptible

D Durable

Information not available

Information not available

Note: Decay durability classes: 1 – highly durable; 2 – durable; 3 – moderately durable; 4 – poorly durable; 5 - non durable.

Certain oak species (e.g. Quercus rubra) due to their low natural durability are not suitable for exterior applications. On the contrary, other species (such as Q. robur, Q. pyrenaica and Q. ilex) are widely used for fencing, gates, pallets and mining timber. These uses provide an outlet for lower quality of oak wood than those required for furniture and paneling. The Pyrenean oak presents a very good quality for exterior applications and garden furniture, example in figure xxx, being a relatively easy wood to dry and machining. Parquet flooring and lamparquet of oak are very appreciated and exhibit huge increase in industry, with imported finished products from North America and Europe. Local industries also use species such as Q. rubra, Q. robur, Q. pyrenaica and Q. alba to produce high-quality parquet flooring. White oak allows a good flooring timber, suitable for parquet and solid flooring. Long strip flooring was produced in Pyrenean oak with very good behavior and decorative effect (rustic style flooring). Because of its hardness, holm oak (Q. ilex) is being used for rough work and flooring of heavy industrial wear. Due to the high swelling and shrinkage of oak wood it is necessary to provide the appropriate spacing between strips in order to allow the wood movement along the yearly weather variation.

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The oak wood is known for its beauty and high quality, and that’s why its use in interior furniture is highly valuated. High quality oak timber can be used for paneling and high quality interior joinery and craving and also to produce decorative veneers for furniture. Furniture usually requires good boards. The outer surface demands wood absence of defects while the inner pieces tolerate their occurrence. Recent studies on Pyrenean oak reveled that this specie has a great interest for interior furniture application. Veneer products demand high quality trees which require the right silviculture. Mazet and Janin (1989) showed that surface appearance, colour and presence of small spots are important in aesthetic quality. In general, wood with light colour, fine to medium grain, no important defects, hardiness and mechanical strength not to high is preferred for veneer. Oaks heartwood is very durable so is good for uses in hard conditions like windows or window frames, subjected to moisture and water contact. To ensure dimensional stability a good solution is to produce the frames in glued profiles who contribute to better behavior. Prototypes made on triply gluing gave very good results with different glues, water proof vinilic PVAc and melamine. Cooperage is another important activity for quality wines and brandy. Many wine containers are made of oak, especially for the wine who must be aged for long periods for gaining color and aromatic compounds. For this application only certain species are suitable because of its impermeability to liquids. This is due to presence of tyloses in the interior of the porous. The predominance of tyloses in the pores of white oaks unable the passage of liquids and renders the wood ideal for tight cooperage of wine and other drinking’s. In this group of oaks that combines impermeability and good bending properties, there is the Q. robur, Q. petraea, Q. pyrenaica, Q. alba and Q. ilex. Oak wood is appreciated for storing and aging because of its mechanical properties, permeability, porosity, polyphenolic and aromatic substances content. Wood characteristics for barrel-making vary according to species and origin. Provenance is important and there are some preferences. Sensorial compounds characteristics are important. There are variations between species and locations. Studies show that common oak (Q. robur) tend to have a higher content in tannins and sessile-oak more aromatic; however, there are big individual variations (Guimbertreau, 1987). Pyrenean oak has structural and chemical characteristics ideal for barrel-manufacturing. Recent studies (Cadahía et al., 2007) have also confirmed the good structure and chemical characteristics of Pyrenean oak for wine barrels. Its chemical characteristics (polyphenols, tannins and volatile compounds) are very similar to other oaks for enological use. Pyrenean oak barrels are very high regarded for aging of quality wines. Besides mechanic and chemical characteristics, a sensorial analysis showed its preference compared with other oak woods (Q. alba, Q. petraea). Because of its density, durability and mechanical properties, oaks like Q. robur, Q.alba and Q. faginea were, in the past, greatly employed in many countries for ship construction. Excellence appetencies for this use were also revealed by Pyrenean oak (Q. pyrenaica). The existence of tyloses in the heartwood makes it impenetrable to liquids and ideally suited to the boat industry. Oak wood is also appreciated for firewood due to its high calorific value (5-7000 kcal/kg) and is also used to obtain charcoal. In order to minimize the problems related to inadequate moisture content of wood in different environments, European standards establishes certain guideline values indicated in Table 7. For other uses we can define recommendations presented in Table 8.

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Figure 17. Some high-valuable applications of oak wood (flooring, furniture, cooperage, and garden furniture; detail of a glued profile in a Pyrenean oak window).

Table 7. Recommended moisture content of solid timber by categories related to inservice climates, according to European standards Category External joinery Internal joinery

Sub-category based on intended in-service climates Unheated buildings Buildings with heating providing room temperatures of 12-21oC Buildings with heating providing room temperatures in excess of 21oC

Moisture content 12-19 % 12-16 % 9-13 % 6-10 %

Table 8. Recommended moisture content of solid timber in exterior conditions Type

Description

Moisture content

Green

Freshly sawn

Not specified

Air dried

Dried outside

20-25%

Usage Suitable for use outdoors when changes in size are not a problem, e.g. fencing, cladding, decking, garden furniture; ship construction. Suitable for use with outdoor construction.

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Jointing and Gluing The jointing between the various components obtained in the phase of operation can be done in different shapes and different materials. The success of the various bonding processes depends on the physical and mechanical properties of each wood species. Oak wood has a good ability to glue (PVA glue, resorcinol formaldehyde, epoxy) and fixation with metal bodies.

Surface Finishing Corresponds to the terminal phase of all the actions that relate to technological change and to improve the aesthetic appearance of the visible part, increasing resistance to normal weathering phenomena or erosion, and reduce hygroscopicity. Various products can be used for this purpose that can have multiple properties (insulation, sealing, protection). With regard to surface finishes, it can be stated that while preparing the surface is delicate, oak wood is relatively easy to impregnate with varnishes and waxes. The open pores absorb more stain, so the grain pattern becomes quite evident when a dark stain is applied. Under heavy exposure conditions, for example the UV radiation and rain, is recommended the annual maintenance of the finishing. The delamination can be a problem with the film forming finishes. If it is not possible to establish a frequent maintenance program it should be better to opt for finishes with oils and UV pigments. Maintenance can be sparser but mainly it is simplest and cheaper.

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ACKNOWLEDGMENTS This work was partially funded by the following R&D projects: European research project AIR2-EC ‘Improvement of Mediterranean Oak Forests’ (1994-98); ‘Quality of Oak Forests and Technological Improvement’ supported by the Foundation for Science and Technology (1997-2000); ‘Valuation of Oak Forests’ by the National Institute of Agrarian Sciences, Portugal (2002-04).

REFERENCES Barreal, J.A.R. (1988). Improvement in Dimensional Stability Against Water of the Main Spanish Timbers Impregnated with Water Repellent Organic Protectors. Madrid, 17 pp. Bartot, Ch. (1988). Bois de qualité et qualité des bois. Revue Forestière Française, XL, 423431. Cadahía, E., Fernández de Simón, B., Vallejo, R.; Sanz, M. & Broto, M. (2007). Volatile compounds evolution in Spanish oak wood (Quercus petraea and Quercus pyrenaica) during natural seasoning. Am. J. Enol. Vitic. 58(2), 163-172. Carvalho, A. (1997). Madeiras Portuguesas. Instituto Florestal, Lisboa. Carvalho, J.P.F. (2005). O Carvalho Negral. Ed. João P. Carvalho; UTAD – Sersilito; Maia.

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Carvalho, J.; Santos, A.; Reimão, D.; Rodrigues, A.; Borges, A.; Alves, E. & Duro, M. (2004). Potencialidades da madeira de carvalho-negral para a indústria da construção. In: A Madeira na Construção, Proc CIMAD04 1º Congresso Ibérico, Guimaraes, 133140. Carvalho, J., Santos, J. & Santos, J. Quality Control and Productivity of Oak Timber - From Forest to the Primary Processing. In: Quality Control for Wood and Wood Products, Proc Cost Action E53 Conference 22–23 Oct, Lisbon, 2009, 3- 19. Choong, E.T. & Barnes, H.M. (1969). Effect of Several Wood Factors on Dimensional Stabilization of Southern Pines, Forest Products Journal, 19 (6), 55-60. Cividini, R. (2001). Conventional kiln-drying of lumber compendium. NARDI; Timber Drying Kilns; Verona. Duarte, M. C. (1992). Técnicas de Estabilização Dimensional da Madeira. Instituto Nacional da Engenharia e Tecnologia Industrial; UTMC; Lisbon; 62 pp. Farmer, B.A. (1981). Handbook of Hardwoods. 2nd Edition; Department of the Environment; Princes Risborough Laboratory; London. Forest Products Laboratory (1999). Wood handbook—Wood as an Engineering Material. Gen. Tech. Rep. FPL–GTR–113; Forest Service; USDA; Madison WI. Guiembertreau, G. (1987). Le bois et la qualité des vins et des eaux-de-vie. Connaissance de la Vigne et du Vin. Innes, T. C. (1995). Collapse free pre-drying of Eucalyptus regnans F. Muell. Holz als Roh und Werstoff 53, 403-406. Kollmann, F.; Kuenzi, E. & Stamm, A. Principles of Wood Science and Technology. In: Wood Based Materials. Springer-Verlag; Berlin; 1975; 116-139. Larson, P. (1969). Wood formation and the concept of wood quality. Yale Univ.; Bulletin 74. Mazet, J.-F. & Janin, G. (1989). Recherche des critères pour l’aspect (dessin et couleur) des placages de bois de Chêne. Cahiers Analyse Données, 14, 365-376. McMinn, J. W. & Stubbs, J. (1985). In-woods drying of eucalypts in southern Florida. Forest Products Journal, 35 (12/13), 65-67. Nepveu, G. (1984). Déterminisme génotypique de la structure anatomique du bois chez Quercus robur. Silvae Genetica 33, 91-95. Nepveu, G. (1991). La variabilité du bois. In: Le materiau bois ; Arbolor; Nancy. Neumann, R. J. & Saavedra, A. (1992). Check formation during the drying of Eucalyptus globulus. Holz als Roh und Werstoff 50, 106-110. Perré, P. et al. (2007). Fundamentals of Wood Drying. Ed. Patrick Perré. European COST; ARBOLOR; Nancy. Polge, H. (1973). Facteurs écologiques et qualité du bois. Ann. Sci. For. 30, 307-328. Santos, J.; Reimão, D.; Carvalho, J. & Santos, J.. Madeira. In: O Carvalho Negral. Ed. J. Carvalho, UTAD-Sersilito, Maia; 2005; 87-114. Santos, J.A.; Reimão, D. & Borrego, F. (1995). Dimensional Stability of Portuguese Wood Species. COST Action E-2 Workshop; Ljubljana; 10pp. Siau, J.F. & Meyer, J.A. (1966). Comparison of the Properties of Heat and Radiation Cured Wood - Polymer Combinations. Forest Products Journal, 16, 47-56. Triboulot, P. & Leban, J.-M. (1998). Le bois – Nouvelles technologies et nouveaux matériaux. Fôret Enterprise, 119, 17-22. Wilson, K. & White, D.J.B. (1986). The Anatomy of Wood: its Diversity and Variability. Stobart and Son, London.

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Zobel, B.J. & van Buijtenen, J.P (1989). Wood Variation – Its Causes and Control. SpringerVerlag, Berlin.

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Chapter 5

DIVERSIFICATION OF CORK OAK STANDS TRADITIONAL PRODUCTION MANAGEMENT: A REVIEW Sofia Knapic Forest Studies Centre, College of Agronomy, Technical University of Lisbon, Lisbon, Portugal

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ABSTRACT The objective of this work is a review on the diversification of cork oak (Quercus suber L.) stands, aiming at the mixed production of cork (always the main product) and wood (from thinning operations). This can be done without competing with the cork production, with the wood providing an extra market value and opportunities. The trees were obtained in the South-western Portugal (cork production region of Alentejo). The trees were felled under an authorization due to public construction since there are strict and legally enforced regulations on cork oak felling. Oaks are considered to be a valuable source of timber for construction purposes and they are highly regarded for indoor joinery and furniture due to good mechanical properties and aesthetical value. One of the potential uses of cork oak wood is for flooring products that take advantage of the high density values (0,86 gcm-3 to 0,98 gcm3 ), strength and wear and friction resistance of the wood, as well as of the pleasant macroscopic structure and color. To evaluate the most adequate flooring components to produce 3D modeling and simulation techniques were used regarding the industrial transformation. The maximization of the production yields was achieved with small logs and short dimensions components (parquet and components for multilayer composites). Further, relevant properties for flooring applications (hardness, wear and dimensional stability) were assessed.

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Sofia Knapic Conclusions show the technological feasibility of cork oak wood to flooring applications (with high traffic uses), and therefore a strong alternative to other oak and tropical species.

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INTRODUCTION The cork oak (Quercus suber L.) occupies large areas around the western Mediterranean basin in Southern Europe and North Africa, over a total area of about 2 million ha, mainly in Portugal and Spain. In Portugal the cork oak stands are mainly located in the south showing a successful adaptation to Mediterranean climatic types to high summer temperatures and drought (Natividade 1950; Pereira and Tomé 2004). Cork oak is a very important specie in Portugal’s forestry and socio-economy has it is the responsible for the production of cork. Portugal is the world’s major cork producer and transformer with about 51% of the world production (Fortes et al. 2004). Most of the cork oak forests integrate an agro-forest system that combines forest, agriculture and animal production, called “montado” in Portugal and “dehesa” in Spain. The cork oak forests play an important ecological role due to their adaptation to poor soils and harsh climatic conditions of summer droughts and high temperatures while allowing a considerable biodiversity in the ecosystem (Pereira and Tomé 2004). The cork oak is an evergreen oak that is characterized by the presence of a thick bark with a continuous layer of cork in its outer part. It is this cork, is the raw-material used as sealant for wine bottles, bark that gave the cork oak its notoriety and economic importance as a cork producer, as well as its ornamental value (Pereira 2007). Portugal has a total of 3412.3 thousand ha of forest according with the last data of the National Forest Inventory (AFN 2010), with the cork oak forests representing 716 thousand ha. During the Discoveries period (16th century) cork oak wood was one of the most valuable woods for carpentry, cabinet making and ship building due to its high resistance to compression and impact, as well as durability. In this last century, the cork oak stands have been almost exclusively oriented towards the production of cork. It is therefore not strange that research has concentrated on cork (Fortes et al. 2004) and cork production related issues, i.e. production modeling (Falcão and Borges 2005; Silva and Louzada 2001; Vasquez and Pereira 2005; Williams et al. 2001), and little has been done on cork oak wood characterization. However it is important to have options for diversifying cork oak exploitation, thus circumventing the danger of a cork-only production and of the resulting economic dependence on the wine stopper market. This is especially relevant now that the wine industry is increasingly using substitute closures. In this context the potential of cork oaks for production of high value wood products should be considered. This diversification targets a mixed production of cork (always the main product) and wood (from thinning operations), without competing with the cork production, with the wood providing an extra market value and opportunities. Also the availability of considerable amounts of cork oak wood is foreseen resulting from thinning material from recently planted areas, corresponding to approximately 140 000 m3 in 2059. This rationale led to a series of research projects (national and international) and two doctoral thesis, in order to develop research on the technological quality of cork oak wood, namely on important properties such as density, or stem quality for sawing and production of

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wood products, to be used either as solid wood or in composite or assembled products such as flooring components. All this projects were coordinated by Centre of Forest Studies, College of Agronomy, Technical University of Lisbon, that has been pioneer on this subject. In order to evaluate the potential of the diversification of cork oak stands traditional production management it was necessary to study this wood towards its density, productions yields for sawn pieces and behavior in use. The cork oak trees used for this study were felled in the cork production region of Alentejo in South-western Portugal, in low-density stands typical of the montado agro-forestry system. The trees were available for study from legal fellings due to road construction since there is a legal ban to harvest cork oaks. The trees presented good vitality and phytosanitary conditions.

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CORK OAK WOOD DENSITY VARIATION Oaks are valuable timber species and oak wood is highly regarded for indoor joinery and furniture due to its mechanical properties and aesthetical value. Size and absence of defects such as knots or grain direction are also important aspects for acceptance of oak timber for higher value products. Wood density is one of the most important properties since it correlates to other physical properties, namely mechanical strength and performance in use. Oak wood density has been studied extensively, i.e. for Quercus robur and Q. petraea in France (Ackermann 1995; Bergès et al. 2000; Degron and Nepveu 1996; Guilley et al. 1999). Most of the studies dealing with the within-tree and between-tree variation of wood density have used X-ray microdensitometric techniques as developed by Polge (1965, 1978). Cork oak trees were study to obtain X-ray microdensitometric data to evaluate the variation with age of ring width and of the density components for two groups of trees: young and never debarked trees, and mature trees under cork production with a 9-year extraction cycle (Knapic et al. 2007). Cork oak trees were divided into two groups, mature cork oaks under full production of cork with a 9 year cycle (with a stem wood diameter at 1.3 m ranging 39 cm to 43 cm) and younger trees from which cork was never removed (with a stem wood diameter at 1.3 m ranging 27 cm to 34 cm). The date of the first cork removal was not recorded but it is estimated as having occurred at about 25 years of age, the last cork removal was in 1996. From each tree a 4 cm-thick disk was taken at breast height (1.3 m), and was sawn into a 2 mm-thick radial strip segment from the pith to the bark. The strips were conditioned at 12% moisture content. These radial samples were X-rayed perpendicularly to the transverse section and their image scanned by microdensitometric analysis as described by Polge (1965, 1978). The time of exposure to radiation was 350 s, at an intensity of 18 mA and an accelerating tension of 12 kV, with a 2.5 m distance between X-ray source and film. The data composing the radial density profiles were recorded every 100 µm with a slit height (tangential direction) of 455 µm. The choice of a 100 µm radial windows was due to the fact that the species is a hardwood, with large vessels with average diameters over 100 µm and attaining in large vessels values over 200 µm (Leal et al. 2006). A smaller size for the radial windows would

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lead to higher amplitude of the variation of density within the rings and, therefore, to a higher number of density peaks within the ring, which would make it more difficult to identify the rings. Average ring density (RD), minimum density (MND), maximum density (MXD), earlywood density (EWD), latewood density (LWD), ring width (RW) and latewood percentage (LWP) were determined for each ring. The growth ring boundaries were identified on the radial profiles by locating the sharp density variations with a cross-examination using a visual observation of the macroscopic anatomical features namely the vessel distribution. The earlywood and latewood in each growth ring were calculated using the average of the minimum and maximum density values within each ring for their distinction, i.e. the latewood was calculated from all the points with a density higher than this average value (Degron and Nepveu 1996; Mothe et al. 1998; Sanchez-Gonzalez et al. 2005). Therefore, this criterion does not allow an identification of the beginning of the latewood, but only the portions of the ring with a density higher than a certain threshold, which we call here latewood. The intraring density variation was quantified by the heterogeneity index (HI) proposed by Ferrand (1982), defined by the standard deviation of all density values across the annual ring. Analyses of variance for all density components were performed according to the model presented in Table 1 to test the significance of tree group (never debarked, and under cork production), trees and rings (age) effects. Variance components for the sources of variation were also estimated. The cork oak has a semi-diffuse porosity with large vessels formed in the beginning of the growing season that gradually decrease to the end of the ring. This pattern is usually well defined in young cork oaks before about 20 years of cambial age (ring number from the pith) but become later on more confused especially in the case of older cork oaks under cork production (Gourlay and Pereira 1998). Figure 1 shows a radial density profile for a never debarked tree and an already debarked tree. Ring distinction may not be obvious as exemplified by the density profile of Figure 1b. A visual cross-examination with the wood strip was therefore necessary to clear out uncertainties. This process was certainly tedious and required a trained eye for observation of cork oak wood anatomical features. Table 1. Model for analysis of variance for the density components of cork oak trees Sources of Variation (1) Groups

Degrees of Freedom s-1

Error Term

Expected Mean Squares 2 2 2 + r T/S + tr S

(2) Trees/ Groups

(t-1) s

2

+r

(3) Rings

r-1

2

+ ts

(4) Rings x Groups

(r-1) (s-1)

2

+t

(5) Residual (R x T/S)

(r-1) (t-1) s

2

2

T/S

2R 2

RS

s = number of groups (2); r = number of rings (30); t = number of trees/groups (estimated in 3.43 according to the formula proposed by Sokal and Rohlf [26], p. 214). 2 2 2 2 2 , are variance components due to groups, trees/groups, rings, rings x S T/S, R, RS, and groups interaction and residual (or error), respectively.

