Vegetation ecology of Central Europe. Volume I, Ecology of Central European forests 978-3-319-43042-3, 3319430424, 978-3-319-43040-9

Table of contents :
Front Matter ....Pages i-xxxiv
Front Matter ....Pages 1-1
Environmental and Historical Influences on the Vegetation of Central Europe (Christoph Leuschner, Heinz Ellenberg)....Pages 3-21
Life Forms and Growth Types of Central European Plant Species (Christoph Leuschner, Heinz Ellenberg)....Pages 23-28
Front Matter ....Pages 29-29
The Central European Vegetation as the Result of Millennia of Human Activity (Christoph Leuschner, Heinz Ellenberg)....Pages 31-116
Front Matter ....Pages 117-117
Abiotic Conditions, Flora, Ecosystem Functions and Recent Human Influence (Christoph Leuschner, Heinz Ellenberg)....Pages 119-347
Front Matter ....Pages 349-349
Beech and Mixed Beech Forests (Christoph Leuschner, Heinz Ellenberg)....Pages 351-441
Mixed Broadleaved Forests Poor in Beech Outside of Floodplains or Mires (Christoph Leuschner, Heinz Ellenberg)....Pages 443-519
Pure and Mixed Coniferous Forests (Christoph Leuschner, Heinz Ellenberg)....Pages 521-606
Forest Plantations and Clearings (Christoph Leuschner, Heinz Ellenberg)....Pages 607-632
Woody Vegetation of Floodplains and Swamps (Christoph Leuschner, Heinz Ellenberg)....Pages 633-728
Epiphyte Vegetation (Christoph Leuschner, Heinz Ellenberg)....Pages 729-746
Forest Edges, Scrub, Hedges and Their Herb Communities (Christoph Leuschner, Heinz Ellenberg)....Pages 747-774
Syntaxonomic Overview of the Vascular Plant Communities of Central Europe: Forest and Scrub Formations (Christoph Leuschner, Heinz Ellenberg)....Pages 775-779
Back Matter ....Pages 781-971

Citation preview

Christoph Leuschner Heinz Ellenberg

Ecology of Central European Forests Vegetation Ecology of Central Europe Volume I

Ecology of Central European Forests

Christoph Leuschner  •  Heinz Ellenberg

Ecology of Central European Forests Vegetation Ecology of Central Europe, Volume I Revised and Extended Version of the 6th German Edition Translated by Laura Sutcliffe

Christoph Leuschner Plant Ecology University of Göttingen Göttingen, Germany

Heinz Ellenberg (deceased) University of Göttingen Göttingen, Germany

Translation of the revised and extended German language edition: Vegetation Mitteleuropas mit den Alpen, by Heinz Ellenberg/Christoph Leuschner, © 2010 by Eugen Ulmer KG, Stuttgart, Germany. All Rights Reserved. ISBN 978-3-319-43040-9    ISBN 978-3-319-43042-3 (eBook) DOI 10.1007/978-3-319-43042-3 Library of Congress Control Number: 2017943125 © Springer International Publishing Switzerland 2017 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Cover illustration: Beech primeval forest Havešová in Slovakia Printed on acid-free paper This Springer imprint is published by Springer Nature The registered company is Springer International Publishing AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Dedicated to the memory of Heinz Ellenberg (1913–1997), eminent ecologist, teacher and friend

Foreword

With the publication in 1963 of the first edition of his classical textbook Vegetation Mitteleuropas mit den Alpen (Vegetation Ecology of Central Europe), Heinz Ellenberg produced a unique compendium of the diverse vegetation types of Central Europe and their ecology. This region in the heart of Europe with more than 7000 years of continuous human settlement may well, together with Britain, be the best studied region on earth with respect to its vegetation ecology, visible in a myriad of publications on the floristics and plant communities, and the ecology of species, communities and ecosystems. Covering an area of approximately one million km2 in the northern temperate zone, Central Europe harbours a rich variety of landscapes from the Baltic and North Sea coasts in the north to the Alps in the south and from eastern France to eastern Poland. This diverse and well-studied region can provide profound insights into the complex interactions between environment, vegetation and man. Ellenberg’s concept was so successful because he based his analysis on a thorough description and sound classification of the plant communities, as many ecological statements lose value if they cannot be related to a particular community or vegetation type. It is on this foundation that causal relationships between environment, species composition, community dynamics and ecosystem functioning are explored for the main vegetation types. This truly interdisciplinary approach also includes the historical dimension of the vegetation, its recent change under the impact of human land use pressure and climate change, and current conservation issues. In the more than 50 years since the book’s first appearance, a tremendous amount of relevant research has been carried out, so that the task of providing a comprehensive overview of the plant, vegetation and ecosystem ecology of the Central European landscape mosaic has become even more challenging. However, the need for an interdisciplinary synthesis of facts and concepts in plant, vegetation and ecosystem ecology is also increasing. Most current environmental problems such as climate change, land use intensification, eutrophication or acid rain involve multifactorial causation, yet scientific training and research are increasingly narrowed into specialist fields. A broad synthesis of the existing ecological knowledge is vii