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(a)

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(b)

Figure 1. Radial density profiles for a never debarked tree (a) and an already debarked tree (b).

In spite of this difficulties the density profiles obtained showed that there was a trend for the decrease in density in the transition from the latewood of one ring to the earlywood of the next year that could be used to mark ring boundaries. The mean annual growth was 3.9 mm yr-1 ranging in individual trees from 2.1 mm yr-1 to 5.3 mm yr-1. The cork oak wood revealed a very high mean density that ranged between 0.75 g cm-3 and 0.95 g cm-3, with an average earlywood density of 0.80 g cm-3 and latewood density of 0.90 g cm-3. The latewood corresponded on average to 57% of the annual growth. The proportion of latewood growth in the ring varied between 54.6% and 61.1% between years and did not present an age-related variation trend. There was no relation between annual growth and proportion of latewood growth, as it is shown in Figure 2. Regarding the variation of ring mean density with age, there was an average decrease of density in the first 20-30 years with a subsequent stabilization but overall the radial variation of mean density was small. There was no relation between ring width and mean ring density, as shown in Figure 3. Within the ring the heterogeneity index was very low with an average of 0.05 and without variation with ring number. The density difference between earlywood and latewood was small and constant (on average 0.10 g cm-3). Similar values were reported for the very homogeneous poplar wood (Sokal and Rohlf 1981) and below the mean 0.13

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reported for Pinus pinaster wood (Louzada and Fonseca 2002), also considered a homogeneous softwood (Aubert 1984).

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Figure 2. Variation of latewood proportion with ring width.

Figure 3. Variation of mean ring density with ring width.

Table 2 provides the descriptive statistics for ring width and density components for the two types of cork oak trees (under cork production and never debarked cork oaks) for the first 30 rings. Table 3 shows a summary of the variance analysis for each wood density component and ring width, with their significance and the percentage of total variation due to each source of variation. There were no significant differences between the two groups of trees for all the variables. In the majority of the cases the between-tree variation was very highly significant and accounted for most of the total variation. The age effect given by the between-ring variation was highly significant to explain the variation in the density component variables but contributed less to the total variation, e.g. 45.6% and 12.7% of the total mean density variation respectively for the tree and age effects.

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Table 2. Descriptive statistics for ring width and density components for the two types of cork oak trees (under cork production and never debarked cork oaks) for the first 30 rings Trait

Global Mean 0.894 0.792 0.974 0.835 0.933 0.052 4.17 57.81

RD MND MXD EWD LWD HI RW (mm) LWP (%)

Never debarked trees Mean Min. Max. 0.901 0.832 0.947 0.797 0.724 0.848 0.984 0.919 1.030 0.841 0.773 0.890 0.942 0.873 0.990 0.054 0.052 0.055 4.59 4.35 4.80 57.07 56.40 58.13

CV (%) 6.74 8.13 5.90 7.23 6.54 2.30 4.94 1.62

Under cork production trees Mean Min. Max. CV (%) 0.886 0.730 1.025 12.07 0.787 0.647 0.929 14.64 0.964 0.810 1.091 12.01 0.828 0.683 0.965 13.94 0.923 0.775 1.056 12.47 0.051 0.048 0.056 7.43 3.75 2.18 5.75 40.36 58.54 52.17 62.55 8.14

RD, average ring density; MND, minimum density; MXD, maximum density; EWD, earlywood density, LWD, latewood density; RW, ring width; LWP, latewood percentage; HI, heterogeneity index.

Table 3. Summary of the variance analysis for each wood density component and ring width, showing their significance and the percentage of total variation due to each source of variation

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Sources of variation Tree Group Tree/Group Ring Ringxgroup Residual

RD Sig. % ns 0.0 *** 45.6 *** 12.7 * 6.8 34.9

MND Sig. % ns 0.0 *** 39.4 ** 6.6 ns 5.1 48.9

MXD Sig. % ns 0.0 *** 43.4 *** 15.6 * 5.9 35.1

EWD Sig. % ns 0.0 *** 41.1 *** 8.3 ns 5.9 44.6

LWD Sig. % ns 0.0 *** 44.1 *** 13.7 * 7.5 34.8

HI Sig. % ns 0.2 ns 0.0 ns 7.3 ns 0.0 92.5

RW Sig. % ns 0.0 *** 22.8 ns 2.9 ns 0.0 74.3

LWP Sig. % ns 0.0 ns 3.6 ns 0.05 ns 1.8 94.6

RD, average ring density; MND, minimum density; MXD, maximum density; EWD, earlywood density, LWD, latewood density; RW, ring width; LWP, latewood percentage; HI, heterogeneity index.

The variability was slightly higher in the group of trees under cork production (even if between group variance was equal), as reflected by the higher coefficients of variation of the means (Table 2). The heterogeneity index had only a small variability and it was not influenced by the studied factors (Tables 2 and 3). In relation to ring width the tree effect was very highly significant and accounted for 22.8% of the total variation. The between-tree differences were higher in the group of mature trees in cork production where the average tree ring width ranged between 2.2 mm and 5.8 mm, while in the trees before cork extraction it ranged between 4.4 mm and 4.8 mm. The latewood component in the ring width remained particularly constant and was not significantly influenced by any of the studied sources of variation. Overal the cork oak trees had an average density of 0.86 g.cm-3 with mean tree values ranging from 0.75 g.cm-3 to 0.95 g.cm-3, hence a very dense wood compared to other hardwoods. The values are identical to some tropical species such as Apidosperma, Bowdichia, Chlorofora, and Dalbergia (Fearnside 1997; Hidayat and Simpson 1994; Pereira and Tomé 2004; Zhang 1997). In relation to other Quercus it shows average values identical

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to Q. pendunlata (0.82 g.cm-3), Q. cerris (0.85 g.cm-3) and Q. ilex (0.96 g.cm-3), or higher than Q. petraea (0.51-0.85 g.cm-3), Q. robur (0.50-0.66 g.cm-3) and Q. liaotungensis (0.66 g.cm-3) (Bonamini 1996; Degron and Nepveu 1996; Deret-Varcin 1983 ; Zhang et al. 1993; Zhang and Zhong 1991; Zobel and van Buijtenen 1989). The never debarked trees showed a decrease of the density components with age in the first 30 rings, whereas the trees that had been already debarked presented a much smoother reduction of density. It is common to observe an accumulation of extractives in the first rings corresponding to the heartwood, which contributes for the high values of density in that region. Since this was not the case regarding the already debarked trees it can be speculated that after the debarking there is a tree response to prevent wood degradation favoring the scar formation with a displacement of extractives from heartwood to the outer sapwood, thereby reducing wood density in the innermost rings and increasing it in the outward rings. Therefore in trees under cork production there will be an outwards directed radial shift of extractives leading to a relative stabilization of density along the radius in these trees. It could also be observed that it was in the group of the trees under cork production that the between-tree variation of the density components was higher. This may result from a difference in the individual tree response capacity to the cork extraction trauma. However the response of the cork oak to the removal of cork and the factors that influence it are still a matter requiring further research. Regarding wood growth the value reached 3.9 mm (4.2 mm in the first 30 years), which is considered to be a high value compared with other Quercus (e.g. 1.53 mm and 1.90 mm reported for Q. petraea and Q. robur) (Degron and Nepveu 1996 ; Zhang et al. 1993). Very little information is available for Q. suber but ring widths of 2 mm.yr-1 for young trees (Nunes 1996) and values ranging from 1 mm to 4 mm.yr-1 in mature cork oaks (GonzálezAdrados and Gourlay 1998; Gourlay and Pereira 1998) have been reported. Indirect calculations have estimated an average radial wood increment of 1.3 mm.yr-1 in one 8-year period following a cork extraction in mature cork oaks in full cork exploitation (Costa et al. 2002). The high density and density homogeneity of cork oak wood confirm its value for use in some solid wood applications and the opportunity to consider the wood component in the silviculture and long term management of cork oak stands. Additionally to the high density, the substantial annual growth rates of Q. suber also advise to consider its role for biomass production and carbon storage, especially taking into account its natural growth environment.

MODELING AND SAWING SIMULATION TECHNIQUES APPLIED TO CORK OAK WOOD Yield and sawing efficiency are key factors for the optimization of the whole wood conversion chain and for its economic outputs. In this context, modeling and computer simulations allow to study the impact of raw-material and process variables on conversion. Wood sawing simulators have been designed and improved in order to build an accurate virtual wood conversion chain linking raw material properties to industrial production and products (Hallock et al. 1978, Leban and Duchanois 1990, Schmoldt et al. 1996, Todoroki 1996, Usenius 1999). The impact on sawing yields of specific conversion variables and

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scenarios may be analysed using the virtual sawing of logs and trees (Richards 1973, Todoroki 1994, Maness and Lin 1995, Pinto et al. 2002, Ikonen et al. 2003). Tree modelling and reconstruction algorithms including tree shape and internal structure, i.e. knots and heartwood, provide the input information for process simulation and optimisation (Oja 1997, Björklund 1999, Pinto et al. 2003, 2004). The use of virtual tools in the planning phase of wood conversion is especially important for cork oaks, since availability of trees for direct experimentation is limited due to the existing legal constraints on cork oak harvest (Knapic et al. 2011). With the production of sawn pieces for flooring components in mind, it was imperative to assess how maximize yields. To do so it was necessary to develop 3D-stem models and apply them to computer sawing simulation programs in order to investigate different scenarios for the production of potential solid cork oak wood products. The WoodCIM® software from VTT - Technical Research Centre of Finland was used for stem reconstruction and sawing simulation (Usenius 1999, 2000). The stems (divided in two groups as they had been already debarked or not) were cross cut into 20 mm flitch/slab with the live sawing method. Prior to sawing, a reference line was drawn orthogonal to the saw blade on the stem butt and top cross sections. Each flitch/slab was marked with a code allowing the identification of its position in the stem. The flitch/slab were scanned using the WoodCIM® camera system providing RGB colour component information and the scanned images were processed using the PuuPilot image analysis software from VTT. On the flitch image and with assistance from the operator, the system registered the xy-coordinates of the geometrical outline of the bark, inner-bark, wood and heartwood (when present) as well as of the log pith line. Defects were also registered, classified as knots (with respective quality), discoloration areas, debarking wounds and insect wounds. The mathematical reconstruction of the log in the xyz-coordinate system was based on the geometrical features of the flitch and its thickness, with the support of the reference line to create the third coordinate. Mathematical reconstruction algorithms were used to produce 3D virtual models of the cork oak stems (Song 1987, 1998; Usenius 1999). These provided the data for studying the stem quality and were used as virtual raw material for the sawing simulations. Cross-sections of the stem were described with a set of 24 radial vectors between the pith and the outline points of the surface of the log in 50 mm intervals along the length of the log. Figure 1 represents the three-dimensional reconstruction of a mature cork oak stem. Heartwood could be out singled in the mature cork oaks, therefore allowing the reconstruction of heartwood development within the stem. Figure 2 displays an image of a board of a mature tree (a) and a detailed image with the identification of the knots present (b). No attempt was made to model the knot architecture of cork oak stems since knots, as other defects, were spread rather randomly within the stem (Figure 3). This stresses the importance in virtual representations of using algorithms adapted to the species. Stem and log shape was described by mean diameters at butt and top ends, by taper and pith curviness. These were calculated using the geometric co-ordinates from the reconstructed logs/stems. Taper is the slope of the line obtained from a mean radius calculated for each 50mm along all length. The radius is the average of all vectors that define each cross-section. Log reconstructed diameters were calculated as the double value of the average radius (Pinto et al. 2005). Pith curviness is defined as the maximum deviation (in any direction) of pith,

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found along the log, in relation to an imaginary axis defined by a straight line connecting the pith points at butt and top end of the log (mm) (Pinto et al. 2005).

Source: VTT.

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Figure 1. Three-dimensional reconstruction of a mature cork oak stem (heartwood in black).

Source: VTT. Figure 2. (a) board of a mature tree; (b) detailed image with the identification of the knots (in blue).

Regarding taper results there was a significant variation between stems, from an almost cylindrical to a more conical form (taper of 1 and 45 mm/m respectively). The mean value of 24 mm/m lies in the range of stem tapers considered adequate by the sawing industry. The conical form is more accentuated in the lower part of the stem, in the first half meter above ground (70 mm/m) and remains after that substantially constant at an average value of 22 mm/m. The curviness also varies between the individual cork oaks, from straight to significantly crooked stems (curviness of 11 to 104 mm respectively) with a mean value at 40 mm. The curviness is higher when considering the full stem than in 0.5 m sections, as should be expected. The curviness is somewhat higher in the lower and in the upper part of the stem (15 and 10 mm respectively) than in the mid part (7 mm).

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Bucking into logs increases the mean taper and decreases the curviness. Young cork oak stems show on average lower taper and higher curviness than mature cork oaks.

Source: VTT.

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Figure 3. Boards sequence where it possible to see the randomness of knot distribution (black circles).

With the 3D models already developed WoodCIM® software modules for bucking and sawing simulation were used. The bucking module allows cutting the virtual stems into any log length and the sawing simulation model uses different sawing set-ups for each log and selected the best combination of sawing patterns and dimensions of the sawn products to maximize the product yield. The log lengths chosen were 500 mm and 1000 mm, and of course the whole stem, and the tested sawn products were components for flooring (current commercial products) of varying thickness, width and lengths, planks, parquet, lamparquet, and external component of multilayer planks. Planks were only produced from full stems since the tested bucking lengths were not compatible with the length dimensions of floor planks. The nominal and green dimensions of the products saw kerfs and prices of the sawn products and by-products were introduced as input variables. The simulation program calculated the sawing yield using this input variables for each log and then selected the best combination of sawing patterns and dimensions of the sawn products to maximize production yields. This process did not take into account the inner defects hence they could not be modeled due to their random nature of appearance. Therefore differences in product value are based on differences of volume yield considering the number and dimensions of the sawn components. Simulation outputs were given for the entire batch of logs, for the logs of one stem, and for the individual logs in volume percent of products in relation input raw-material. Yields ranged from the lowest value of 21% (planks from young trees) to the highest value of 54% (multilayer components from 1 m logs from mature trees). Higher yields were obtained for mature trees when compared with young trees. Batch yields ranging from 38 to 43% and from 39 to 50% were obtained from 0.5 m logs, for young and mature trees, respectively, while for 1 m logs, batch yields ranged 34 to 41% and 46 to 54%. Regarding the use of the whole stem, batch yields were lower, ranging 21 to 38% and 33 to 50%.

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The stem yields obtained with 1 m bucking are very similar although slightly higher than when using the full stems (due to stem configuration, i.e. high curvature). For 0.5 m logs, the differences are larger with stem yields decreasing for the larger stems and increasing for the smaller stems, therefore making yields rather constant across stem diameters. As regards products, the best choices to achieve maximization of yields for all log lengths were parquet and multilayer components, and lamparquet for the smaller diameter logs. Planks were obtained in acceptable yields only for stem with a minimum diameter of 250 mm.

PROPERTIES OF CORK OAK WOOD RELATED TO SOLID WOOD FLOORING PERFORMANCE Cork oak wood was assessed to evaluate its potential performance as solid wood flooring. Standard tests on dimensional stability, wear, swelling and hardness were performed according to the European standards (Knapic et al. 2011).

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Dimensional Stability The tests were conducted under the European standard EN 1910. The samples were placed in a controlled air temperature and relative humidity room (Fitoclima “Walk-in 8000EDTU”) that assured a temperature precision of ± 2 ºC and a relative humidity precision of ± 5 %. The samples were subjected initially to a two week stabilization period, at 20 ± 2 ºC and 65% ± 5 % air relative humidity, followed by a four week exposure period with two stability conditions: 20 ± 2 ºC and 85% ± 5 % relative humidity; and 20 ± 2 ºC and 30% ± 5 % relative humidity. Throughout the process the samples were weighted (Scale Pionner PA4102C, capacity 4100 g, precision 0.01 g) to evaluate water content and measured in the radial direction using a warp reading system composed by three digital Mitutoyo measurers with 0.01 mm precision, to establish the warp (cup) formation. For each condition of stability the cup was measured at the middle of the width of the test specimen. The cup was taken as the percentage of the distance separating the face of the specimen from the reference line joining the edges of the specimen over its width (Figure 4). The wood equilibrium moisture content determined under the dimensional stability test conditions was 7.7 - 8.2, 10.4 - 12.1 and 13.3 - 16.8% respectively at 30 %, 65 % and 85 % relative humidity. Warp, measured as the cup (deviation from a flat plane from side to side), was between 0.1% - 0.3%. Cork oak wood showed cup values below the 0.5 % threshold limit mentioned in the European standard EN 13226 related with solid parquet elements. Recent studies (Sousa et al. 2008) showed that cork oak wood presents an average tangential swelling coefficient of 0.306 %, an average radial swelling coefficient of 0.137 % and an average fiber saturation point of 28.4 %.

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The movement of cork oak wood was therefore estimated as 3.99 % considering a 9 % change of moisture content (from 11 % to 20 %) (Ross 2010). This value allows classification of cork oak wood as showing a medium movement in service. Similar results were found for other oak species (Anon 1976) such as american red oak (Quercus rubra) and european oak (Quercus robur).

Figure 4. Warp reading system composed by three digital Mitutoyo measurers with 0.01 mm precision (left); cup determination (right).