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Foreword

therefore vital to promote sound understanding of the ecosystem as a whole. This was the motivation for me to take on the task of producing an English version of the book using the 6th German edition as a basis (Ellenberg/Leuschner, 2010: Vegetation Mitteleuropas mit den Alpen, Ulmer Verlag). For the English book, most of the text was revised, a wealth of new facts added and more than 400 recent references incorporated (now over 5500 cited publications in total). For convenience, the book was split into two volumes (Vol. I, Ecology of Central European Forests; Vol. II, Ecology of Central European Non-Forest Vegetation), whereby Volume I also contains a general introduction into the physical geography, phytogeography and land use history of Central Europe. The book has greatly profited from the careful work and editing of Laura Sutcliffe who, as a native English speaker trained in ecology in Germany, had the task of translating the text. Many of the frameworks, classifications and other terminologies in the German-speaking ecological literature have developed independently of its Anglo-Saxon counterpart, and we spent many hours discussing how best to translate these. During the process of writing, many colleagues, fellow workers, students and technical assistants have supported me by supplying information, pointing at mistakes, correcting text passages, producing art work and helping to compile the references lists, especially Markus Hauck, Werner Härdtle, Dietrich Hertel, Michael Runge, Norbert Hölzel, Irmgard Blindow, Helge Walentowski, Yasmin Abou Rajab, Bernhard Schuldt, Jonas Glatthorn, Stefan Kaufmann and Ina C. Meier. I am very grateful to Bernd Raufeisen who produced all the figures and Astrid Röben who helped with the reference list. I would like to thank Valeria Rinaudo and Ineke Ravesloot from the Springer Editorial group and the production team around Prasad Gurunadham and S. Madhuriba for the dedication and support they gave this project. I hope that the two volumes of this book provide the reader with a useful and thought-provoking synthesis of the dynamics and functioning of Central European ecosystems with its characteristic vegetation types, habitats and landscapes. Clearly, such a book represents a subjective selection of topics and can cover only a fraction of the relevant publications, which is a severe shortcoming, but I hope that it serves to direct the reader to the relevant further reading. I am always grateful for corrections and any supplementary information. I hope above all that this book will continue to inspire current and future vegetation ecologists and provide a solid information platform for action to protect and value these landscapes. Göttingen, Germany March 2016

Christoph Leuschner

Contents of Volume I

Part I  The Natural Environment and Its History 1 Environmental and Historical Influences on the Vegetation of Central Europe.................................................................................... 3 1.1 The Climate and Phytogeography of Central Europe..................... 3 1.2 An Overview of the Geology and Soils of Central Europe............. 10 1.3 Historical Influences on the Vegetation of Central Europe............. 13 2 Life Forms and Growth Types of Central European Plant Species............................................................................................. 23 2.1 Life Forms....................................................................................... 23 2.2 Endogenous Rhythms..................................................................... 26 2.3 Plant Anatomy and  Morphology..................................................... 27 Part II  The Role of Man 3 The Central European Vegetation as the Result of Millennia of Human Activity.............................................................. 31 3.1 Phases of Forest Clearance............................................................. 31 3.2 The Effects on the Vegetation of Low-Intensity Grazing and Woodland Use............................................................. 40 3.2.1 The Opening Up and Destruction of the Forest................ 40 3.2.2 The Spread of Pasture Weeds............................................ 45 3.2.3 Soil Degradation Through Low-Intensity Grazing........... 47 3.3 From Coppiced Woodlands to Modern Forestry............................. 52 3.3.1 Coppicing With  and  Without Standards............................ 52 3.3.2 High Forest Management.................................................. 58 3.4 The Development of Arable Cultivation and Arable Weeds........... 60 3.4.1 Pre-industrial Agriculture.................................................. 60 3.4.2 The Effects of Technological Advances on Crop Fields and Low-Intensity Pastures............................................... 64