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Swelling When Exposed to Liquid Water The test was adopted from the procedure described in annex G of the European standard EN 13329. Wood flooring generally shows a poor behavior when exposed to liquid water e.g. in the course of an accidental water leakage. This test allows evaluating the performance of a floor element in such situations. Two types of pieces were cut from each board, according to the largest dimension along the length of the board e.g. axial direction (L specimens) and according with the major dimension transversal to the length of the board e.g. tangential direction (T specimens). The samples were stabilized in a controlled atmosphere at 23 ± 2 ºC and 50 ± 5 % of relative humidity. The test was completed when mass loss was lower than 0.1% in two consecutive weights in a 24 hour period. After stabilizing the test pieces were weighted (Scale Pionner PA4102C, capacity 4100 g, precision 0.01 g) and measured in two points (Figure 5). The measurements were made using a Mitutoyo reading table with a digital comparator Mitutoyo with 0.01 mm precision. In the L specimens both measurements were made perpendicular to the direction of wood fibers (giving an assessment of the board transversal swelling). In the T specimens one of the measurements was made perpendicular and the other parallel to the direction of wood fibers (giving an assessment of the board transversal and longitudinal swelling, respectively). The test pieces were partially immersed (50 mm) in a recipient with water at 20 ± 1 ºC and after a period of 24 hours taken out, weighed and measured at the measuring points (Figure 5) to determine variation of dimensions. As regards swelling with liquid water there is no axial variation, usually corresponding to the length of flooring boards, and the values regarding radial and tangential variation are low when compared e.g. with Populus tremuloides (Cai et al. 2007).

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Figure 5. Test pieces with measuring points indicated by arrows.

The swelling values show that an accidental water leakage leads to a performance of cork wood flooring boards well above the one expected from laminated floor for which a swelling inferior or equal to 18 % is required by EN 13329 or wood veneer floor coverings for which swelling is required to be inferior or equal to 10 % by EN 14354. Short-term thickness swelling is an important factor while analyzing the performance of wood-plastic composites, which is a current alternative flooring material to solid wood. A recent study presents for six different wood-plastic boards a 24 hour swelling between 2.10 % and 3.63 % (Kamdem et al. 2004). This range of values is similar to the results obtained for cork oak wood. Cork oak wood can therefore be considered to present a satisfactory behavior when subject to shortterm exposure to liquid water.

Hardness The tests were conducted in a controlled atmosphere at 20 ºC ± 2 ºC and 65 % ± 5 % relative humidity, using a universal machine AG 250KNIS-MO from Shimadzu, capable of measuring the load with an accuracy of 1 % of the load applied to the test piece. The standard followed the Brinell test method using a 10 mm diameter steel ball. The wood test piece was set to the machine table and the steel ball was indented into the surface of the wood piece at a steady and constant force introduced in the machine in order to achieve 1 kN in 15 ± 3 s. The load was maintained for 25 ± 5 s and afterwards the load was removed and the indentation measured. For this purpose images of the test piece’s indentation were acquired immediately after testing with a Olympus SZX-ZB12 stereoscopic microscope and Olympus DP-Soft software. Crossed diameters were measured (d1 and d2) to evaluate the size of the deformation inflicted by the ball (Figure 6). Hardness was on average 56 N/mm2, with a minimum of 31 N/mm2 and a maximum of 113 N/mm2 and most samples corresponding to a hardness class of 50-70 N/mm2. The hardness of cork oak wood is similar to the one found for Portuguese oak wood (Quercus

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faginea) of 50 N/mm2 (Ramos 2009). Softwood boards usually show significantly lower values in the range of 13 to 25 N/mm2. All the obtained hardness values were above 10 N/mm2, a value that is pointed in several European standards related with wood floorings as a minimal value to be attained. The EN 14354 standard gives reference values of hardness for different end-uses. It can be concluded that cork oak wood is suitable for all domestic (including heavy traffic) and moderate commercial end-uses.

Figure 6. Image of hardness test (left) and a close look at the deformation inflicted by the ball (right).

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Wear Resistance There is no specific European standard for measuring wear resistance of solid timber. The existing European standards are related with wear resistance of the finishing layer (lacquer, varnish or other) and are difficult to compare if applied to wood due to differences, e.g. in the abrasive material and the way abrasion is applied (Armstrong 1957; Ohtani and Kamasaki 2005). And so in order to allow the establishment of the type of traffic that will suit cork oak wood, when applied to flooring, a comparison test was carried out by modification of the abrasion test described in the standard EN 14354. This new test was carried out including three well documented species as regards wear resistance (Armstrong 1957): Brachystegia speciformis (Mupanda) suitable for normal traffic ( 63% of total fatty acids), and palmitic acid and linoleic acid concentrations (12-20%).

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Table 1. Variations in the chemical composition of different Holm oak populations. The descriptive statistics are presented according to the mean References Chemical composition [45] [44] [46] Pulp DM (%) 56.72-60.57 68.70-66.00 56.00 Ash (%)1 1.99-1.89 1.50-1.50 1.80-2.00 1 Crude protein (%) 04.48-04.8 4.60-5.40 3.70-5.00 Fiber (%)1 2.71-2.92 5.70-5.90 0.81-1.06 Starch (%)1 59.73-58.28 1 Sugars (%) 5.89-6.84 Crude fat (%)1 10.05-10.76 5.60-7.00 9.50-10.40 C16 (%)2 13.97-14.28 16.30-20.60 C16:1 (%)2 0.12-0.11 2 C17 (%) 0.10-0.10 0.10-0.10 C17:1 (%)2 0.09-0.1 C18 (%)2 3.15-3.28 3.60-3.40 3.30-4.20 C18:1 (%)2 64.99-65.45 56.70-62.90 53.64-62.50 C18:2 (%)2 15.21-15.31 17.70-18.50 12.20-18.20 C18:3 (%)2 0.73-0.81 1.10-1.70 C20 (%)2 0.44-0.46 0.30-0.30 2 C20:1 (%) 0.56-0.57 1 As percent of pulp DM; 2As percent of crude fat.

[6] 63.90-83.60 1.34-2.02 3.90-5.94 8.95-12.47 9.14-14.95 12.15-14.65 64.98-67.81 15.62-17.14 -

These compounds are very important in the pig diet because they affect the Iberian dry ham aging process [41]. Starch was the main acorn component (50%), in contrast with the low protein content (4-6%). A chemosystematic differentiation based on differences in acorn fatty acid composition between Italian and Spanish populations of Q. ilex yielded partial separations of the individual populations [40]. Such separations using acorn fatty acids for

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Jose Valero Galvan, Besma Sghaier-Hammami, Rafael Mª Navarro Cerrillo et al.

native and hybrid populations have also been observed for Q. agrifolia and Q. wislizenii [42]. French Mediterranean evergreen oak populations were reported to be intermediate and heterogeneous in fatty acid profiles between the Spanish and the Italian oak, suggesting a zone of hybridization [39]. Accordingly, we have applied the near-infrared spectroscopy technique to predict a complete chemical analysis of acorn flour in an attempt to compare, catalog, and characterize natural populations of Holm oak from the Andalusia region. Results indicated that there were statistically significant differences in acorn chemical composition between the different Holm oak populations [6]. The analysis showed that northern populations had a tendency to present higher values in acorn weight, length and diameter; in ash, protein, and fat; and in oleic acid content. In contrast, southern population showed lower values in sugar, energy, palmitic and linoleic parameters. Variations in fatty acid levels were observed in different taxa [38, 43] and populations of oaks [39, 40, 42]. Moreover, populations studied on this work seemed to integrate acorn morphology and chemical composition related to environmental conditions of the original provenances. Variations in the acorn chemical composition could be related to factors associated with: (i) weather conditions such as precipitation, temperature and temperature oscillations; (ii) acorn physiological conditions such as ripening or germination; and (iii) sanitary conditions such as desiccation, dampening, rotting and attacks from pests(e.g., Curculio spp., Cydia spp. or phytophages) [44].

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Holm Oak Proteome Given that genetic information is only indicative of the cell’s potential and does not reflect the actual state in a particular cell at a given time, the concept of “proteome” (protein complement expressed by a genome [47]) has emerged. Proteome provides complementary and critical information by revealing the regulation, activities, quantities and interaction of proteins in cells, as well as how their abundance responds to developmental and environmental signals. According to the research objective, different areas within proteomics can be defined (reviewed in [48]), namely: i) descriptive proteomics, including intracellular and subcellular proteomics; ii) differential expression proteomics, iii) post-translational modifications; iv) interactomics; and v) proteinomics (targeted or hypothesis-driven proteomics). The workflow of a standard proteomic experiment includes all or most of the following steps: experimental design; sampling; preparation of tissues, cells or organelles; protein extraction, fractionation or purification; labeling or modification; separation; MS analysis; protein identification and statistical analysis of data and validation (Fig. 2). Previous studies have demonstrated the complexity of a protein extraction’s from vegetable tissues and how the protein solubilization is critical for gel preparation with discrete protein spots that are suitable for MS analysis [21, 48-50]. The most appropriate protocols should be developed for several species [51] and must be optimized for biological systems (e.g., plant species, organs, tissues, cells), as well as for research objectives. In our experience, although phenol extraction is considered to be time-consuming, it generates a high-quality protein extract from a large variety of plant species [51]. The importance of the extraction protocol in proteomic experiments may be summarized in the following statement: only if you can extract and solubilize a protein, will you have the chance to detect and identify it. This is even more important in plant tissues, due to the low protein content compared to other biological

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systems, because of the presence of the cell wall and vacuoles that account the majority of cell mass. Additionally, the presence of proteases and oxidative enzymes, together with the accumulation of large quantities of polysaccharides, lipids, phenolics, and other secondary metabolites, must be taken into account. Currently, the separation and identification of proteins is possible through techniques such as the combination of SDS-PAGE, band cutting, trypsin digestion and LC separation of the resulting peptides, which leaves the proteomic platform capable of providing the best results in terms of protein coverage. Nevertheless, by far, the predominant separation technology used in plant proteomics is still 2-DE, being continuously evaluated and improved. The 2-DE technology is used for separating and displaying components of large protein complexes. As its main advantages, it shows the simplicity, reproducibility, a wide size range (10 kDa to 500 kDa), and both moderately hydrophobic and acidic-basic proteins can be isolated and visualized. It is important to point out the restrictions of gel based techniques, such as a low abundance of proteins, a limited pI range and an absence of membrane proteins, possibly limiting the broad mapping of proteins in plant samples. In order to approach the complexity of the protein’s functional machinery, continuous improvements in techniques and protocols for high-throughput proteomics are being made at all workflow stages. The increasing development of new protocols, platforms and workflows (some of them being quite complex and requiring sophisticated equipment and expertise) has entailed a huge amount of generated data. Some of this data has been deposited and organized in several databases that are available to researchers [48].

Figure 2. Conditions for the preparation of protein extract from plants tissues that are suitable for 2-DE, and different strategies of separation and identification of proteins. Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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Genes, visualized as precise protein bands or spots which reflect physiological status, are good candidates for assessing variability, establishing genetic distances and phylogenetic relationships between different species and individuals, being used in studies with the herbaceous species [52-59]. In forest trees, mainly in the Pinus spp., 2-DE analysis has showed to be a valuable tool which provides informative molecular markers for assessing variability and the establishment of linkage maps [52, 60, 61]. A proteomic research program is being carried out with Quercus ilex subsp. ballota in order to study thevariability of Holm oak populations in Andalusia [1-3]. Jorge et al. [3] reported the first description of the leaf proteome of Holm oak. The biological variance calculated for 100 major spots was of 56%, and it depended on leaf orientation (North, South, East and West), crown position (top, bottom), and the time of leaves collection. As a consequence, it has been almost impossible to use the leaf protein profile in cataloging trees or populations since the intra-population variability can be greater than the inter-population variability. However, four protein spots were found to be significantly different among three provenances [3]. Spots 103 and 104 were only detected in Qi16a seedlings, and were identified as an ATP synthase alpha chain (spot 103) and 2, 3-bisphosphoglycerateindependent phosphoglycerate mutase (spot 104). The two unidentified spots, 101 and 102, were not detected in leaf extracts from the Qi11e provenance, and there were non-significant differences in protein amounts between Qi14a and Qi16a provenances. Furthermore, a study of the variability in Holm oak seeds has been carried out by using SDS-PAGE and 2-DE in ten populations distributed throughout the Andalusia region [7], expected to be less variable than the leaf proteome. Protein content was correlated with acorn size (weight, length and diameter), latitude and altitude data, and average monthly maximum temperatures. The results showed that populations geographically located in the northern areas would be expected to have a higher protein content than those of southern populations. Moreover, it would decrease with the altitude’s location. Finally, the protein content would increase with the mean monthly maximum temperature where the populations are growing. The clustering analysis of acorn protein profiles showed that northern populations separated from southern populations had a tendency to cluster together. The main restriction associated with the approach used is the low number of proteins identified, most of them corresponding to the reserve 11S globulin family of legumins which have a difficult interpretation from a biological point of view. Andalusia Holm oak populations showed a high variability according to the glutelin acorn protein fraction [4]. Finally, the Holm oak’s pollen proteome has been studied as an alternative means to describe natural variability in different populations and interpret it in biological terms, for being a simpler and more stable organ than others such as a leaf or a fruit. A comparison of the pollen protein profiles from four Holm oak populations revealed that 17 protein spots were differentially expressed between them. The multivariate statistical analyses carried out on these variable expressed spots showed that 9 protein species were essential for population discrimination, hence determining their proposition as population markers.

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4. PROTEOMICS IN THE STUDY OF RESPONSES TO ABIOTIC (DROUGHT) Plant proteomic studies published to date have proven to be very useful in characterizing the response to drought stress in different forest tree species [1, 2, 62, 63]. In oak species, these studies have only been performed at the morphological and physiological level [17, 6467]. Moreover, drought effects on morphological and physiological characteristics as predawn leaf water potential, leaf and root relative water content, height and root collar diameter growth and chlorophyll fluorescence were investigated in one-year-old-seedlings obtained from the seed of Holm oak Andalusia populations [1, 2]. Drought stress is associated with a reduced water availability and cellular dehydration. Therefore, changes in cellular metabolism associated with an osmotic adjustment could be expected. Proteome changes upon drought have been studied in oaks [1, 2, 68, 69]. Some differentials that proteins identified belong to enzymes of photosynthesis, and carbohydrate and nitrogen metabolism categories, as well as to the group of stress-related proteins. RubisCO and RubisCO activase were absent under drought conditions. In contrast, a RubisCO small subunit was only present under drought conditions. Furthermore, under drought conditions, globulin and HMW-glutenin and one enzyme involved in carbohydrate metabolism, b-amylase, was induced. Moreover, one fructose–bisphosphate aldolase was enhanced in response to drought conditions. This enzyme is one of the key regulatory glycolytic enzymes [2]. Additionally to the protein reported in the last work, three PSII oxygen-evolving complex (PSII OEC) proteins decreased in intensity in the seedlings which were under drought stress. Triosephosphate isomerases showed lower intensity values in drought and recovered plants than in watered seedlings. One peroxidase increased in intensity in plants stressed by drought conditions, whereas one peroxiredoxin disappeared in water-stressed plants. Other proteins involved in different metabolic pathways were identified, including a glutamine synthetase, quinoneoxido reductase and isoflavone reductase [1]. Changes in the protein profiles, as a consequence of drought stress, in two populations have also been observed after a 28-day-stress-period. Some of the identified proteins that present differences between well-watered and drought seedling were three ATP synthase beta subunits, one photosystem II oxygen- evolving complex protein 2, and a LHCII type I chlorophyll a/b binding protein.

CONCLUSION Different approaches can be used to characterize the natural variability in plant species, from the morphological tools to the modern -omics techniques. However, these have been scarcely used in Quercus ilex. Our research group is a pioneer in this respect. Firstly, we have used a morphometry, and near infrared spectroscopy approach, to study the natural variability in populations of southern Spain. Data showed that northern populations of Q. ilex are different from southern populations in their acorn morphology and chemical composition. Secondly, we have optimized the protein profiles of leaves, acorns and pollen to study the Holm oak’s natural variability. Holm oak leaves present a great variability in the expression level of most of the major proteins and has proven to be useful in the identification of protein spots that can be used as markers for differentiating holm oak provenances. The data obtained

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from acorn protein profiles were used to discriminate and correlate protein profiles with some climate and geographical data. Thirdly, we have used proteomics for studying plant responses to drought. Qualitative changes in the leaf 2-DE protein map have been observed under drought conditions, and these changes can be interpreted in terms of metabolic adaptations to water deficit conditions, including photosynthesis inhibition, mobilization of the protein and carbohydrate reserves, and increased glycolysis.

ACKNOWLEDGMENTS José Valero was a recipient of an Alban Program fellowship (I06D00010MX). This work is part of research projects financed by the Spanish Ministry of Science and Innovation, and cofunded by FEDER: CGL2008-04503-C03-01/BOS, AGL2002-00530, and AGL200912243-C02-02.

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Chapter 8

OAKS AND MYCORRHIZAL FUNGI Darlene Southworth

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ABSTRACT In all species of Quercus, fine roots in the upper soil layers are ectomycorrhizal. Oak root tips are coated with a mantle of fungal tissue, and the role of root hairs is replaced by fungal hyphae extending into the soil. Oak mycorrhizal fungi include species in the Ascomycota and Basidiomycota; fruiting body forms include epigeous sporocarps and resupinate crusts that produce airborne spores and hypogeous sporcarps with spores dispersed by animal mycophagists. Acorns germinate and initiate a taproot that is not mycorrhizal, subsequently lateral roots become available for mycorrhiza formation. Seedlings within oak woodlands or near the margin of mature oaks may encounter hyphae from the mycorrhizal network of mature trees. Seedlings outside the extent of the root-hyphal network of mature trees may obtain inoculum from dispersed spores—either airborne or from mycophagous animals. Seedlings without mycorrhizas may survive one or two years, but roots of saplings become mycorrhizal. Oaks grown in glasshouse or nursery conditions may not immediately require mycorrhizas; in addition to the nutrients stored in cotyledons, water and fertilizer decrease their reliance on mycorrhizal fungi or decrease formation of mycorrhizas. Chance encounters with spores may inoculate managed oak seedlings, allowing them to increase growth in nursery conditions, but creating uncertain success when outplanted. The ability of oaks to respond to global warming by moving to higher elevations or to more northerly latitudes will depend on dual dispersal of acorns and of spores of mycorrhizal fungi.