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3.5 The Development of Meadows, Intensive Pastures and Other Grassland........................................................................ 65 3.5.1 Straw and Fodder Meadows.............................................. 65 3.5.2 Continuous and Rotational Grazing.................................. 67 3.5.3 Agricultural Biocide Use, Energy Use and Crop Yield.... 69 3.6 Changes in Landscape Hydrology.................................................. 71 3.6.1 Modifications of River Valley Landscapes....................... 71 3.6.2 The North Sea Dykes and Their Consequences................ 74 3.6.3 The Destruction of Mires, and Attempts to Restore Them................................................................ 77 3.6.4 Increasing Exposure of the Vegetation to Drought........... 79 3.7 Chemical Pollution of the Environment and Its Impact on the Vegetation............................................................................. 79 3.7.1 Long- and Short-Range Effects of Chemical Pollutants... 79 3.7.2 Nutrient Enrichment of Soils and Water Bodies............... 80 3.7.3 Acid Deposition................................................................ 90 3.7.4 Sulphur Dioxide and Ozone Emissions............................ 92 3.7.5 Emissions of Heavy Metals and Other Substances........... 98 3.8 Changes in Game Densities and Their Effect on the Vegetation.... 104 3.9 Introduction of Non-native Plant Species....................................... 105 3.10 Recent Species Losses and Impoverishment of Plant Communities...................................................................... 106 3.11 The Effects of Recent Climate Change on the Vegetation.............. 108



Part III  General Ecology of Central European Forests 4 Abiotic Conditions, Flora, Ecosystem Functions and Recent Human Influence................................................................. 119 4.1 The Flora of Central European Forests........................................... 119 4.2 The Geographic Distribution of Forest Vegetation......................... 119 4.2.1 Zonal, Extrazonal and Azonal Forest Vegetation.............. 119 4.2.2 The Potential Natural Vegetation of Central Europe......... 123 4.2.3 Altitudinal Belts of Forest Vegetation............................... 124 4.2.4 Water and Temperature Limitations of Forest Growth...... 125 4.3 Environmental Conditions and Forest Habitat Classification......... 127 4.3.1 The Climate of the Forest Interior..................................... 127 4.3.2 Soil Water Regime............................................................ 134 4.3.3 Soil Chemical Properties................................................... 141 4.4 Comparative Ecology of Central European Tree Species............... 150 4.4.1 Important Characteristics of Crown Structure.................. 151 4.4.2 Traits Related to Productivity and Stress Tolerance......... 151 4.4.3 Nitrogen Acquisition......................................................... 165 4.4.4 Stress Tolerance................................................................. 166 4.4.5 Litter Quality and Tree Species Effects on the Soil.......... 179 4.4.6 Competitive Abilities of the Tree Species......................... 182

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4.4.7 The Effects of Elevation on Tree Growth......................... 188 4.4.8 The Influence of Climate on Elevational Changes in Tree Species Composition.............................. 191 4.4.9 Forest Cover in Central Europe and the Current Coverage of Major Tree Species....................................... 194 4.5 Forest Floor Plants and Shrubs of the Forest Interior: Ecological Niches and Ecological Grouping.................................. 196 4.5.1 Niches of Forest Shrubs.................................................... 196 4.5.2 Ecology of Forest Floor Plants.......................................... 207 4.5.3 The Ecological Grouping of Herbaceous Plants in Central European Broadleaved Forests.............. 243 4.6 Population Ecology of Forest Floor Plants..................................... 245 4.6.1 Phenology.......................................................................... 245 4.6.2 Life Cycles........................................................................ 249 4.7 Productivity and Cycling of Water and Nutrients........................... 252 4.7.1 The Biomass and Productivity of the Tree Layer............. 252 4.7.2 The Biomass and Productivity of the Herb Layer............. 266 4.7.3 Ecosystem Carbon Cycling............................................... 270 4.7.4 Water Cycling.................................................................... 272 4.7.5 Nutrient Cycling................................................................ 283 4.8 Vegetation Dynamics...................................................................... 298 4.8.1 Tree Layer Dynamics........................................................ 298 4.8.2 Fluctuations and Succession in the Herb Layer................ 298 4.9 Recent Human Influence................................................................. 300 4.9.1 Forest Damage in the Past and the Present....................... 300 4.9.2 Anthropogenic Changes in Forest Soil Conditions........... 301 4.9.3 Recent Tree Damage and Its Potential Causes.................. 310 4.9.4 Anthropogenic Changes in the Herb Layer and in the Cryptogam and Fungal Flora of Forests........... 324 4.9.5 Conservation and Restoration of Forests.......................... 337

Part IV  Forest and Shrub Formations 5 Beech and Mixed Beech Forests............................................................. 351 5.1 The Classification of Hardwood Broadleaved Forests.................... 351 5.2 The Classification of Beech Forests in Central and Western Europe........................................................................ 356 5.3 Beech Forests on Rendzina and Pararendzina................................ 361 5.3.1 Mesic Limestone Beech Forests (Hordelymo-Fagetum)...................................................... 361 5.3.2 Mull Beech Forests Rich in Wild Garlic........................... 366 5.3.3 Sedge Beech Forests on Dry Slopes (Carici-Fagetum)............................................................... 368 5.3.4 Beech Forests Without a Herb Layer (Fagetum nudum).............................................................. 372

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5.3.5 Yew-Beech and Seslerio-Fagetum Forests on Steep Slopes................................................................. 375 5.3.6 Montane Beech and Fir-Beech Forests............................. 379 5.3.7 Subalpine Sycamore-Beech Forests (Aceri-Fagetum)...... 388 5.4 Beech and Mixed Beech Forests on Moderately Fertile Cambisols............................................................................ 391 5.4.1 The Galio odorati-Fagetum and Related Communities..................................................................... 391 5.4.2 Mixed Beech Forests on Moist Soil.................................. 399 5.4.3 Beech and Mixed Beech Forests Rich in Ferns................ 403 5.4.4 Beech Forests Rich in Festuca altissima........................... 408 5.5 Beech and Oak-Beech Forests on Highly Acidic Soils................... 409 5.5.1 Moder Beech Forests (Luzulo-Fagenion)......................... 409 5.5.2 Climatic and Edaphic Forms of Moder Beech Forests and Oak-­Beech Forests......................................... 416 5.5.3 Acid Beech Forests on Limestone.................................... 421 5.6 A Comparison of the Habitats of Beech Forest Communities................................................................................... 422 5.7 Beech Forest Dynamics.................................................................. 424 5.7.1 The Inter- and Post-Glacial Development of Beech Forests................................................................ 424 5.7.2 Patch Dynamics of Beech Forests..................................... 429

6 Mixed Broadleaved Forests Poor in Beech Outside of Floodplains or Mires........................................................................... 443 6.1 Maple- and Ash-Rich Mixed Forests.............................................. 443 6.1.1 Habitat Classification of Maple and Ash Forests.............. 443 6.1.2 The Fraxino-Aceretum...................................................... 446 6.1.3 The Aceri-Fraxinetum....................................................... 450 6.1.4 The Carici remotae-Fraxinetum........................................ 452 6.2 Mixed Lime Forests........................................................................ 454 6.2.1 The Asperulo taurinae-Tilietum in the Alps...................... 454 6.2.2 Mixed Tilia cordata Forests Outside of the Alps............. 456 6.2.3 Thermophilic Mixed Large-Leaved Lime-Maple Forests (Aceri platanoidis-Tilietum platyphylli)........................................................................ 457 6.3 An Overview of the Mixed Oak Forests of Central Europe........... 459 6.4 Thermophilic Mixed Oak Forests (Quercetalia pubescentis)........ 461 6.4.1 ‘Relict’ Submediterranean Downy Oak Forests and Continental Steppe Forests......................................... 461 6.4.2 The Quercetalia pubescentis Across  a West-East Climatic and Floristic Gradient..................... 466 6.4.3 The Subcontinental Potentillo-Quercetum........................ 474 6.5 Mixed Oak Forests on Acid Soils................................................... 476 6.5.1 The Betulo-Quercetum and Related Communities in Central Europe........................................ 476