INTRODUCTION The first descriptions of oak mycorrhizas date from the 1885 paper of A. B. Frank (for translation, see B. Frank 2005). These descriptions refer to ectomycorrhizas, which form a mantle around tips, a network of hyphae (the Hartig net) around epidermal cells, and

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emanating hyphae or hyphal strands that extend from the mantle into the soil (Smith and Read 2008). “The question of the species of the root fungi” was raised even then. Direct linkage of sporocarps to particular mycorrhizal morphotypes is rarely possible because connecting hyphae are too thin and rhizomorphs rare. The fruiting season for macrofungi is relatively short compared with the duration of mycorrhizas, and the number of mycorrhizal morphotypes per tree exceeds the number of sporocarps at that tree. Macrofungal surveys conducted in a stand of trees over all seasons and many years, with obvious saprotrophs subtracted, will include mycorrhizal species, but will not identify those mycorrhizal fungal species that lack epigeous sporocarps (e.g., resupinate and hypogeous fungi), and will not correlate fruiting species with particular morphotypes or with mycorrhizal abundance (e.g., Schmidt et al. 1999). Identification of ectomycorrhizas to “morphotype,” as a stand in for species, has been taken to a high art by Agerer (1987-2008, 1991; Agerer and Rambold 2004–2007) and utilized by Goodman et al. (1996). Initially, at least, some morphotypes were ascribed to pseudogenera such as “Querceirhiza”. The detailed microscopic examination required for precise sorting of mycorrhizal tips is too time-consuming for large samples and too inaccurate for inexperienced observers. With the advent of standardized protocols for the polymerase chain reaction (PCR), restriction fragment-length polymorphisms (RFLPs) added the additional characters of DNA fragment lengths produced by endonucleases (Gardes and Bruns 1993, 1996). This approach was best suited to determinations of species richness, to comparisons of closely related sites or treatments, and to root samples in areas for which collections of identified sporocarps were available. However, lack of a standardized suite of endonucleases and absence of a central database limited cross-site comparisons, even with better data analysis (Dickie et al. 2003). Refined methods including t-RFLPs increased the efficiency of the process but still required identified sporocarps for comparison (Burke et al. 2005, Dickie and FitzJohn 2007). The availability of genetic sequencing and the expansion of GenBank (http://www. ncbi.nlm.nih.gov/genbank/), EMBL (http://www.ebi.ac.uk/embl/Contact /collaboration.html), and other accessible databases along with the widespread use of sequences from the internal transcribed spacer (ITS) and large subunit (LSU or 28S) genes have facilitated identification of mycorrhizal fungi to taxonomic levels from species to phylum and have enabled cross-site comparisons of mycorrhizal communities (White et al. 1990, Egger 1994, Bruns et al. 1998, Horton and Bruns 2001).

PATTERNS OF MYCORRHIZAL ASSOCIATIONS Ectomycorrhizal assemblages. Based on published species lists determined by DNA sequencing, we compare the ectomycorrhizal communities on a variety of oak species (Avis et al. 2003; Valentine et al. 2004; Richard et al. 2005; Walker et al. 2005; Smith et al. 2007; Avis et al. 2008; Courty et al. 2008; Morris et al. 2008a, b; Frank et al. 2009; Morris et al. 2009; Moser et al. 2009; Richard et al. 2011). Oak species share fungal taxa (Table 1). Among the Ascomycota, Cenococcum geophilum, Tuber species, and many genera in the Pezizales are widely shared. Of these, 76% are hypogeous with fruiting bodies produced underground and spores dispersed by animal mycophagists. In the Basidiomycota, species in

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the genera Lactarius, Russula, Cortinarius, Amanita, Hebeloma, and Inocybe along with species in the Thelephoraceae and Sebacinales are widespread among oaks of diverse habitats. Of these taxa, 18% are hypogeous and another 18% resupinate, forming crusts on soil or woody debris. Species richness appears to vary, but the studies differed in the extent of sampling. Uncertainty about species identification by GenBank limits that comparison. A comparison of mycorrhizal communities as in Table 1 suggests areas for closer comparison as more molecular information becomes available. Other mycorrhizal types. In addition to ectomycorhizas, oak roots also form vesiculararbuscular mycorrhizas (VAMs, also known as endomycorrhizas) with fungi in the phylum Glomeromycota, e. g., Glomus (Smith and Read 2008). VAMs have intraradical hyphae between root cortical cells, and produce arbuscules within root cortical cells and thick-walled vesicles within the cortex (Grand 1969). Ectomycorrhizas and endomycorrhizas have been observed simultaneously in Quercus agrifolia and Q. garryana in natural settings, in Q. imbricaria in a tree nursery, and in Q. rubra from natural settings and from germinated seedlings outplanted near Q. montana and Acer rubrum (Grand 1969, Rothwell et al. 1983, Dickie et al. 2001, Egerton-Warburton and Allen 2001, Valentine et al. 2002). Ericoid mycorrhizal fungi (Oidiodendron species) have been reported in roots of Q. ilex (Bergero et al. 2000). Mycorrhizal networks. Networks of fungal hyphae linking mycorrhizas among host plants of the same or different species are well documented for both arbuscular and ectomycorrhizas (Simard et al. 1997, Simard and Durall 2004). The presence of the same fungal species on multiple oak trees indicates potential mycorrhizal networks in oak woodlands (Southworth et al. 2005). Shared mycorrhizal species among oaks and other species such as Cercocarpus ledifolius suggest a mycorrhizal network linking oaks with EM hosts of diverse species (McDonald et al. 2010). Stable isotopes of nitrogen (15N) applied to sapling needles of Pinus sabiniana moved to sapling roots and leaves of Quercus douglasii separated by one meter within four weeks, providing evidence of actual transfer to oaks via underground routes (He et al. 2006).

MYCORRHIZAL PROCESSES It is difficult to determine precisely the importance of mycorrhizal fungi to oaks. Because all oaks appear to be mycorrhizal with a relatively broad range of fungi, there are likely to be diverse roles for the fungi and multiple effects or benefits to the hosts. Glasshouse studies give some indication of the response of seedlings to fungal inoculum; outplanting experiments extend this observation, but both are limited by very restricted mycorrhizal communities and by the short-term nature of the responses by long-lived host trees. In natural conditions, oak mycorrhizas must respond to interacting mycorrhizal fungi and to extremes of water availability including hydraulic lift, and diverse other factors such as leaf endophytes and leaf-eating insects, and develop interdependence with saprotrophic fungi for biogeochemical cycling. Furthermore, host trees of the same and different species may be connected via mycorrhizal networks.

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Table 1. Mycorrhizal fungi identified by DNA sequencing on Quercus crassifolia (cr), Q. laurina (la), Q. ilex (il), Q. douglasii (do), Q. wislizeni (wi), Q. petraeus (pe), Q. robur (ro), Q. ellipsoidalis (el), Q. macrocarpa (ma), Q. alba (al), Q. rubra (ru), Q. prinus (pr), and Q. garryana (ga). Fruiting body (fb) morphology is epigeous (e), hypogeous (h), or resupinate (r) cr1,

Quercus species

la2

il3,4

do5,6

wi6

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2

Fungal taxon Ascomycota Cenococcum Tuber Genea Helvella Pachyphloeus Peziza infossa Tarzetta Genabea Otidia Balsamia Cazia Geopora Gilkeya Hydnoplicata Marcellinia Trichophaea Basidiomycota Lactarius Russula Sebacinales Thelephoraceae Cortinarius Amanita Hebeloma Inocybe Clavulinaceae Laccaria Entoloma Hygrophorus Tricholoma Xerocomus Cantharellaceae Scleroderma Atheliaceae Boletus Clavariaceae Albatrellus Boletellus Corticiaceae Gautieria Gymnomyces Hydnellum Hydnobolites Hydnum Melanogaster Antrodiella

pe/ ro7

el/ ma8

al/ ru9,10

pr10

1 1

1 1

1 1 1 1

1 1

ga11,1

Sum

2,13

Fb h h h e h h h h e h h h h h h e

1 1 1 1 1

e e r r e e e e e e e e e e e h r e e e e r h h e h e h r

1 1 1 1 1 1

1 1 1

1 1 1

1

1

1 1 1 1 1 1 1 1 1

1 1 1 1 1

1 1 1

1 1

1 1 1 1 1 1 1

1 1

1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1

1 1 1 1

1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1

1 1

1 1 1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1 1 1 1 1

1 1

1 1 1 1 1 1 1 1 1 1 1

1

1 1 1 1 1 1 1

1 1 1

1 1 1

1 1 1 1 1 1 1

1 1 1

1

1

1 1 1 1 1 1 1

1 1

1 1

1 1 1

1 1

1 1 1

1 1

1

1

1

1 1

1

1

1 1

1 1

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10 10 6 5 3 3 3 2 2 1 1 1 1 1 1 1 10 10 10 10 10 8 8 8 7 7 5 5 5 5 4 4 3 3 3 2 2 2 2 2 2 2 2 2 1

211

Oaks and Mycorrhizal Fungi cr1,

Quercus species

la2

il3,4

do5,6

wi6

2

Astraeus Clitopilus Coltricia Elaphomyces Gyroporus Hysterangium Leccinum Octaviania Ramaria Rhizopogon Sistotrema Total taxa

e e r h e h e h e h r

pe/ ro7

el/ ma8

al/ ru9,10

pr10

ga11,1 1

1 1 1 1 1 1 1 1 1 1 24

19

17

25

23

23

14

24

Sum

2,13

14

1 1 1 1 1 1 1 1 1 1 1

24

1

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Morris et al. 2008a. 2 Morris et al. 2009. 3 Richard et al. 2005. 4 Richard et al. 2011. 5 Smith et al. 2007. 6 Morris et al. 2008b. 7 Courty et al. 2008. 8 Avis et al. 2003. 9 Avis et al. 2008. 10 Walker et al. 2005. 11 Moser et al. 2009. 12 Valentine et al. 2004. 13 Frank et al. 2009.

Glasshouse studies. Although responses of Quercus seedlings inoculated with a single fungus species that are positive, negative, or neutral may have no relevance to the responses of saplings or mature trees to that fungal species in nature, glasshouse studies provide some measure of the importance of mycorrhizal fungi to oaks (Garrett et al. 1979). In containerized seedlings of Q. robur, Q. alba, and Q. velutina inoculated with Pisolithus tinctorius, Suillus granulatus, S. luteus, Cenococcum geophilum, or Thelephora terrestris, the effects of individual fungal species varied, but inoculated seedlings of all oak species were taller with a larger diameter root collar, greater leaf area, and greater root and shoot dry weights (Dixon et al. 1984, Daughtridge et al. 1986). Foliar nutrient content (K, Ca, Mg, Fe, B, Mn, Zn, Cu, and Mo) was also higher (Mitchell et al. 1984). When inoculated seedlings were planted out, seedlings with Pisolithus tinctorius mycorrhizas continued to show growth greater than that of uninoculated controls over one growing season (Dixon et al. 1981). Glasshouse experiments also demonstrate the effects of mycorrhizas on water relations for host plants. When outplanted, seedlings of Q. velutina with established mycorrhizas of Pisolithus tinctorius showed higher water potentials, less fluctuation between predawn and noon water potentials, and less depression of water potential during drought periods (Dixon et al. 1983). Soil-plant resistance to water transfer was also lower in mycorrhizal seedlings. In contrast to the uptake of water by mycorrhizal fungi, oak roots also provide water from deep sources to fungi via hydraulic lift, a process by which deep tree roots take up water, particularly as surface soil dries (Dawson 1996, Millikin and Bledsoe 2000). Hydraulic lift is driven by osmotic pressure in the roots at night when leaf stomata are closed. This water under pressure can be transferred via mycorrhizal hyphae to other plants (Querejeta et al.

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2003, Egerton-Warburton et al. 2007, Querejeta et al. 2009). Thus under some conditions fungal hyphae transfer water to roots, while under other conditions, roots transfer water to fungi. Nursery experiments. Acorns planted directly into prepared soil in nursery beds more closely approach natural conditions with regard to the seasonality and variability of light and temperature. Acorns of Q. rubra sown into beds treated with mycelium of Suillus luteus developed mycorrhizas in the first growing season. Late in the first growing season, uninoculated seedlings formed mycorrhizas from native fungal sources including Hebeloma sp., Inocybe sp., Laccaria laccata, Thelephora terrestris, and Cenococcum geophilum and from S. luteus (Dixon and Johnson 1992). Height of Q. garryana seedlings growing in a nursery bed correlated with root biomass, with total mycorrhizal abundance (including Laccaria and Tuber species), and with abundance of Laccaria mycorrhizas (Southworth et al. 2009). Native oak seedlings from nearby Q. garryana woodlands were mycorrhizal with 11 fungal species, none of which occurred on the nursery seedlings. Seedlings in nursery beds may form mycorrhizas without specific inoculation, although the species of mycorrhizal fungi on nursery seedlings are not the same as those of native seedlings. Experiments in natural habitats. Acorn germination and seedling growth in natural settings acquire another level of complexity in response to factors such as soil structure and composition, water sources, and interactions with other plants and with animals. Whether dispersed as natural regeneration of oak woodlands or hand planted for a restoration program, seedlings obtain mycorrhizal inoculum for lateral roots in the first or second growing season (Frank et al. 2009). Because oak seedlings and mycorrhizal fungi are obligate mutualists, both symbionts must disperse to the same place within a limited time frame. Possible mechanisms for dispersal of mycorrhizal inoculum include seedling root contact with hyphae from the mycorrhizal network of mature trees, dispersal of fungal spores via animal feces, and airborne dispersal of spores. If mycorrhizal inoculum comes from the mycorrhizal network of mature trees, then the assemblage of mycorrhizas on seedlings should be a subset of the ectomycorrhizal species on mature trees, and seedling success should be greater near established trees. If small mammals disperse mycorrhizal fungal spores, then seedlings beyond the root zone of mature trees would develop mycorrhizas, and these fungi would be predominately hypogeous. If mycorrhizal inoculum arrives as airborne spores, then epigeous fungi would predominate on seedlings beyond the root zone of mature trees. In Q. rubra, seedlings near the edge of a mature stand developed mycorrhizas, but mycorrhizal colonization declined beyond that distance (Dickie and Reich 2005; Dickie et al. 2002, 2007b). In Q. garryana, mycorrhizas of seedlings planted closest to mature trees (within 10 m) had the richest fungal diversity (Frank et al. 2009). First-year seedlings planted beyond the mycorrhizal network of parent trees (>10 m from trees) formed mycorrhizas with hypogeous fungal species (Tuber sp., Geopora sp., Peziza infossa) that were also found as spores in rodent fecal pellets. These results show overlapping sources of mycorrhizal inoculum: mycorrhizas of established trees, rodent-dispersed spores from hypogeous fruiting bodies near the trees, and airborne spores of epigeous fungi. Mycorrhizal networks may account for the greater success of seedlings near the root zone of mature trees (Dickie et al. 2007a). Because restoration sites frequently are not located near mature trees, the question arises about how to provide inoculum to oak seedlings. There is a time delay from acorn germination to the development of lateral roots, which can become mycorrhizal. Thus

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treatments applied at the time of acorn planting must wait months to become active. When forest soil, collected from under the canopy of mature Q. ellipsoidalis, was transferred to holes in which acorns were planted, mycorrhizal infection was higher than controls in year one; leaf mass and foliar N concentrations were higher in year two, and budbreak was earlier (Dickie et al. 2007a). Forest soils added to planting holes of Q. lobata correlated with greater ectomycorrhizal fungal diversity and with an increase in shoot growth after one growing season (Berman and Bledsoe 1998). Modification of the natural environment—N addition. In experiments in which N was added to oak woodlands, either short term (1-3 yr) or long term (16 yr), ectomycorrhizal communities differed slightly (Avis et al. 2003, 2008). On N-enriched sites in woodlands of Quercus alba/Q. rubra and of Q. macrocarpa/Q. ellipsoidalis, species accumulation curves were flatter with less total biodiversity, and communities of mycorrhizal fungi differed in composition. In urban soils with higher anthropogenic N deposition rates, fewer mycorrhizal fungal species were observed on seedlings and on mature trees of Q. rubra (Baxter et al. 1999). Natural experiments—serpentine soils. To determine the role of soil composition on mycorrhizal communities with Quercus garryana, we compared mycorrhizal communities at sites with serpentine (rich in iron, magnesium, and heavy metals) and nonserpentine soils. The same most abundant and most frequent mycorrhizal species, Cenococcum geophilum, Tuber candidum, Genea harknessii, Tomentella sp., Sebacina sp., and Inocybe sp., were found on both serpentine and nonserpentine soils; mycorrhizal communities on serpentine and nonserpentine soils were similar (Moser et al. 2005, 2009).

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PREDICTIONS Oak regeneration. In order for oaks to grow from acorns, whether as replacement trees within an oak stand, as extensions to the margin of an oak forest or woodland, or as restoration plantings in sites not currently occupied by oaks, there must be dual dispersal of acorns and mycorrhizal inoculum—either spores or hyphae. Because the source of fungi can vary, we can predict several aspects of dual dispersal: Near mature oaks within a stand or at the edge of the stand, the most likely source is the existing community of mycorrhizal fungi. From the edge of a stand outward for many meters, small mammals may disperse fungal spores of hypogeous fungi that grow under the mature stand (Frank et al. 2006, 2009). The benefit of this is that small mammals eat many spores, thus an abundance of spores of diverse mating types can reach seedlings. Shrub facilitation of seedling establishment is well known in oaks (Calloway 1992; Dickie and Reich 2005, Williams et al. 2006). Because small mammals visit shrubs for protection and for food sources, they may promote mycorrhiza formation on seedlings under shrubs. Epigeous spores mostly fall within a few meters of the mature sporocarp, but some may disperse via air currents and eventually inoculate seedling roots. Thus most oak seedlings will develop near mature trees, and a stand of oaks may enlarge or “move” at the rate of growth of fungal hyphae. Response of oaks to global warming. In North America, Quercus garryana reaches its northernmost extent in southern coastal British Columbia. Global climate change patterns predict that warmer and drier conditions will move the habitat available to oaks to higher

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elevations and more northerly latitudes where woodlands adjoin conifers (Hamann and Wang 2006, Hosten et al. 2006, Parmesan 2006, Devine et al. 2007, IPCC 2007, Thompson 2007). Whether oaks, especially those adapted to seasonally dry Mediterranean climates, expand into new habitats will depend on their ability to establish beyond the margins of existing woodlands (Crawford 2008). The importance of mycorrhizas in seedling success has largely been ignored. Recent studies on oak seedling survival and response to drought have not considered the mycorrhizal influence, yet that factor may make all the difference (Fuchs et al. 2000, Quero et al. 2006, Tyler et al. 2006, Valladares and Gianoli 2007).

CONCLUSION All oak species are mycorrhizal with diverse fungi. This mutualistic symbiosis appears to be essential for oak survival from the seedling stage through maturity. For oaks to regenerate from seed, either in natural habitats or at restoration sites, seedlings must encounter mycorrhizal inoculum—as spores or hyphae. For seedlings near mature trees, the existing mycorrhizal network on roots is accessible. Beyond that or in areas lacking mature oaks, mycorrhizal inoculum may be dispersed as spores of hypogeous fungi in small mammal fecal pellets or as airborne spores of epigeous fungi. This dual dispersal of seeds and spores will be essential for oaks to respond to global climate change by moving upward in elevation and northward.