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6.5.2 Thermophilic Acid Oak Forests and Sweet Chestnut Coppices in Southern Central Europe............................... 490 6.6 Oak-Hornbeam Forests (Carpinion betuli)..................................... 494 6.6.1 Thermophilic Subcontinental Oak-Hornbeam Forests (Galio-­Carpinetum).............................................. 494 6.6.2 Moist Subatlantic Oak-Hornbeam Forests (Stellario-­Carpinetum)...................................................... 497 6.6.3 Beech-Rich Oak-Hornbeam Forests................................. 502 6.6.4 Lime-Hornbeam Forests (Tilio-Carpinetum) Outside the Range of Beech.............................................. 508 6.6.5 A Comparison of the Environmental Conditions in Oak-­­Hornbeam Forests............................... 518

7 Pure and Mixed Coniferous Forests....................................................... 521 7.1 The Role of Conifers in the Forests of Central Europe................... 521 7.2 The Systematic Classification of Conifer Forest Communities........................................................................ 525 7.3 Silver Fir Forests............................................................................. 526 7.3.1 The Unique Position of Fir Communities in Central European Forests.............................................. 526 7.3.2 Fir Forest Communities of the Alps and Their Foothills............................................................ 529 7.3.3 Fir Forests of Low Mountain Ranges and Lowlands.................................................................... 537 7.4 Spruce Forests................................................................................. 541 7.4.1 The Natural Range and Habitats of Spruce Forests in Central Europe.................................................. 541 7.4.2 The Systematic Classification of Spruce-Rich Conifer Forests.................................................................. 545 7.4.3 Montane and Subalpine Spruce Forests............................ 549 7.4.4 The Role of Spruce in Lowland Areas.............................. 556 7.4.5 Environmental Conditions in Various Spruce Forest Communities.......................................................... 558 7.5 Subalpine Larch-Swiss Stone Pine Forests and Larch Forests............................................................................ 560 7.5.1 Environmental Conditions of Larch and Swiss Stone Pine Forests in the Central Alps.............................. 560 7.5.2 Larch-Swiss Stone Pine Forests in the Alps and the Tatra...................................................................... 565 7.5.3 Larch Forests of the Southern Alps and  Non-Alpine Larch Stands.................................................. 570 7.6 Mountain Pine Stands Outside of Mires......................................... 571 7.6.1 Erect Mountain Pine Communities................................... 571 7.6.2 Dwarf Mountain Pine Scrub Under Different Environmental Conditions................................................ 574

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7.7 Pine Forests Outside of Mires and Floodplains.............................. 581 7.7.1 Central European Scots Pine Forests: Variation with Environmental Conditions......................... 581 7.7.2 Scots Pine and Black Pine Communities in the Alps......................................................................... 585 7.7.3 A Comparison of Pine and Mixed Oak Forests in the Pleistocene Lowlands.............................................. 590 7.8 Conifer Forest Dynamics................................................................ 598 7.8.1 Conifer Regeneration........................................................ 598 7.8.2 Stand Dynamics................................................................ 600

8 Forest Plantations and Clearings............................................................ 607 8.1 Plantation Communities in Comparison to Semi-natural Forest Communities........................................................................ 607 8.1.1 Types of  Plantation Vegetation.......................................... 607 8.1.2 Conifer Monocultures in Broadleaved Forest Habitats.................................................................. 622 8.1.3 The Vegetation of Clearings and Burnt Areas................... 626 9 Woody Vegetation of Floodplains and Swamps..................................... 633 9.1 Flora and  Origins............................................................................ 633 9.2 Habitat Conditions and Classification............................................. 636 9.2.1 Floodplain Morphology and Local Climate...................... 636 9.2.2 Soil Chemistry and Nutrient Supply................................. 640 9.2.3 Discharge Regime, Flooding Frequency and Soil Moisture.............................................................. 644 9.2.4 Stagnant and Flowing Groundwater................................. 648 9.3 Vegetation........................................................................................ 652 9.3.1 Woody Vegetation of Floodplains and Riverbanks........... 652 9.3.2 Swamp and Mire Forests................................................... 688 9.4 Adaptations to the Environment..................................................... 700 9.4.1 Flood Tolerance of Floodplain Species............................. 700 9.4.2 Summer Drought Stress in Floodplains............................ 705 9.4.3 Willows as Characteristic Species of Floodplains and Swamps...................................................................... 706 9.5 Population Biology and Community Ecology................................ 708 9.5.1 Phenology.......................................................................... 708 9.5.2 River Valleys as Migration Routes for  Mountain Species.............................................................. 709 9.5.3 Regeneration and Population Dynamics in Floodplain Forests......................................................... 712 9.6 Productivity and Cycling of Water and Nutrients........................... 715 9.6.1 Forest Structure, Biomass and Productivity...................... 715 9.6.2 Water and Nutrient Cycling.............................................. 716 9.7 Vegetation Dynamics...................................................................... 718 9.7.1 Dynamics of  Floodplain Vegetation.................................. 718