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Egerton-Warburton LM, Allen MF 2001 Endo- and ectomycorrhizas in Quercus agrifolia Nee. (Fagaceae): patterns of root colonization and effects on seedling growth. Mycorrhiza 11:283-290. Egerton-Warburton LM, Querejeta JI, Allen MF 2007 Common mycorrhizal networks provide a potential pathway for the transfer of hydraulically lifted water between plants. Journal of Experimental Botany 58:1473-1483. Egger KN 1995 Molecular analysis of ectomycorrhizal fungal communities. Canadian Journal of Botany 73(Suppl 1):S1415-1422. Frank B. 2005 On the nutritional dependence of certain trees on root symbiosis with belowground fungi (an English translation of A.B. Frank’s classic paper of 1885). Mycorrhiza 15:267-275. Frank JL, Anglin S, Carrington EM, Taylor DS, Viratos B, Southworth D 2009 Rodent dispersal of fungal spores promotes seedling establishment away from mycorrhizal networks in Quercus garryana. Botany 87:821-829. Frank JL, Barry S, Southworth D 2006 Mammal mycophagy and dispersal of mycorrhizal inoculum in Oregon white oak woodlands. Northwest Science 80:264-273. Fuchs, M.A., Krannitz, P.G., and Harestad, A.S. 2000. Factors affecting emergence and firstyear survival of seedlings of Garry oaks (Quercus garryana) in British Columbia, Canada. Forest Ecology and Management 137:209-219. Gardes M, Bruns TD 1993 ITS primers with enhanced specificity for basidiomycetes— application to the identification of mycorrhizas and rusts. Molecular Ecology 2:113-118. Gardes M, Bruns TD 1996 ITS–RFLP matching for identification of fungi. In Methods in Molecular Biology, Species Diagnostics Protocols: PCR and Other Nucleic Acid Methods V 50, Clapp JP (ed). Humana Press, NJ. Pp 177–186. Garrett HG, Cox GS, Dixon RK, Wright GM. 1979. Mycorrhizae and the artificial regeneration potential of oak. In Regenerating oaks in upland hardwood forests, Fischer BC, Holt HA (eds), John S. Wright Forest Conference Proceedings. Purdue University, West Lafayette, IN. Pp 82-90. Available from http://www.uky.edu/~jmlhot2/Resources/ Proceedings%20Regenerating%20Oaks%20in%20Upland%20Hardwood%20Forests.pdf. Accessed 2 Sep 2011. Goodman DM, Durall DM, Trofymow JA, Berch SM 1996 A manual of concise descriptions of North American ectomycorrhizas. Mycologue Publications, Sidney, Australia. Grand LF 1969 A beaded endotrophic mycorrhiza of northern and southern red oak. Mycologia 61:408-409. Hamann A, Wang T 2006 Potential effects of climate change on ecosystem and tree species distribution in British Columbia. Ecology 87:2773-2786. He XH, Bledsoe CS, Zasoski RJ, Southworth D, Horwath WR 2006 Rapid nitrogen transfer from ectomycorrhizal pines to adjacent ectomycorrhizal and arbuscular mycorrhizal plants in a California oak woodland. New Phytologist 170:143-151. Horton TR, Bruns TD 2001 The molecular revolution in ectomycorrhizal ecology: peeking into the black-box. Molecular Ecology 30:1855-1871. Hosten PE, Hickman OE, Lake FK, Lang FA, Vesely D 2006 Oak woodlands and savannas. In Restoring the Pacific Northwest, Apostol D, Sinclair M (eds). Island Press, Washington, DC. Pp. 63-96.

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[IPCC] Intergovernmental Panel on Climate Change 2007. Climate Change 2007 Synthesis Report. Available from http://www.ipcc.ch/publications _and_data/ar4/syr/en/contents. html. Accessed 10 Sep 2011. Marsico T, Hellmann JJ, Romero-Severson J 2009 Patterns of seed dispersal and pollen flow in Quercus garryana (Fagaceae) following postglacial climatic changes. Journal of Biogeography 36:929-941. McDonald KR, Pennell J, Frank JL, Southworth D 2010 Ectomycorrhizas of Cercocarpus ledifolius (Rosaceae). American Journal of Botany 97:1867-1872. Millikin Ishikawa C, Bledsoe CS 2000 Seasonal and diurnal patterns of soil water potential in the rhizosphere of blue oaks: evidence for hydraulic lift. Oecologia 125:459- 465. Mitchell RJ, Cox GS, Dixon RK, Garrett HE, Sander IL 1984 Inoculation of three Quercus species with eleven isolates of ectomycorrhizal fungi. II. Foliar nutrient content and isolate effectiveness and seedling growth relationships. Forest Science 30:563–572. Morris MH, Pérez- Pérez MA, Smith ME, Bledsoe CS 2008a Multiple species of ectomycorrhizal fungi are frequently detected on individual oak root tips in a tropical cloud forest. Mycorrhiza 18:375-383. Morris MH, Pérez- Pérez MA, Smith ME, Bledsoe CS 2009 Influence of host species on ectomycorrhizal communities associated with two co-occurring oaks (Quercus spp.) in a tropical cloud forest. Federation of European Microbiological Societies Microbiology Ecology 69:274-287. Morris MH, Smith ME, Rizzo DM, Rejmánek M, Bledsoe CS 2008b Contrasting ectomycorrhizal fungal communities on the roots of co-occurring oaks (Quercus spp.) in a California woodland New Phytologist 178:167-176. Moser AM, Petersen CA, D’Allura JA, Southworth D 2005 Comparison of ectomycorrhizas of Quercus garryana (Fagaceae) on serpentine and nonserpentine soils in southwestern Oregon. American Journal of Botany 92:224-230. Moser AM, Frank JL, D’Allura JA, Southworth D 2009 Mycorrhizal communities of Quercus garryana on serpentine soils exhibit edaphic tolerance. Plant and Soil 315:185-194. Parmesan C 2006 Ecological and evolutionary responses to recent climate change. Annual Review of Ecology, Evolution and Systematics 37:637-669. Querejeta JI, Egerton-Warburton L, Allen MF 2003 Direct nocturnal water transfer from oaks to their mycorrhizal symbionts during severe soil drying. Oecologia 134: 55-64. Querejeta JI, Egerton-Warburton LM, Allen MF 2009. Differential access to groundwater modulates the mycorrhizal responsiveness of oaks to inter-annual rainfall variability in a California woodland. Ecology 90:649-662. Quero JL, Villar R, Marañón T, Zamora R 2006 Interactions of drought and shade effects on seedlings of four Quercus species: physiological and structural leaf responses. New Phytologist 170:819-834. Richard F, Millot S, Gardes M, Selosse MA 2005 Diversity and specificity of ectomycorrhizal fungi retrieved from an old-growth Mediterranean forest dominated by Quercus ilex. New Phytologist 166:1011-1023. Richard F, Roy M, Shahin O, Sthultz C, Duchemin M, Joffre R, Selosse MA 2011 Ectomycorrhizal communities in a Mediterranean forest ecosystem dominated by Quercus ilex: seasonal dynamics and response to drought in the surface organic horizon. Annals of Forest Science 68:57-68.

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Rothwell FM, Hacskaylo E, Fisher D 1983 Ecto- and endomycorrhizal fungus associations with Quercus imbricaria L. Plant and Soil 71:309-312. Schmidt JP, Murphy JF, Mueller GM 1999 Macrofungal diversity of a temperate oak forest: a test of species richness estimators. Canadian Journal of Botany 77:1014-1027. Simard SW, Durall DM 2004 Mycorrhizal networks: a review of their extent, function, and importance. Canadian Journal of Botany 82:1140–1165. Simard SW, Perry DA, Jones MD, Myrold DD, Durall DM, Molina R. 1997. Net transfer of carbon between ectomycorrhizal tree species in the field. Nature 388:579–582. Smith ME, Douhan GW, Rizzo DM 2007 Ectomycorrhizal community structure in a xeric Quercus woodland based on rDNA sequence ananlysis of sporocarps and pooled roots. New Phytologist 174:847-863. Smith SE, DJ Read 2008 Mycorrhizal symbiosis, 3rd ed. Academic Press, Cambridge, UK. Southworth D, Carrington EM, Frank JL, Gould P, Harrington CA, Devine WD 2009 Mycorrhizas on nursery and field seedlings of Quercus garryana. Mycorrhiza 19:149158. Southworth D, He XH, Bledsoe CS, Horwath WR 2005 application of network theory to potential mycorrhizal networks Mycorrhiza 15:589-595. Tyler CM, Kuhn B, Davis FW 2006 Demography and recruitment limitations of three oak species in California. Quarterly Review of Biology 81:127-152. Valentine LL, Fiedler TL, Haney SR, Berninghausen HK, Southworth D 2002 Biodiversity of mycorrhizas on Garry oak (Quercus garryana) in a southern Oregon savanna [online]. In Oaks in California’s changing landscape. Proceedings of the Fifth Symposium on Oak Woodlands, Standiford RB, McCreary D, Purcell KL (eds). USDA Forest Service Gen. Tech. Rep. PSW-GTR-184. Pp. 151–157. Available from http://www.fs.fed.us/psw /publications/documents/psw_gtr184. Accessed 1 Sep 2011. Valentine LL, Fiedler TL, Hart AN, Peterson CA, Berninghausen HK, Southworth D 2004 Diversity of ectomycorrhizas associated with Quercus garryana in southern Oregon. Canadian Journal of Botany 82:123-135. Valladares F, Gianol, E 2007 How much ecology do we need to know to restore Mediterranean ecosystems? Restoration Ecol. 15:363-368. Walker JF, Miller OK Jr, Horton JL 2005 Hyperdiversity of ectomycorrhizal fungus assemblages on oak seedlings in mixed forests in the southern Appalachian Mountains. Molecular Ecology 14:829-838. White TJ, Bruns T, Lee S, Taylor J 1990 Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In PCR Protocols: a guide to methods and applications, Innis MA, Gelfand DH, Sninsky JJ, White TJ (eds). Academic Press, New York. Pp 315-322. Williams K, Westrick LJ, Williams BJ 2006 Effects of blackberry (Rubus discolor) invasion on oak population dynamics in a California savanna. Forest Ecology and Management 228:187-196.

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In: Oak: Ecology, Types and Management Editors: C. Aleixo Chuteira and A. Bispo Grão

ISBN 978-1-61942-492-0 © 2012 by Nova Science Publishers, Inc.

Chapter 9

COMPARATIVE STUDY OF PHYSIC-CHEMICAL CHARACTERIZATION AND MICROBIAL ADHESION OF OAK WOOD WITH OTHER WOOD SPECIES Soumya El Abed1,2, Saad koraichi Ibnsouda1,2 and Hassan Latrache3 1

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Laboratory of Microbial Biotechnology. Faculty of Science and Technics, Fez. Morocco 2 Regional University Center of Interface. University Sidi Mohamed Ben Abdellah, Fez. Morocco 3 Laboratory of Valorization and Security Food Products. Faculty of Science and Technics, Beni Mellal. Morocco

ABSTRACT On any surface in a non-sterile aqueous (or very humid) environment, biofilm can formed. The microbial adhesion to surfaces such as plastics, polypropylenes, rubbers, stainless steel and glass is now well established. However, on wooden surfaces; very few studies have been focused on the interactions of wood and microorganisms. In this chapter, the first part describes –brieflymicrobial biofilm step. In the second and the third parts, respectively, the roles of the material surface and the microbial adhesion of wood and the biofilm development are discussed. Comparative data of the hydrophobicity, electron donor-acceptor, Lifshitz–van der Waals components for oak, cedar, beech, ash, pine and teak are presented. As far as we know, the theoretical prediction of microbial adhesion on wood species as mentioned has not been reported in the literature yet. Therefore, the comparison of the theoretical adhesion of these species are finally addressed.

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1. INTRODUCTION

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Wood is an important renewable and natural resource with a multitude of uses. Especially, oak wood was traditionally used for in-ground applications such as vineyard poles, fences, and other infrastructure without any chemical protection. Nowadays, oak is predominately used for other outdoor applications with higher added value such as garden furniture, children playground equipment, decking, etc. Unfortunately, related to civil engineering, microbial growth in biofilm on surfaces is frequently associated with aesthetical degradation, risk of biodeterioration [1-3] or health risks caused by mycotoxins [4]. Therefore, the presence of a microorganism can deteriorated wood, but the greatest damage is caused by fungi. In this context, different degradation patterns of wood by bacteria and fungi were published [5-8]. However, over the last 20 years or so we’ve been realizing that even microorganism don’t always live alone. Biofilms generally form on any surface in a non-sterile aqueous (or very humid) environment. Instead, more than 99 percent of all microorganisms as attached to each other known as biofilms. Biofilms are formed by adhesion of bacterial cells to surfaces through an exopolymeric matrix. A biofilm can be defined an assemblage of microbial cells that is irreversibly associated with a surface and enclosed in a matrix of primarily polysaccharide material. Microbial adhesion and biofilm formation is a complex process involving several steps. The initial step for adhesion of bacteria onto surfaces is the adsorption of conditioning components, attachment of proteins, and then of single cells to the surface. The second stage involves microbial transport and co-aggregation including reversible adhesion of single organisms and of microbial co-aggregates. Usually, microbial adhesion is described in two separate stages: the “reversible adhesion” and the “irreversible adhesion”. Different microorganism/surface physical–chemical and chemical interactions are thought to be involved in these two stages (Figure 1).

Figure 1. Scheme of the biofilm development. Details of the step 2 (“bacteria adhesion”).

The next step is the anchoring and establishment of biofilm on the surface followed by growth of cells on the surface. At this point irreversible adhesion has been established through exopolymeric substance (EPS) production. In a mature biofilm there is also a balance between attachment and detachment of cells [9-10].

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The adhesion of these micro-organisms, however, leads to the degradation of wood. On wooden surfaces; no studies have been focused on the interactions of oak wood and microorganisms. It has been recognized that a better understanding of the interactions between microbial biofilms and the oak surfaces may play a significant role to control this problem and may help in the development of strategies to reduce their adherence to this type of substratum. Therefore, there is a clear need for systematic investigation of the microbiological ecosystems on wooden oak surfaces and for quantifying total interaction free energy between them. In this chapter we describe the prediction of microbial adhesion on oak wood specie using thermodynamic approach. The physicochemical proprieties in term of hydrophobicity and the lifshitz-van der waals component as well as electron donor and electron acceptor of oak wood were also compared with other wood species (Cedar, beech, ash, pine, teak).

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2. WOOD SPECIES SURFACES CHARACTERIZATION Several techniques are usually employed to assess surface wood properties. Hydrophobicity called also wettability can be measured by contact angle measurements. The Wilhelmy plate method was shown to be especially appropriate for such a heterogeneous and porous material as wood is [11]. There are various approaches to determine the wood surface energy and its components. The most known ones are those of Zisman, Owens-Wendt-RabelKaelble and Oss-Chaudhury-Good [12-14]. Especially, the contact angle of a liquid on a solid surface provides direct information about the hydrophobicity and electron-donor proprieties of the surface. However, several authors have recently studied the surface properties of different biological systems and materials. Since the work of Kalnins et al. [15] numerous investigations have been carried out on wood surfaces. Gardner et al. [16] found dynamic contact angle measurements to be useful for monitoring wood processing and environmental conditioning effects on surface energetics. Boehme and Hora [17] reported water absorption and contact angles on different European, North American and tropical wood species. Shen et al. [18] presented a systematic study of surface free energy and acid–base properties of pine (Pinus sylvestris L.); for evaluation of the data the Lifshitz–van der waals/acid–base (LW–AB) approach was applied. Gindl et al. [12] compared the applicability of different approaches to determine the surface free energy of wood and found the LW–AB approach to be the most effective among the generally accepted models. A detailed overview of literature data obtained on wood surfaces was presented by de Meijer et al. [19].

2.1. Wood Surface Hydrophobicity Many studies have described adhesion in terms of physicochemical parameters such as hydrophobicity [20-21], and surface energy [22].

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Soumya El Abed, Saad koraichi Ibnsouda and Hassan Latrache

We report here the comparison of hydrophobicity proprieties of oak wood with cedar, beech, pine, ash, and teak wood species. The hydrophobicity behaviors are presented in figure (2,3,4 and 5). According to Vogler (1998) [23], hydrophobic surfaces exhibit a water contact angle values higher than 65°, whereas hydrophilic ones exhibit water contact angle values lower than 65°. However, with this approach it is only possible to assess hydrophobicity qualitatively, Oliveira et al. [24]. Taking into account the values of water contact angles, it can be seen that that oak, cedar and ash wood exhibit hydrophobic character ( w > 65°) (Figure 2). The other wood species (Beech, pine, teak) can be classified as hydrophilic and teak is the most these three species. Oak and cedar are slightly hydrophobic. It is possible also to estimate the hydrophilic or hydrophobic character of the surfaces by components of interfacial tension. With increasing LW values, the apolarity of a surface increases, which results in lower affinity of that surface for polar liquids. A high AB component value means more water of hydration on the surface and increased hydrophilicity. According to these criteria, the pine wood is considered to hydrophilic because their AB values are higher than those of the other wood surfaces. This result agrees with those obtained by contact angle measurement with water ( w) that also classified as hydrophilic. 90 80 Hydrophobicity (°)

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70 60 50 40 30 20 10 0 Cedar

Beech

Pine

Ash

Oak

Teak

Wood species Figure 2. Water contact angle ( w) in function of the wood species. (Cedar [25], Beech [26], Pine [26], Ash [27], Oak [27], Teak [27]).

The component - can also be a semi-quantitative measure of hydrophobicity. - values ≤ 25.5 mJ/m2 indicate a hydrophobic surface regardless of the value of the apolar component. The - values between 25 mJ/m2 and 35 mJ/m2 suggest that the hydrophobicity is dependent upon the apolar component. Thus, except teak wood, all wood species (Oak, beech, pine, cedar, ash) are hydrophobic ( - values ≤ 25.5 mJ/m2) (Figure 3). These results are different from those determined by qualitative criteria using contact angles with water ( w), which considered beech, pine, teak hydrophilic.

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Also, the surfaces are hydrophilic when LW ≤ 45 mJ/m2 and hydrophobic when LW ≥ 46 mJ/m2 [28]. According to these criteria, beech and pine wood can be considered hydrophobic ( LW ≥ 46 mJ/m2) while oak, teak, ash and cedar hydrophilic ( LW ≤ 45 mJ/m2) (Figure 4).

Electron donor proprieties (mJ m-2)

60 50 40 30 20 10 0 Cedar

Beech

Pine

Ash

Oak

Teak

Wood species

Lifshitz–van der waals components (mJ m-2)

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Figure 3. Electron donor proprieties ( -) in function of the wood species.

50 45 40 35 30 25 20 15 10 5 0 Cedar

Beech

Pine

Ash

Oak

Teak

Wood species

Figure 4. Lifshitz–van der Waals components (

LW

) in function of the wood species.

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Soumya El Abed, Saad koraichi Ibnsouda and Hassan Latrache

It is much more important therefore, to study and interpret the hydrophobicity into account the all surface tension components of wood surface. Accordingly, using the approach of Van Oss and co-workers [29-30], it is possible to determine the absolute degree of hydrophobicity of any substance (i) vis-a-vis water (w), which can be precisely expressed in applicable System International (Formula 1). ΔGiwi= - 2 ( W+ i- )1/2 ]

iw

= - 2[(

LW 1/2 i

)

-(

LW 1/2 2 w

)

) + 2((

+ i

- 1/2 i )

+(

+ W

- 1/2 W

)

-(

+ - 1/2 i w )

-

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If the interaction between the two entities is stronger than the interaction of each entity with water, the material is considered hydrophobic (ΔGiwi < 0); conversely, for a hydrophilic material, ΔGiwi >0. Taking into account the values of ΔGiwi, all the wood species are hydrophobic (ΔGiwi < 0) (Figure 5).