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9.7.2 Succession Following Disturbance................................... 721 9.8 Human Influence............................................................................. 722 9.8.1 Exploitation, Drainage and Destruction of Floodplain Forests........................................................ 722 9.8.2 Conservation and Restoration of Floodplain Forests........ 726

10 Epiphyte Vegetation................................................................................. 729 10.1 Tree Bark as an Epiphyte Substrate................................................ 729 10.2 Epiphytic Algal, Lichen and Bryophyte Communities................... 731 10.2.1 Alga-Rich Epiphyte Communities.................................... 732 10.2.2 Lichen-Rich Epiphyte Communities................................. 733 10.2.3 Bryophyte-Rich Epiphyte Communities........................... 734 10.3 Adaptations to the Environment..................................................... 737 10.3.1 Important Ecological Properties of Epiphytic Cryptogams....................................................................... 737 10.3.2 Carbon Assimilation as a Function of Moisture, Light Intensity and Temperature....................................... 738 10.3.3 Chemical and Physical Properties of the Substrate........... 740 10.3.4 The Effects of Toxic Substances and the Role of Epiphytes as Indicators................................................. 741 10.3.5 The Importance of Stand Structure and Stand Age........... 742 10.4 Recent Changes in Epiphyte Communities..................................... 743 1 1 Forest Edges, Scrub, Hedges and Their Herb Communities............... 747 11.1 Flora and  Development................................................................... 747 11.2 Environmental Conditions and Habitat Classification.................... 750 11.3 Vegetation........................................................................................ 756 11.3.1 Forest Edges, Scrub and Hedges....................................... 756 11.3.2 Herb Fringe Communities................................................. 763 11.4 Adaptations to the Environment, Population Biology and Vegetation Dynamics................................................................ 768 11.5 Human Influence............................................................................. 771 11.5.1 Decline and Destruction of Hedges.................................. 771 11.5.2 The Importance of Hedges for Agriculture and Agricultural Landscapes............................................. 773 12 Syntaxonomic Overview of the Vascular Plant Communities of Central Europe: Forest and Scrub Formations............................................................................. 775 References......................................................................................................... 781 Index.................................................................................................................. 891

Contents of Volume II

Part I  Natural or Near-Natural Formations 1 Salt Marshes and Inland Saline Habitats.............................................. 3 1.1 The Halophyte Flora of Central Europe.......................................... 3 1.2 Environmental Conditions and Habitat Classification.................... 5 1.2.1 The North Sea Intertidal Mudflats.................................... 5 1.2.2 The Baltic Coast................................................................ 8 1.3 Vegetation........................................................................................ 9 1.3.1 Classification of the North Sea Coastal Vegetation........... 9 1.3.2 The Baltic Sea Coastal Vegetation.................................... 21 1.3.3 Halophyte Vegetation in Inland Saline Habitats............... 31 1.4 Adaptations to the Environment..................................................... 34 1.4.1 Adaptations to  Salinity...................................................... 34 1.4.2 Adaptations to Flooding, Anoxia and Sedimentation....... 39 1.4.3 Adaptations to Low Nutrient Levels and Drought Stress............................................................ 42 1.5 Productivity and Nutrient Cycling.................................................. 43 1.6 Vegetation Dynamics...................................................................... 46 1.6.1 The Genesis of Salt Marshes............................................. 46 1.6.2 Zostera Community Dynamics......................................... 47 1.6.3 Succession in Salt Marsh Communities Caused by Sedimentation............................................................... 49 1.6.4 Succession on Bare Sand Banks....................................... 49 1.6.5 The Colonisation of a Muddy Island in the Baltic Sea................................................................ 52 1.7 Human Influence............................................................................. 53 1.7.1 Effects of Salt Marsh Grazing........................................... 53 1.7.2 Salt Marsh Succession After Abandonment of Grazing......................................................................... 56 1.7.3 Eutrophication of  Coastal Waters...................................... 57