Figure 5. Free energy of interaction (ΔGiwi) in function of the wood species.

In summary, the hydrophobicity of oak wood and other wood species reported here was completely different on the different criteria or approach used to classify the hydrophobicity proprieties. However, the utilization the approach of van oss and co-workers [29-30], seems to be more significant to interpret hydrophobicity parameters, while the other criteria are whether qualitative or semi-quantitative.

2.2. Wood Lifshitz–Van Der Waals and the Acid–Base Components The initial step in microbial adhesion is mainly governed by an interplay of Lifshitz-van der Waals, electrostatic, and Lewis acid–base interactions between the microbial surface and Oak: Ecology, Types and Management : Ecology, Types and Management, Nova Science Publishers, Incorporated, 2012. ProQuest Ebook Central,

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the solid material [29, 31-33] and several authors have reported that that acid–base interactions were an important factor in mediating cell adherence to a wide variety of surfaces [34-36]. The Lifshitz–van der Waals (γLW) and acid–base (γAB) surface tension components were calculated from the contact angle of a drop of water or another liquid on a given surface or on a closed layer of surface. The contact angle of a drop of liquid on a solid surface is a function of the three different surface free energies involved and may be quantified in terms of the three surface tensions (y, expressed in (N m-1) through Young's equation: γL (Cosθ +1) = 2 [(γS LWγ LLW)1/2 + (γS+ γ L-)1/2 + (γS- γ L+ )1/2 ] where θ is the measured contact angle, γLW is the Van der Waals free energy component, γ+ is the electron acceptor component, γ− is the electron donor component and the subscripts (S) and (L) denote solid surface and liquid phases respectively. The surface free energy is expressed as:

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γS = γ SLW+ γS AB where SAB = 2( S- . S+)1/2 is the acid-base free energy component. Comparison of the surface properties of the different wood species, Figure.6. showed that the that the electron donor of oak and beech wood were low that all species. Figure.6. show also that teak and pine wood exhibits more electron donating ( - = 59.3 mJ.m-2) and ( - = 24.2 mJ.m-2) respectively. Teak wood is slightly electron donor because the - values are higher than the + values. Conversely, the beech and oak are more electron accepting because the + values are higher than the -. On the other hand, contact angles and surface free energies measured on different wood species indicate that hydrophilic character of the surface associated with low contact angle is strongly correlated with high values of electron-donating component, while hydrophobic character is correlated with low values of electron-donating component.

- (mJ.m-2) + (mJ.m-2)

Figure 6. Electron donor acceptor proprieties in function of the wood species.

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Soumya El Abed, Saad koraichi Ibnsouda and Hassan Latrache

3. THEORETICAL PREDICTION OF MICROBIAL ADHESION ON WOOD SPECIES The patterns of degradation by fungi and bacteria have been well characterized [37]. White, brown and soft rot fungi cause distinct forms of decay that can be easily identified [37-38]. Recent work dealing with bacterial degradation of wood also has demonstrated that there are distinct forms of bacterial decay that are caused by different types of bacteria, and these decay types are distinguishable from fungal degradation patterns [39-41] What type of wood species studied and how microorganisms adhere on wood are important questions that need consideration if wooden cultural properties are to be studied. Thus, It is essential to improve our understanding of adhesion processes of woods and to have indications on adhesion potentials of microbiata onto wood species. Several works have evaluated the potentiality of adhesion in various surfaces using thermodynamic approach [35, 42-43]. We report here comparing potential adhesion on wood species, applying isolated bacteria and fungi in our laboratory [25]. The total free energy of interaction between microbial cell (M) and wood surface (S) through water (W) is calculated as the sum of the LW and AB interactions as proposed by Van Oss [26]. ΔGMLS Total = ΔGLW MLS + ΔGABMLS

Eq. (A.1)

where ∆GLW = ((

LW 1/2 M

)

-(

LW 1/2 2

) ) - ((

S

LW 1/2 M

)

-(

LW 1/2 2 L

) ) - ((

LW 1/2 S

)

-(

LW 1/2 2 L

) )

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Eq. (A.2) and ∆GAB = 2[( L +)1/2 [( – ( L+ S-)1/2 ]

- 1/2 C

)

+(

- 1/2 S

)

-(

- 1/2 L

) ]+(

-)1/2 L

[(

+ 1/2 C

)

+(

+ 1/2 S

)

-(

+ 1/2 S )

+ 1/2 L

) ] -( LEq. (A.3)

Microbial adhesion is favored if ΔGMLS Total is negative and unfavored if ΔGMLS Total is positive. On the one hand, the bacteria cells have a higher ability to adhere in wood species than fungal spores (Fig. 7a). Furthermore, for all spore fungi, it can be seen that the positive values of the ΔGTotal indicate unfavorable adhesion to some wood species like teak, pine and cedar , from a thermodynamical point of view. On the opposite, we can see that the bacterial adhesion was dependent on bacteria studied on those surfaces. For other types of wood (oak, beech, ash), a large variation can be observed. For example, adhesion process of the Klebsiella sp. (SS4) is unfavorable to beech. In contrast, the same strains show favorable adhesion to oak and beech [25]. Also, only of Penicillium commune (SS10) and Penicillium chrysogenum (SS11) spores, it must be noted that the adhesion process is not thermodynamically favorable to any of the wood species studied (ΔGTotal > 0) [25].

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(a)

227

(b)

Figure 7. (a). Percentage of theoretical adhesion of all microorganisms in all wood species. (b). Potentiality of adhesion on some wood species [25].

Interestingly, it should be expected that teak exhibit a better proprieties than the others studied to use in construction and also in building historic monuments because the results show unfavorable adhesion in all microorganism tested. In terms of thermodynamic adhesion potential, we can classify wood species as follows (Figure.7b): oak > beech > ask > cedar > pine > teak.

REFERENCES

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Krummbein,W.E. Diakumaku, E. Gehrmann, C. Gorbushina, A. Grore, G. Heyn, C. Kuroczin, J. Schoschtak, V. Sterflinger, K.Warscheid, T.Wolf, B. Wollenzien, U. YunKyung, Y. &Petersen, K. (1996). Chemiorganotroph microorganisms as agents in the destruction of objects of art: a summary. In: Reiderer, J. (Ed.), Proceedings of the Eighth International Congress on Deterioration and Conservation of Stone, vol. II. Berlin, pp. 631–636. Kemmling, A. Kämpfer, M. Flies, C. Schieweck, O. & Hoppert, M. (2004). Biofilms and extracellular matrices on geomaterials. Environmental Geology, vol.46, pp.429– 435. Gorbushina, A.A. Heyrman, J. Domieden, T. Gonzales-Delvalle, M. Krumbein,W.E. Laiz, L. Petersen, K. Saiz-Jimenez, C. & Swings, J. (2004). Bacterial and fungal diversity and biodeterioration problems in mural painting environments of St. Martins church (Greene-Kreiensen, Germany). Internationnal Biodeterioration and Biodegradation, vol.53, pp.13–24. Görs, S. Schuhmann, R. Häubner, N. & Karsten, U. (2007). Fungal and algal biomass in biofilms on artificial surfaces quantified by ergosterol and chlorophyll a as biomarkers. Internationnal Biodeterioration and Biodegradation, vol. 60, pp.50–59. Geoffrey, D. (2003). Microview of wood under degradation by bacteria and fungi. Wood Deterioration and Preservation. ACS Symposium Series, vol. 845, pp 34–72. Burnes, T.A. Blanchette, R.A. Farrell, R.L. (2000). Bacterial Biodegradation of Extractives and Patterns of Bordered Pit Membrane Attack in Pine Wood. Applied Environmental Microbiology, vol.66, pp.5201–5205.

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Soumya El Abed, Saad koraichi Ibnsouda and Hassan Latrache Blanchette, R.A. Nilsson, T. Geoffrey, D. & André, A. (1989). Biological degradation of wood. Archaeological Wood. Advances in Chemistry, vol. 225, pp.141–174. Blanchette, R.A. (2000).A review of microbial deterioration found in archaeological wood from different environments. International Biodeterioration & Biodegradation, vol.46, pp.189-204. Bos, R., van der Mei, H.C. & Busscher, H.J. (1999). Physico-chemistry of initial microbial adhesive interactions - its mechanisms and methods for study. FEMS Microbiology Reviews, vol.23, pp.179-230. Bryers, J.D.E. (2000) Biofilms II: Process Analysis and Applications, 432 pp. WileyLiss. Walinder, M.E.P. & Johansson, I. (2001). Measurement of wood wettability by the wilhelmy method, part 1. Holzforschung, vol. 55, pp.21–32 Gindl, M. Sinn, G. Gindl, W. Reiterer A. & Tschegg, S. (2001). A comparison of different methods to calculate the surface free energy of wood using contact angle measurements. Colloids and surfaces A: Physicochemical and Engineering Aspects, vol. 181, pp. 279–287. Chibowski, E. & Perea-Carpio, R. (2002). Problems of contact angle and solid surface free energy determination. Advances in Colloid and Interface Science, vol. 98, pp.245– 264. Zenkiewicz, M. (2007). Comparative study on the surface free energy of a solid calculated with different methods, Polymer Testing, vol.26, pp.14-19. Kalnins, M.A. Katzenberger, C. Schmieding, S.A. & Brooks, J. K. (1988). Contact angle measurement on wood using videotape technique. Journal of Colloid and Interface Science. vol. 125, pp.344-346. Gardner, D. J. Generalla, N.C. Gunnels, D.W. & Wolcott, M.P. (1991). Dynamic wettability of wood. Langmuir, vol. 7, pp. 2498–2502. Boehme, C. & Hora, G. Water (1996).Absorption and contact angle measurement of native european, north american and tropical wood species to predict gluing properties. Holzforschung vol. 50, pp.269-276. Shen, Q. Nylund, J. & Rosenholm, J.B. (1998). Estimation of the surface energy and acid-Base properties of wood by means of wetting method. Holzforschung, vol. 52, 521-529. de Meijer, M. Haemers, S. Cobben W. & Militz, H. (2000). Langmuir, vol.16, pp.93529357. Magnusson, K.E. (1982). Hydrophobic interaction: a mechanism of bacterial binding. Scandinavian Journal of Infectious Diseases (suppl) vol.33, pp.32–36. Rosenberg, M. & Kjellerberg, S. (1986). Hydrophobic interactions: role in bacterial adhesion. Advances in Microbial Ecology, vol.9, pp.353–393. Absolom, D.R. Lamberti, F.V. Policova, Z. Zingg, W. Van Oss, C.J. & Neumann, A.W. (1983). Surface thermodynamics of bacterial adhesion. Applied and Environmental Microbiology, vol.46, pp.90–97. Vogler, E.A. (1998). Structure and reactivity of water at biomaterial surfaces. Advances in Colloid and Interface Science, vol. 74, pp. 69–117. Oliveira, R. Azeredo, J. Teixeira, P. & Fonseca, A.P. The role of hydrophobicity in bacterial adhesion. In: Gilbert, P., Allison, D., Brading, M., Verran, J., Walker, J.

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[41] Singh.. A. P. & Butcher, J. A. (1990). Bacterial degradation of wood cell wall: A review of degradation patterns. International Research Group on Wood Preeservation. Document I RG/WP/1460. [42] Sharma, P.K. & Hanumantha, R.K. (2003). Adhesion of Paenibacillus polymyxa on chalcopyrite and pyrite: surface thermodynamics and extended DLVO theory, Colloids and Surfaces B: Biointerfaces, vol. 29, pp. 21-38. [43] Hailiang, D. Onstott, T.C. Ko, C-H. Hollingsworth, A.D. Brown, D.G. & Mailloux, B.J. (2002) Theoretical prediction of collision efficiency between adhesion-deficient bacteria and sediment grain surface. Colloids and Surfaces B: Biointerfaces, vol. 24, pp. 229–245.

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INDEX # 20th century, ix, 9, 39, 173 21st century, 106

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A abiotic parameter, 4 access, 25, 41, 43, 44, 217 accessibility, 32 acetaldehyde, 70 acid, 20, 72, 80, 87, 93, 96, 177, 183, 188, 191, 197, 204, 205, 221, 224, 225, 228 acidic, 68, 199 acidity, 60, 68 activase, 201 AD, 205 adaptability, 195 adaptation(s), 41, 87, 104, 152, 195, 202 adhesion, vii, x, 219, 220, 221, 224, 226, 227, 228, 229, 230 adhesive interaction, 228 adjustment, 94, 95, 97, 201 adsorption, 71, 84, 220 advancement, 5 aesthetic(s), 1, 11, 13, 20, 25, 44, 45, 46, 47, 49, 88, 128, 137, 139, 140, 141, 146, 148 Africa, 90 age, vii, 9, 11, 15, 16, 17, 20, 22, 24, 26, 27, 28, 30, 31, 32, 37, 40, 46, 59, 60, 61, 69, 80, 108, 109, 120, 153, 154, 155, 156, 158, 179, 181, 182 agencies, 48 aggregation, 220 aggression, 36 aging process, 60, 61, 68, 71, 81, 197 agriculture, 6, 8, 39, 41, 42, 152 air quality, 3 air temperature, 162

alcohols, 66, 68, 69 aldehydes, 65, 66, 67, 68, 74, 81, 183, 185 aldolase, 201 Algeria, 88, 194, 205 aliphatic compounds, 178 almonds, 66, 187 alternative quality, 73 alters, 214 aluminium, 165 AME, 127 amplitude, 154 amylase, 201 anatomy, 19, 113, 130, 137, 203 ancestors, 45 anchoring, 220 anisotropy, 128 anthocyanin, 71, 82 aptitude, 175 Arabidopsis thaliana, 205 aromatic compounds, 20, 123, 146, 179, 180 Asia, 6, 173 assessment, 46, 94, 127, 129, 139, 163 assimilation, 95 astringent, 183 asymmetry, 206 atmosphere, 3, 163, 164, 185 ATP, 200, 201 attachment, 220 attribution, 143 authorities, 8 avian, 53 awareness, 6, 9, 47, 48, 120

B bacteria, 72, 77, 143, 187, 189, 220, 226, 227, 229, 230 bacterial cells, 220

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Index

Balkans, 174 ban, 153 barrel aging period, vii, 59 barriers, 41 base, 22, 28, 90, 92, 115, 168, 221, 224, 225 beams, 125, 138 beer, 82 behaviors, 47, 222 Belgium, 56 bending, 126, 127, 128, 146 beneficial effect, 108 benefits, ix, 5, 21, 28, 36, 43, 48, 49, 106, 110, 173, 209 beverages, 81 biodiversity, vii, 1, 2, 3, 4, 5, 11, 13, 25, 32, 36, 37, 38, 47, 48, 49, 52, 106, 107, 152, 195, 213 biological processes, ix, 193 biological systems, 198, 221 biomarkers, 227 biomass, 28, 29, 31, 34, 35, 42, 50, 104, 105, 108, 111, 158, 168, 212, 227 biotic, 4, 195 birds, 4, 37, 38, 39, 40, 50, 51, 97, 114, 196 bleaching, 70 blends, 179 Bolivia, 171 bonding, 148 bonds, 71 BOS, 202 branching, 14, 22 brass, 165 breakdown, 165 breaking force, 126 breeding, 22, 50, 51, 52, 169, 195 browsing, 112 Bulgaria, 57 buns, ix, 173, 185 Butcher, 230 buyers, 137 by-products, 161, 185, 186, 188

C campaigns, 9 candidates, 200 carbohydrate(s), 19, 34, 123, 201, 202 carbohydrate metabolism, 201 carbon, 3, 5, 19, 36, 48, 49, 93, 95, 104, 106, 119, 123, 158, 218 case study, 168 category b, 147 cattle, viii, 33, 36, 87, 112, 195 CCA, 169

cell membranes, 63 cellulose, 63, 78, 123, 177, 185, 187 certificate, 48 certification, 47, 48, 49, 52 challenges, ix, 47, 193, 195 chemical(s), vii, viii, 20, 21, 36, 59, 60, 63, 65, 66, 68, 69, 70, 73, 79, 104, 112, 119, 120, 122, 123, 137, 138, 140, 145, 146, 177, 178, 179, 180, 182, 183, 184, 185, 188, 191, 196, 197, 198, 201, 202, 203, 220 chemical characteristics, 20, 146 chemical interaction, 220 chemical properties, 104, 185 chemical reactions, 177 chemical structures, 66 children, 220 Chile, 89 chimneys, 132 chlorophyll, 201, 227 chloroplast, 203, 204 chromatography, 178 circulation, 130, 131, 183 cladding, 148, 168 classes, 10, 12, 13, 21, 24, 26, 29, 31, 51, 139, 143, 144, 145 classification, viii, 10, 22, 45, 63, 71, 119, 137, 138, 139, 140, 141, 142, 143, 144, 163, 175 cleaning, 10, 14, 25, 42, 188, 189 cleanup, 131 cleavage, 80, 191 climate(s), 2, 3, 4, 6, 8, 13, 32, 36, 38, 41, 44, 47, 53, 88, 89, 97, 100, 101, 104, 105, 111, 116, 123, 124, 147, 168, 175, 195, 202, 206, 213, 215, 216, 217 climate change, 6, 47, 53, 88, 97, 101, 104, 105, 213, 215, 216, 217 climatic factors, 64, 101 closure, 95, 96, 97, 101 clustering, 200 CO2, 101, 117 coal, 88 coastal region, 89 coatings, 167 codominant, 10, 14, 15, 206 coffee, ix, 81, 173, 186, 187, 189 collaboration, 208 colonisation, 203 colonization, 212, 216 color, ix, 45, 61, 69, 70, 71, 74, 75, 77, 80, 82, 83, 120, 121, 139, 140, 143, 146, 151, 190 combustibility, 4 commerce, 8 commercial, 5, 21, 32, 112, 161, 165, 167

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Index common agricultural policy, 114 community(s), 4, 5, 36, 40, 41, 194, 208, 209, 213, 214, 215, 216, 217, 218 compaction, 35, 46 compatibility, 43 competition, 9, 10, 13, 14, 15, 16, 24, 38, 76, 100, 106, 117 competitors, 14, 15 complement, 61, 198 complexity, vii, 1, 38, 40, 59, 61, 66, 71, 88, 186, 198, 212 composites, ix, 151, 164, 167, 169 composition, vii, 2, 4, 11, 21, 36, 37, 38, 40, 44, 45, 59, 60, 61, 62, 63, 65, 66, 68, 74, 78, 79, 80, 81, 82, 83, 84, 85, 86, 110, 123, 138, 140, 180, 182, 183, 184, 189, 190, 191, 196, 197, 201, 202, 203, 205, 212, 213 compounds, vii, ix, 4, 20, 59, 60, 61, 63, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 77, 78, 79, 80, 81, 82, 85, 86, 146, 148, 173, 176, 177, 178, 179, 180, 184, 185, 186, 187, 188, 189, 191, 197, 204 compression, 126, 127, 142, 143, 152 computer, 28, 52, 158, 159, 170 computer simulations, 158 condensation, 69, 70, 77 conditioning, 220, 221 conduction, 73 conductivity, 95, 96, 97, 101 conference, 52 configuration, 162 conflict, 43 conformity, 141 confrontation, 45 Congress, 113, 227 conifer, 120 conservation, vii, viii, ix, 1, 2, 3, 4, 5, 8, 9, 11, 12, 13, 25, 32, 36, 37, 38, 39, 40, 42, 44, 45, 47, 48, 49, 51, 76, 77, 87, 88, 93, 97, 107, 114, 128, 193 conserving, 2, 195 consolidation, 123 constituents, 123 construction, ix, 2, 6, 8, 9, 21, 42, 95, 119, 137, 138, 140, 146, 148, 151, 153, 170, 227 consumers, 21, 47, 48, 49, 61, 72, 76 consumption, 8, 9, 23, 34, 35, 38, 40, 97, 111, 132, 188 contact time, vii, 59, 66, 74, 75, 86 containers, ix, 60, 137, 146, 173, 188, 189 contaminant, 72, 73 contamination, 72, 143, 179, 188, 189 contour, 121 controversial, 42, 108 Convention on Biological Diversity, 3

cooling, 8 correlation(s), 23, 96, 171, 196 corrosion, 123, 135 cortex, 209 cost, viii, 60, 61, 73, 107, 132, 176 Costa Rica, 54 costs of production, 145 cotyledon, 202 counseling, 167 covering, 13, 36, 88, 168, 194, 196 cracks, viii, 17, 20, 119, 125, 126, 130, 133, 137, 142, 143, 144 craving, 146 Croatia, 39 crop(s), viii, 9, 12, 13, 14, 15, 16, 20, 22, 25, 41, 50, 52, 62, 87, 97, 110, 111, 112, 196 crown(s), 10, 15, 17, 20, 22, 23, 28, 29, 30, 31, 34, 36, 39, 45, 46, 98, 99, 100, 104, 108, 200 CT, 15, 57, 170 cultivars, 83, 206 cultivation, 34, 203 cultural heritage, 48 cultural practices, 2, 32 cultural values, 3, 43, 49 culture, 21, 43, 203 customers, 179 CV, 157, 171 cycles, 16, 24, 48, 101 cycling, 105, 115, 209 Cyprus, 54

D damages, 13, 43 danger, 142, 152 data analysis, 205, 208 data set, 116 database, 208, 215 decay, 23, 46, 122, 140, 226 defects, 2, 15, 17, 19, 20, 21, 22, 41, 128, 131, 132, 133, 136, 137, 138, 141, 142, 146, 153, 159, 161 deficit, 94, 97, 202 deforestation, 6, 39 deformation, 20, 127, 129, 130, 135, 142, 164, 165 degradation, 3, 25, 38, 39, 42, 48, 60, 65, 70, 77, 80, 106, 123, 125, 138, 140, 143, 144, 158, 190, 220, 221, 226, 227, 228, 229, 230 dehydration, 64, 201 Dekkera bruxellensis, 72, 84, 85 Denmark, 56 density values, ix, 124, 151, 154 deposition, 93, 213 deposition rate, 213

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Index

depreciation, 132 depression, 185, 211 depth, 92, 93, 94, 142, 184 derivatives, 72, 74 desiccation, 13, 198 destruction, 3, 4, 6, 9, 40, 227 detachment, 220 detection, 80 devaluation, 140 deviation, 129, 139, 140, 159, 162 diet, 6, 34, 35, 97, 110, 197 diffusion, 60, 75, 185, 189 digestibility, 33, 34 digestion, 199 discontinuity, 35, 140 discrimination, 200 diseases, 41, 97, 108, 195 displacement, 158 distortions, 132, 133 distribution, 6, 11, 12, 13, 15, 16, 23, 28, 29, 31, 37, 94, 101, 109, 121, 142, 154, 161, 180, 182, 195, 216, 229 diversification, vii, viii, 43, 106, 151, 152, 153 diversity, 2, 3, 4, 32, 37, 38, 40, 43, 44, 45, 47, 88, 104, 112, 114, 195, 204, 206, 212, 213, 214, 218, 227 DNA, 196, 203, 204, 208, 210 DNA sequencing, 208, 210 DOC, 76 DOI, 202 domestication, 6 dominance, 17, 214 draught, 111 drought, x, 6, 13, 37, 47, 89, 90, 93, 94, 95, 97, 100, 101, 112, 113, 116, 117, 152, 194, 195, 196, 201, 202, 203, 204, 206, 211, 214, 217 dry matter, 35, 63, 99, 177 drying, viii, 2, 63, 73, 79, 103, 119, 124, 125, 126, 128, 130, 131, 132, 133, 134, 135, 139, 140, 141, 142, 143, 144, 149, 169, 177, 183, 217 durability, viii, 5, 19, 21, 49, 119, 120, 123, 124, 137, 139, 141, 142, 144, 145, 146, 152

E Eastern Europe, 62 ecological processes, 40 ecological requirements, 42 ecology, vii, 97, 203, 216, 218 economic losses, 72 economics, 97 ecosystem, vii, 1, 2, 4, 21, 32, 37, 38, 40, 47, 49, 50, 94, 97, 152, 216

ecosystem restoration, 47 edible mushroom, 5, 32, 46 editors, 81 education, 43, 44 elaboration, 61 electric current, 73, 85 electricity, 73, 132 electrodes, 143 electron, x, 219, 221, 225 electron donor-acceptor, x, 219 electrophoresis, 205, 206 e-mail, 193 embolism, 101 emission, 23, 115 employment, 61, 73 encouragement, 48 endangered, 37 endangered species, 37 energy, 8, 51, 101, 104, 119, 127, 136, 145, 198, 215, 221, 224 engineering, 220 England, 22, 53, 55, 56 environment(s), vii, viii, x, 1, 2, 3, 4, 5, 6, 13, 18, 21, 23, 36, 37, 38, 39, 40, 42, 44, 46, 47, 48, 49, 84, 87, 93, 106, 125, 131, 147,158, 188, 196, 206, 213, 219, 220, 227, 228 environmental conditions, 12, 37, 60, 61, 194, 195, 198 environmental protection, 5 enzyme(s), 72, 196, 199, 201 EPS, 220 equilibrium, 68, 125, 132, 162 equipment, 132, 199, 220 erosion, 3, 6, 13, 37, 41, 48, 94, 104, 107, 148, 229 ester, 68 ethanol, 72, 177, 188 ethers, 80 ethylene, 96 eucalyptus, 9 Europe, 3, 5, 6, 47, 62, 114, 117, 145, 152, 173, 174 European policy, 5 European Union, 88 evaporation, 3, 41, 61, 130, 185 evapotranspiration, 100, 103 evidence, 53, 108, 203, 209, 217 evolution, 6, 7, 28, 29, 68, 71, 77, 78, 79, 81, 93, 94, 97, 112, 132, 148, 183 exchange rate, 95 exclusion, 11, 116 execution, 14, 48 experimental design, 198, 205 expertise, 199 exploitation, 111, 140, 152, 158

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Index exposure, 148, 153, 162, 164, 206 external influences, 46 extinction, 4, 38 extraction, vii, 59, 61, 66, 68, 69, 74, 81, 153, 157, 158, 187, 189, 198, 205 extracts, 79, 190, 191, 200

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F Fabrication, 79 families, 83, 186 farmland, 7 fat, 71, 197, 198, 205 fatty acids, 63, 64, 74, 178, 197, 204 fauna, 3, 4, 40, 98 feces, 212 feelings, 6 fencing, 45, 109, 145, 148 fermentation, 74, 76, 80, 85, 187, 188, 189 fertility, 25, 31, 47 fertilization, 32, 113 fertilizers, 109 fiber(s), 34, 121, 122, 123, 124, 125, 126, 130, 133, 135, 139, 140, 143, 162, 163 financial, 15, 108 Finland, 116, 159, 204 fires, 4, 11, 38, 39, 48, 101 fishing, 8 fitness, 63, 167 fixation, 148 flame, 73 flavonoids, 69 flavor, 66, 67, 72, 74, 75, 78, 79, 82 flavour, 69, 85, 178, 189, 191 flaws, 142 flight, 206 flooding, 39, 48 floods, 101 flooring, ix, 9, 15, 119, 127, 130, 138, 140, 144, 145, 147, 151, 152, 153, 159, 161, 162, 163, 164, 165, 166, 167, 168, 169 flora, 3, 4, 37, 40, 43, 48, 88, 101 flora and fauna, 37, 40, 43, 48, 88 flour, 169, 198 flowers, 104, 105 fluctuations, 101 fluorescence, 201 food, 33, 34, 38, 39, 97, 109, 110, 112, 188, 213 force, 164 forest ecosystem, 4, 48, 97, 105, 115, 117, 168, 217 forest fire, 3, 4, 25, 47 forest formations, 6, 47

forest management, vii, 1, 5, 9, 32, 37, 43, 44, 47, 48, 49, 97, 105, 114, 120 forest resources, 8, 48, 49, 170 forest restoration, 42 formaldehyde, 148, 168 formation, viii, x, 6, 14, 16, 17, 19, 42, 51, 60, 65, 70, 72, 75, 81, 82, 93, 131, 137, 149, 158, 162, 184, 185, 207, 213, 220 formula, 154 fractures, 22 fragments, 38, 73, 74, 75, 90, 93 France, 25, 50, 51, 53, 54, 55, 56, 62, 77, 82, 83, 88, 153, 167, 168, 173, 176, 181, 182, 184, 194, 202, 204 free energy, 221, 225, 226, 228, 229 frequency distribution, 11 friction, ix, 151 frost, 13, 97, 138, 140 fructose, 123, 201 fruits, ix, 38, 193, 196 functional architecture, 46 funding, 167 fungi, vii, x, 4, 32, 39, 49, 72, 88, 104, 107, 140, 142, 143, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 220, 226, 227 fungus, 88, 138, 211, 218

G gel, 198, 205, 206 genes, 208, 218 genetic diversity, 40, 195, 202 genetic engineering, 203 genetic information, 198 genetics, 18, 19, 24, 25, 137, 206 genome, 198, 206 genotype, 206 genus, viii, 6, 62, 73, 87, 88, 111, 196, 206 geographical origin, 62, 77, 175, 179, 180 geometry, 128, 132, 141 Germany, 51, 57, 214, 227 germination, 12, 198, 212 global climate change, 101, 214 global warming, x, 195, 207, 213 glucose, 123 glucoside, 188 glue, 148 glutamine, 201 glycolysis, 202 good behavior, 145 goods and services, vii, 1, 23, 32, 48, 49 governments, 8 grades, 22, 137, 138, 140, 141, 144

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grading, viii, 22, 119, 137, 141, 143 grain size, 125 graph, 131 grass(s), 5, 33, 34, 36, 93, 97, 106, 107, 110, 111 grasslands, 110, 111, 195 grazing, 5, 6, 7, 25, 32, 33, 34, 36, 40, 41, 42, 46, 106, 109, 110, 111 greenhouse, 3 groundwater, 217 group variance, 157 growth models, 26 growth rate, 21, 46, 95, 102, 103, 158, 171 growth rings, 15, 20, 62, 120, 121, 124, 139 guidelines, 5, 47, 48, 107

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H habitat quality, 38 habitat(s), 2, 4, 36, 37, 38, 40, 41, 45, 53, 88, 104, 209, 213, 214 halogens, 179 hardness, ix, 19, 126, 128, 134, 146, 151, 162, 164, 165, 166, 177, 189 hardwood forest, 6, 51, 216 hardwoods, 123, 141, 157, 171 harvesting, 2, 11, 13, 14, 16, 17, 24, 26, 44, 140 HDPE, 169 HE, 215, 217 healing, 18, 19 health, 40, 43, 45, 48, 49, 100, 107, 143, 220 health condition, 43 health risks, 220 health status, 143 heavy metals, 213 height, 9, 10, 11, 14, 15, 17, 18, 19, 21, 22, 23, 24, 26, 27, 28, 29, 30, 31, 34, 39, 41, 58, 108, 153, 170, 180, 196, 201 height growth, 9, 23, 28 hemicellulose, 63 hemisphere, 88 heritability, 169 heterogeneity, 121, 154, 155, 157, 167 high fat, 197 historical overview, 113 historical reason, 45 history, 7, 8, 21, 23, 45, 97, 99, 116, 117, 203, 204 Holocene, 53 homogeneity, 139, 158, 167 horses, 33, 36 host, 209, 211, 217 human, viii, 2, 3, 4, 6, 37, 41, 42, 44, 48, 53, 69, 87, 88 human actions, 48

human activity, 4, 6, 37, 41, 42 human health, 69 humidity, 64, 65, 125, 132, 135, 162, 163, 164, 167, 183, 185 humus, 37 Hungary, 62, 84, 174 hunting, 5, 8, 32, 37, 43, 46, 88 husbandry, 36 hybrid, 198 hybridization, 198, 205 hydrogen, 123 hydrolysis, 177, 179, 183, 187, 188 hydrophilicity, 222 hydrophobicity, x, 219, 221, 222, 224, 228, 229 hydroxyapatite, 229 hydroxyl, 69 hygiene, 61, 188, 189 hypothesis, 198

I ideal, 20, 146, 176 identification, 45, 77, 121, 154, 159, 160, 190, 198, 199, 201, 202, 205, 208, 209, 215, 216 identity, 117 IFN, 4, 51 image(s), 137, 153, 159, 160, 164, 170, 180 image analysis, 137, 159 improvements, 199 in vitro, 33, 196 incidence, 47, 65, 77, 128 income, 43, 88, 108 indentation, 164, 168 India, 204 indirect effect, 47 individual character, 43, 46 individual characteristics, 46 individuals, 22, 25, 102, 195, 200 Indonesia, 54 indoor joinery, ix, 151, 153 industrial processing, 129, 145 industrial transformation, ix, 151 industry(s), 47, 48, 62, 72, 84, 130, 137, 144, 145, 146, 152, 160, 171, 174 infection, 206, 213, 215 infrared spectroscopy, ix, 193, 198 infrastructure, 109, 220 ingredients, 189 inhibition, 202 initial state, 188 initiation, 11 inoculation, 212 inoculum, x, 207, 209, 212, 213, 214, 216

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Index insects, 4, 18, 37, 38, 39, 40, 88, 97, 138, 140, 142, 143, 145, 196, 209 insulation, 5, 148, 177 integration, 170 integrity, vii, 1, 42, 49 intensity values, 201 intensive farming, 90 interdependence, 209 interface, 50, 185, 190 intervention, viii, 14, 26, 41, 45, 46, 87 invertebrates, 39 investment, 109 ionization, 206 ions, 83 Ireland, 56 iron, 213 irradiation, 73 irrigation, 130 islands, 51 isoflavone, 201 isolation, 14, 26, 195 isomerization, 64 isomers, 65, 66, 67, 74, 178 isozyme, 206 issues, vii, 1, 13, 44, 47, 49, 142, 152 Italy, 117, 174

lead, 11, 14, 19, 20, 32, 34, 38, 47, 48, 64, 69, 90, 107, 154, 197 leakage, 63, 163, 164 legs, 34 leisure, 2, 5, 43 life cycle, 195 lifetime, 3, 46, 108 Lifshitz–van der Waals components, x, 219, 223 light, 12, 13, 20, 37, 62, 65, 108, 146, 165, 166, 183, 212 light conditions, 37 lignin, 63, 65, 123, 176, 177, 179, 183, 185, 187 linoleic acid, 197 lipids, 63, 65, 199 liquid chromatography, 190 liquid phase, 225 liquids, 146, 177, 184, 222 Lithuania, 57 livestock, viii, 33, 34, 36, 40, 87, 88, 97, 98, 109, 110, 111, 112, 195, 196, 197 living conditions, 37 loci, 206 logging, 8, 39, 45 longevity, 6, 26, 43, 46 low temperatures, 95, 101, 103 lumen, 123 luminosity, 36

J

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M Japan, 55, 174 Java, 54 joints, 128

K ketones, 178, 183 kinetics, 75 knots, 14, 17, 18, 19, 21, 23, 129, 137, 138, 141, 142, 143, 144, 153, 159, 160, 170 Kyoto Protocol, 3

L labeling, 198 laboratory tests, 125 lactation, 112 lactic acid, 77 land abandonment, 144 landscape(s), 2, 5, 6, 11, 12, 25, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 51, 53, 90, 106, 107, 117, 203, 218 lateral roots, x, 207, 212

machinery, 2, 179, 199 macromolecules, 63, 176, 177, 184 magnesium, 213 magnitude, 83, 101 Maillard reaction, 65 majority, 69, 121, 156, 175, 177, 199 mammal(s), 4, 37, 38, 39, 97, 196, 212, 213, 214 man, viii, 3, 4, 6, 8, 36, 37, 43, 87, 111 manipulation, 117 manpower, 109, 136 mantle, x, 207 manufacturing, 9, 20, 146, 176, 183 mapping, 199, 206 market segment, 5 marketing, 5, 48, 137 marketing strategy, 137 Marx, 215 masking, 71 mass, 14, 34, 63, 99, 100, 105, 106, 112, 143, 163, 165, 166, 177, 190, 199, 202, 206, 213 mass loss, 163, 165, 166 mass spectrometry, 202, 206 masterpieces, 189

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238

Index

material surface, x, 219 materials, 3, 5, 90, 119, 123, 127, 148, 165, 221 matrix, 206, 220 matter, 34, 98, 99, 158 mature trees, x, 45, 153, 157, 161, 207, 211, 212, 213, 214 measurement(s), 96, 98, 103, 113, 134, 135, 142, 163, 221, 222, 228 meat, 97, 109, 111, 112, 195 mechanical properties, viii, ix, 19, 20, 49, 119, 124, 125, 146, 151, 153, 174, 177 mechanical stress, 123 media, 185 Mediterranean, viii, ix, 4, 6, 23, 32, 36, 87, 88, 89, 90, 93, 94, 97, 101, 104, 105, 108, 110, 112, 113, 114, 115, 116, 117, 152, 168, 193, 194, 195, 197, 198, 203, 204, 206, 214, 217, 218 Mediterranean climate, 87, 89, 90, 93, 101, 104, 105, 110, 113, 194, 214 medium composition, 70 medullary ray, 63 metabolic pathways, 201 metabolism, 187, 189, 201 metabolites, 199 metals, 70, 135 meter, 90, 160, 209 methodology, 50, 170 Mexico, 53, 54 mice, 195 microbial cells, 220 microorganism(s), viii, x, 59, 61, 64, 84, 219, 220, 226, 227 micro-oxygenation, vii, 59, 61, 69, 71, 74, 75, 82, 86 microscope, 134, 135, 164 microstructure, 135 Middle East, 88, 114 middle lamella, 122, 123 migration, 143 Miocene, 6 Missouri, 62 mixing, 104 modelling, 27, 159, 169, 170 models, 6, 28, 50, 53, 88, 105, 113, 159, 161, 169, 171, 221 modern society, 5 modifications, 61, 68, 73, 188, 198 modules, 161 modulus, 127 moisture, 64, 90, 93, 95, 110, 124, 125, 126, 131, 132, 133, 134, 135, 142, 146, 147, 148, 153, 162, 163, 169, 183 moisture content, 64, 110, 125, 126, 131, 132, 134, 142, 147, 148, 153, 162, 163, 169, 183

molecular weight, 70, 80, 123 molecules, 63, 70, 123, 178, 179, 186, 187, 188 monomers, 188 monosaccharide, 123 Morocco, 88, 194 morphology, 116, 198, 201, 203, 204, 210 mortality, 16, 28 mosaic, 34 mountain ranges, 89, 92 MR, 122, 205 mycelium, 212 mycorrhiza, x, 207, 213, 216 mycotoxins, 220