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2 Sand Dunes and Their Vegetation Series............................................... 63 2.1 Flora and  Vegetation....................................................................... 63 2.2 Dune Formation and Destruction.................................................... 63 2.2.1 Coastal Dunes of the North Sea........................................ 64 2.2.2 Coastal Dunes of the Baltic Sea........................................ 71 2.3 Vegetation........................................................................................ 72 2.3.1 Coastal Dunes of the North Sea........................................ 72 2.3.2 Baltic Coastal Dunes......................................................... 85 2.3.3 Mobile Dunes Without Vegetation.................................... 90 2.3.4 Vegetation of Inland Dunes............................................... 92 2.4 Adaptations to the Environment..................................................... 98 2.4.1 Life at the Drift Line......................................................... 98 2.4.2 Adaptations to Coverage with Sand, Drought and Heat Stress.................................................................. 100 2.4.3 Adaptations to Low Nutrient Levels................................. 104 2.4.4 Dwarf Plants and Phreatophytes in Dune Slacks.............. 107 2.5 Vegetation Dynamics...................................................................... 108 2.5.1 Nutrient Accumulation and Soil Genesis During Dune Formation.................................................... 110 2.5.2 Changes to the Vegetation Caused by Invasive Species................................................................ 112 2.6 Human Influence............................................................................. 113 2.6.1 The Effects of Eutrophication and Drainage..................... 113 2.6.2 The Effects of Livestock Grazing, Rabbit Browsing and Afforestation............................................................... 114 3 Mires.......................................................................................................... 117 3.1 Flora................................................................................................ 118 3.2 Environmental Conditions and Habitat Classification.................... 120 3.2.1 Peat Formation and Decomposition.................................. 121 3.2.2 Surface Structure and Morphological Classification of Mires...................................................... 122 3.2.3 Macroclimate and Mire Formation................................... 129 3.2.4 Microclimate..................................................................... 131 3.2.5 Water Regimes and Hydrological Mire Types.................. 132 3.2.6 Nutrient Supply and Trophic Mire Types.......................... 137 3.3 Vegetation........................................................................................ 144 3.3.1 Synsystematic Overview................................................... 144 3.3.2 Communities of Raised Bog Hummocks and Wet Heaths (Oxycocco-Sphagnetea)......................... 145 3.3.3 Communities of Hollows in Oligotrophic Mires.............. 151 3.3.4 Acid to Basic Mesotrophic Mires..................................... 153 3.3.5 Calcareous Mesotrophic Fens........................................... 156

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3.4 Adaptations to the Environment..................................................... 159 3.4.1 Adaptations to Drought, Flooding and Anoxic Conditions...................................................... 159 3.4.2 Adaptations to Low Nutrient Levels and the Role of Base Richness.......................................... 162 3.5 Productivity and Cycling of Water and Nutrients........................... 165 3.5.1 Productivity....................................................................... 165 3.5.2 Peat Accumulation and  Decomposition............................ 168 3.5.3 Water and Nutrient Cycling.............................................. 169 3.6 Vegetation Dynamics...................................................................... 172 3.6.1 Quaternary Mire Development......................................... 172 3.6.2 Recent Developmental Processes...................................... 176 3.6.3 Primary Succession in Growing Raised Bogs................... 178 3.6.4 Secondary Succession After Mire Drainage..................... 179 3.7 Human Influence............................................................................. 179 3.7.1 Exploitation by Peat Cutting, Drainage and Cultivation.................................................................. 179 3.7.2 Eutrophication................................................................... 183 3.7.3 Accumulation of Pollutants and Exchange of Trace Gases with the Atmosphere................................. 184 3.7.4 Conservation and Restoration of Mires............................ 185

4 Vegetation of Freshwater Habitats......................................................... 189 4.1 Freshwater Macrophytes and Their Origins.................................... 189 4.2 Environmental Conditions and Habitat Classification.................... 190 4.2.1 Physical Characteristics.................................................... 191 4.2.2 Chemical Characteristics................................................... 194 4.2.3 Ecological Classification of Freshwater Systems............. 198 4.3 Vegetation........................................................................................ 204 4.3.1 The Classification of Aquatic Plant Communities............ 204 4.3.2 Still Water Bodies.............................................................. 206 4.3.3 Streams and  Rivers............................................................ 224 4.3.4 Communities of  Springs.................................................... 232 4.4 Adaptations to the Environment..................................................... 235 4.4.1 Photosynthesis in  Aquatic Plants...................................... 235 4.4.2 Nutrient Uptake by Aquatic Plants.................................... 237 4.4.3 Survival in Hypoxic Sediments......................................... 238 4.4.4 Adaptations to Flowing Water and Wave Action.............. 239 4.4.5 Life Forms and Morphological Adaptations of Aquatic Plants............................................................... 241 4.5 Population Biology and Community Ecology................................ 243 4.5.1 Phenology.......................................................................... 243 4.5.2 Life Cycles of Aquatic Plants............................................ 243 4.5.3 Interspecific Competition Between Aquatic Plant Species..................................................................... 247