N national parks, 39 native species, 40, 48 natural appearance, 21 natural food, 112 natural habitats, 3, 212, 214 natural resource management, 3 natural resources, 4, 5 nature conservation, 52 near infrared spectroscopy, 201 negative effects, 97 Netherlands, 56 network theory, 218 neural network, 206 neutral, 20, 87, 211 nitrogen, 123, 201, 209, 214, 216 normal curve, 131 normal development, 14 normal distribution, 11 North Africa, 62, 152 North America, 62, 112, 145, 173, 174, 213, 214, 216, 221 Norway, 170 Norway spruce, 170 NPS, 39 null, 125 nutrient(s), x, 9, 24, 87, 90, 101, 104, 105, 110, 115, 117, 207, 211, 217 nutrition, 215

O oak forests, vii, 1, 2, 3, 4, 5, 6, 8, 9, 11, 15, 21, 23, 32, 33, 37, 38, 40, 42, 43, 44, 47, 49, 52, 97, 117, 128, 140, 152, 171, 194, 195, 196, 214 objective criteria, 141 oil, 93

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Index oleic acid, 197, 198 open spaces, 38 operating system, 166 operations, viii, 10, 16, 25, 28, 29, 40, 44, 65, 79, 128, 134, 136, 151, 152, 183, 185 opportunities, viii, 5, 38, 39, 43, 151, 152 optimization, 2, 5, 47, 49, 81, 137, 158 organ(s), 198, 200 organelles, 198 organic matter, 33, 93, 107, 110 organic polymers, 123 osmotic pressure, 211 overgrazing, 8, 48 oxidation, ix, 60, 61, 64, 69, 70, 76, 173, 183, 185, 188, 189, 191 oxygen, ix, 60, 61, 69, 75, 84, 123, 173, 185, 188, 201

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P Pacific, 216 parallel, 125, 126, 130, 139, 143, 163 parallelism, 128, 143 parasite, 205 parenchyma, 120, 121, 122, 133, 175 pasta, 51 pasture(s), 32, 36, 106, 107, 109, 110, 111, 112 PCR, 208, 216, 218 peace, 43 peptides, 199 perforation, 121, 122 periodicity, 4, 13, 16, 29 permeability, 3, 20, 124, 146, 177 permit, 71, 73 personality, 60 pests, 41, 48, 97, 101, 108, 198 pH, 68, 70, 187, 188, 229 pharmaceutical, 67, 187 phenol, 61, 67, 179, 198 phenolic compounds, 34, 60, 63, 69, 70, 74, 81, 83, 84 phenotypes, 21, 195 Philadelphia, 52 photosynthesis, 95, 104, 113, 201, 202, 206 phylum, 208, 209 physical and mechanical properties, 60, 63, 127, 137, 144, 148 physical environment, 32, 37 physical properties, 153, 176 Physiological, 94, 115, 206, 215 physiology, 113 pigs, viii, 33, 36, 87, 97, 112, 195, 197, 205

239

pith, 121, 129, 130, 138, 139, 144, 153, 154, 159, 167 plant growth, 101 plants, 4, 34, 36, 37, 38, 39, 40, 42, 45, 46, 94, 104, 199, 201, 206, 209, 211, 212, 216 plastic deformation, 143 plastics, x, 219 platform, 199 playing, 41, 95 Pliocene, 6 PM, 168 Poland, 57 polar, 222, 229 policy, 5, 8 policy instruments, 5 pollen, 7, 115, 200, 201, 203, 205, 217 pollination, 195 pollution, 44, 47, 101 polymer(s), 63, 73, 85, 123, 177, 184 polymerase, 208 polymerase chain reaction, 208 polymerization, 60, 69, 70, 71, 123 polymorphism(s), 196, 205, 208 polyphenolic compounds, vii, 59, 74 polyphenols, 20, 60, 64, 70, 83, 123, 146, 183, 188 polysaccharide(s), 63, 65, 71, 123, 199, 220 population, 12, 19, 25, 26, 72, 73, 84, 124, 195, 196, 198, 200, 203, 204, 206, 218 porosity, 20, 63, 69, 121, 146, 154 Portugal, ix, 1, 7, 36, 49, 50, 52, 53, 54, 56, 57, 88, 128, 151, 152, 153, 168, 169, 171, 194, 229 positive relationship, 98, 196 precipitation, 60, 61, 70, 87, 89, 90, 100, 101, 103, 110, 116, 198 predation, 38, 195, 203 predators, 38 preparation, 32, 128, 176, 196, 198, 199 preservation, 8, 48, 106 prevention, 2, 72, 106 principles, 38, 43, 47, 49, 51, 52, 170 producers, 49, 108, 137 production targets, 15 productive capacity, 2, 32, 48 professionals, 27 profit, 144 profitability, 5, 120, 129 project, 128, 167, 170 proliferation, 111 propagation, 4, 35 proposition, 200 protection, 1, 3, 8, 12, 13, 25, 32, 35, 36, 37, 38, 40, 41, 42, 43, 46, 47, 48, 49, 94, 107, 148, 188, 213, 220

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Index

proteins, 188, 198, 199, 200, 201, 202, 205, 206, 220 proteome, 196, 198, 200, 202, 205, 206 proteomics, 196, 198, 202, 205 pruning, 14, 17, 18, 19, 21, 34, 42, 46, 100, 105, 107, 108, 109, 110, 112, 113 public interest, 45 pulp, 69, 197 purification, 198 PVA, 148 PVAc, 146 pyrite, 230

Q quality control, viii, 119, 120 quality production, 136 quantification, 189, 196 quartz, 92 Queensland, 53

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R radiation, 21, 36, 100, 137, 149, 153, 170 radius, 158, 159 rainfall, 36, 69, 90, 91, 95, 103, 104, 105, 116, 131, 194, 204, 217 rangeland, 107 raw materials, 73 RE, 171 reactions, 61, 68, 69, 70, 77, 83 reactivity, 228 reading, 162, 163 reallocation of resources, 106 recalcitrant species, ix, 193 recognition, 10, 37, 43, 46, 141 recommendations, 147 reconciliation, 132 reconditioning, 135, 136 reconstruction, 40, 159, 160, 170 recovery, 5, 9, 36, 38, 40, 49, 95, 97, 127, 169, 202 recreation, 1, 2, 5, 9, 12, 25, 42, 43, 44, 45, 46, 49 recreational, 3, 32, 41, 43, 44, 45 recreational areas, 45 red wine, vii, ix, 59, 67, 71, 74, 75, 76, 77, 78, 80, 81, 82, 83, 84, 85, 86, 173, 186, 188, 190, 191 regenerate, 11, 195, 214 regeneration, 2, 9, 10, 11, 12, 13, 14, 16, 26, 38, 40, 41, 42, 44, 45, 48, 88, 97, 98, 104, 107, 108, 109, 111, 112, 195, 196, 203, 212, 213, 216 regional economies, 2 regression, 46 regulations, ix, 8, 32, 49, 151

rehabilitation, 42 relevance, ix, 8, 48, 49, 120, 193, 211 requirements, 5, 12, 13, 19, 20, 33, 48, 73, 112, 120, 136, 137, 141, 143, 168 researchers, 100, 185, 199 reserves, 34, 40, 95, 99, 123, 139, 202 residues, 145 resilience, 4, 127 resins, 4, 123, 168 resistance, ix, 8, 21, 25, 46, 48, 60, 115, 117, 120, 122, 123, 126, 127, 137, 148, 151, 152, 165, 166, 168, 177, 211 resolution, 73 resorcinol, 148 resources, 2, 5, 8, 23, 27, 32, 35, 42, 47, 104, 114, 115 response, 14, 16, 21, 24, 36, 94, 95, 101, 116, 158, 196, 201, 202, 206, 209, 212, 214, 215, 217 response capacity, 158 responsiveness, 217 restoration, 8, 9, 107, 195, 203, 212, 213, 214, 215 restoration plantings, 213 restoration programs, 195 restriction fragment length polymorphis, 215 restrictions, 167, 199 revenue, vii, 1, 17, 23, 169 reverse osmosis, 84 rhythm, 185 ribosomal RNA, 218 rings, 20, 62, 63, 101, 113, 120, 129, 130, 154, 156, 157, 158, 175 risk(s), 2, 14, 25, 35, 43, 61, 63, 101, 108, 142, 179, 183, 220 rodents, 39 Romania, 62 room temperature, 147 root(s), x, 23, 34, 46, 87, 120, 123, 197, 201, 207, 208, 209, 211, 212, 213, 214, 215, 216, 217, 218 root hair, x, 207 root system, 87, 197 rotations, 3, 24, 25, 31, 41 routes, 203, 209 royalty, 8 rubbers, x, 219 rules, 8, 130, 132, 137 Russia, 62, 174

S SAB, 225 safety, 44, 97 salts, 70, 123 saturation, 124, 125, 127, 130, 133, 162

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Index savannah, 194, 195 sawdust, 178, 183, 186, 189 scarcity, 99 science, 4, 76 scope, 47 Scots pine, 169 SDS-PAGE, 199, 200 sea level, 194 seasonal changes, 97, 101 seasonality, 36, 101, 104, 105, 168, 212 secondary metabolism, 82 secrete, 122 secretion, 123, 139 security, 43 sediment, 230 seed, 12, 13, 26, 40, 98, 196, 201, 204, 206, 214, 217 seedling(s), x, 12, 13, 17, 24, 36, 107, 109, 111, 112, 113, 116, 195, 196, 200, 201, 204, 206, 207, 209, 211, 212, 213, 214, 215, 216, 217, 218 senescence, 40, 46, 104 sensation(s), 71, 187, 188 sequencing, 202, 208, 218 services, 2, 5, 32, 46, 48, 49, 106 settlements, 6 shade, 13, 36, 217 shape, 12, 14, 17, 18, 41, 43, 44, 45, 65, 121, 125, 134, 136, 138, 140, 159, 170, 183 shear, 127 sheep, viii, 33, 36, 87, 111, 112 shelter, 36 shoot(s), 12, 14, 15, 21, 24, 25, 26, 34, 94, 104, 105, 139, 197, 211, 213, 214 showing, 4, 104, 126, 152, 157, 163, 167 shrubland, viii, 87 shrubs, 39, 107, 111, 213, 215 signals, 198 simulation(s), ix, 28, 151, 159, 161, 169, 170, 171 skin, 69, 188 SLA, 94, 95 social benefits, 32 social development, 3 society, 5, 6, 9, 47, 48, 49, 106 socio-economic needs, vii, 1, 49 software, 159, 161, 164, 169, 170, 171 softwoods, 125 soil erosion, 25, 39 solubility, 64 solution, 146 solvents, 177 South Africa, 89, 171 South America, 62 Southeast Asia, 62 sowing, 26, 106, 107, 111

241

SP, 99 Spain, v, viii, 36, 54, 55, 56, 57, 59, 62, 76, 77, 79, 82, 83, 84, 86, 87, 89, 90, 91, 92, 93, 94, 98, 99, 100, 102, 103, 104, 105, 106, 107, 109, 112, 113, 114, 115, 116, 117, 152, 170, 171, 174, 193, 194, 195, 196, 201, 203, 204, 205 species richness, 208, 218 specific gravity, 169, 171 specifications, 19, 137 spending, 136 spore, 226 Spring, 98, 175 sprouting, 14, 24, 105 stability, vii, viii, ix, 2, 5, 12, 17, 26, 32, 41, 43, 44, 45, 46, 48, 59, 60, 69, 70, 71, 76, 119, 146, 151, 162, 167, 168, 170, 204 stabilization, 69, 75, 85, 125, 135, 155, 158, 162 standard deviation, 98, 99, 100, 102, 103, 154 standard error, 105, 106 state, 32, 37, 45, 73, 125, 179, 186, 187, 188, 198 statistics, 156, 157, 170, 197 steel, ix, x, 74, 76, 86, 164, 173, 188, 219 sterile, x, 219, 220 steroids, 205 stock, 13, 31 stomata, 211 storage, 3, 49, 60, 61, 74, 80, 81, 82, 95, 143, 158, 189, 206 storms, 46 stress, x, 94, 95, 96, 97, 100, 101, 117, 125, 126, 194, 201, 202, 206 stress response, 206 stressors, 97 structural characteristics, 145 structure, ix, 2, 11, 12, 13, 21, 25, 26, 37, 38, 40, 41, 44, 45, 47, 49, 50, 52, 61, 63, 65, 71, 74, 120, 122, 123, 138, 140, 146, 149, 151, 159, 188, 194, 203, 212, 214, 218 style, 146 substitution, 104, 106 substrate, 72 succession, 11, 38 sulfur, 74 sulphur, 84, 189 surface area, 74, 108 surface energy, 221, 228, 229 surface layer, 131, 168 surface properties, 221, 225 surface tension, 224, 225 survival, 3, 4, 38, 44, 51, 93, 99, 197, 204, 214, 216 survivors, 46 susceptibility, 14

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Index

sustainability, vii, 1, 3, 4, 5, 32, 36, 37, 45, 47, 49, 106, 112 sustainable development, vii, 1, 5, 37, 47 sweat, 61, 72 Sweden, 56 swelling, 125, 139, 146, 162, 163, 164 Switzerland, 115 symbiosis, 214, 216, 218 synthesis, 65, 72, 84 Syria, 88, 194

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T tanks, 74, 75, 76, 86 tannins, 20, 60, 61, 63, 69, 70, 71, 123, 131, 144, 146, 176, 177, 178, 180, 188, 190 target, 13, 15, 16, 21, 24, 169 taxa, 198, 208, 211 technical support, 25 techniques, viii, ix, 2, 9, 20, 60, 61, 72, 73, 75, 76, 84, 85, 101, 119, 137, 151, 153, 183, 193, 195, 196, 199, 201, 205, 221 technological change, 148 technology(s), viii, 2, 15, 19, 20, 23, 60, 61, 120, 133, 136, 137, 149, 167, 170, 199 teeth, 128 temperature, 61, 64, 65, 69, 89, 90, 100, 103, 104, 110, 116, 132, 133, 135, 162, 177, 183, 184, 185, 198, 200, 212 tensile strength, 123, 126 tension(s), 20, 126, 127, 133, 141, 142, 143, 144, 153, 222, 225 terpenes, 123 terraces, 144 territorial, 2, 37, 40, 42, 194 territory, 3, 4, 6, 38, 41, 42, 43 testing, 164, 170 texture, 20, 121 thermal degradation, 65 thermodynamics, 228, 230 thinning, viii, 10, 11, 14, 15, 16, 19, 21, 22, 25, 26, 28, 29, 32, 35, 40, 42, 52, 113, 151, 152 threats, 88 three-dimensional reconstruction, 159 timber production, 5, 12, 17, 21, 25, 35, 106 time frame, 212 tissue, x, 95, 123, 207 tonality, 61 tones, 70, 71 total energy, 132 tourism, 5, 9, 32 trachea, 121 trade, 99, 101

trade-off, 99, 101 traits, 95, 195 transformation(s), 60, 61, 66, 68, 70, 71, 82, 120, 128, 178, 179, 183, 187, 196 transformation processes, 120 translation, 207, 216 transmission, 4 transpiration, 95, 215 transport, 60, 108, 220 transverse section, 122, 153 trauma, 158 treatment, 2, 16, 23, 28, 73, 75, 85, 107, 124, 135, 136, 229 trial, 131 trypsin, 199 turgor, 96, 97 turnover, 104 twist, 142

U UK, 117, 170, 215, 218 Ukraine, 62 UL, 204 uniform, 13, 73, 141 United Nations, 3, 47, 51 United States (USA), 34, 50, 51, 53, 54, 55, 57, 58, 62, 89, 190 urban, 42, 213 urea, 168 USDA, 50, 52, 149, 169, 170, 218 UV, 72, 148 UV irradiation, 72 UV radiation, 148

V vacuum, 132, 165 validation, 198 valuation, vii, 1, 2, 5, 6, 15, 20, 21, 23, 25, 42, 48, 49, 137, 141 vandalism, 44 variables, 26, 28, 89, 96, 156, 158, 161 variations, 15, 20, 97, 105, 115, 116, 126, 142, 146, 154, 167, 170 varieties, 70, 81, 206 vegetable oil, 178 vegetation, 4, 5, 6, 7, 9, 13, 33, 34, 35, 36, 38, 39, 40, 46, 53, 94, 97, 107, 111, 175 ventilation, 135 vessels, 62, 63, 120, 121, 122, 153, 154, 175, 176 videotape, 228

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Index volatilization, 74 vulnerability, 4, 96, 194

W

X xylem, 94, 95, 96, 97, 101, 113, 120, 121, 123, 203

Y yeast(s), 72, 73, 74, 77, 84, 187, 188 yield, 13, 16, 21, 23, 26, 27, 28, 29, 31, 41, 49, 50, 52, 63, 97, 98, 100, 108, 113, 141, 161, 170, 176, 195, 196

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war, 50 Washington, 216, 229 water absorption, 221 water evaporation, 36 water quality, 3, 32, 46 water resources, 48 WD, 218 weakness, 47, 133 wear, ix, 128, 146, 151, 162, 165, 166, 167 well-being, 3 wells, 43 Western Europe, 50, 51 wettability, 221, 228 wetting, 228 white oak, 62, 78, 121, 122, 145, 146, 176, 180, 190, 203, 216 wildlife, ix, 9, 37, 38, 39, 40, 41, 42, 43, 46, 51, 52, 53, 114, 193 wildlife conservation, 46 wind speed, 41 windows, 146, 153

wood composition, vii, 59, 63, 68 wood density, 124, 125, 153, 156, 157, 158, 167, 168, 169, 170, 171 wood products, 1, 2, 21, 32, 47, 76, 152, 153, 159, 167, 169 wood species, vii, x, 123, 130, 148, 165, 166, 219, 221, 222, 223, 224, 225, 226, 227, 228, 229 woodland, viii, 87, 94, 113, 213, 215, 216, 217, 218 woodland forest agroecosystem, viii, 87 wool, 109, 111 workers, 108, 224 workflow, 198 working conditions, 48

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