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4.6 Productivity and Cycling of Water and Nutrients........................... 249 4.6.1 Productivity....................................................................... 249 4.6.2 Water Cycling.................................................................... 252 4.6.3 Nutrient Cycling................................................................ 253 4.7 Vegetation Dynamics...................................................................... 254 4.7.1 Seasonal and Interannual Fluctuations.............................. 254 4.7.2 Long-Term Dynamics and Succession in Lakes............... 256 4.7.3 Self-Purification of Water Bodies as Secondary Succession......................................................................... 257 4.8 Human Influence............................................................................. 259 4.8.1 Eutrophication of  Water Bodies........................................ 259 4.8.2 Acidification...................................................................... 264 4.8.3 Reedbed Dieback.............................................................. 266 4.8.4 Threats to and Conservation of Freshwater Habitats........ 267

5 Vegetation of the Alpine and Nival Belts................................................ 271 5.1 Flora and  Development................................................................... 271 5.2 Environmental Conditions and Habitat Classification.................... 276 5.2.1 The High Mountain Climate............................................. 276 5.2.2 Soils and Nutrient Supply................................................. 291 5.2.3 Soil Moisture Regime....................................................... 294 5.3 Vegetation........................................................................................ 296 5.3.1 Vegetation Zonation in the High Mountains..................... 296 5.3.2 Vegetation Mosaics in the Subalpine Belt and at the Tree Line........................................................... 298 5.3.3 Ecological and Synsystematic Classifications of Alpine Vegetation.......................................................... 299 5.3.4 Vegetation Mosaics in the Nival Belt................................ 301 5.3.5 Subalpine-Alpine Grasslands on Carbonate Bedrock (Class Seslerietea albicantis)........................... 304 5.3.6 Carici rupestris-Kobresietea bellardii (Wind-Edge Naked Rush Swards).................................... 314 5.3.7 Subalpine-Alpine Grasslands on Acid Soil (Class Caricetea curvulae).............................................. 316 5.3.8 Subalpine-Alpine Dwarf Shrub Heaths (Class Loiseleurio-­Vaccinietea)....................................... 323 5.3.9 Class Salicetea herbaceae and Alliance Arabidion caeruleae........................................................ 328 5.3.10 Subalpine-Alpine Mires, Springs and Flooded Banks................................................................................. 335 5.3.11 Subalpine-Alpine Tall-Herb Communities and  Green Alder Scrub (Class Betulo-Adenostyletea and Betulo-­Alnetea viridis)............................................ 344

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5.3.12 The Class Thlaspietea rotundifolii of Carbonate Scree Slopes................................................ 351 5.3.13 The Vegetation of  Rocky Areas (Class Asplenietea trichomanis and Others).................... 358 5.3.14 Plant Communities of the Nival Belt................................ 368 5.4 Adaptations to the Environment..................................................... 374 5.4.1 Adaptations to High and Low Temperatures..................... 374 5.4.2 Carbon Gain and  Turnover................................................ 379 5.4.3 Nutrient Acquisition by  Alpine Plants and Adaptations to Basic and Acidic Soils........................ 385 5.4.4 Characteristic Life Forms in the Alpine and Nival Belts.................................................................. 391 5.4.5 The Structure and Causes of the Alpine Tree Line........... 394 5.5 Population Biology and Community Ecology................................ 403 5.5.1 The Growth and Developmental Rhythms of Alpine Plants................................................................. 403 5.5.2 Diaspore Dispersal and Seedling Establishment............... 405 5.6 Productivity and Cycling of Water and Nutrients........................... 406 5.6.1 Productivity....................................................................... 406 5.6.2 Water and Nutrient Cycling.............................................. 408 5.7 Vegetation Dynamics...................................................................... 411 5.7.1 Primary Succession on Glacier Forelands........................ 411 5.7.2 Changes in the Vegetation as a Result of Climate Change............................................................ 423 5.8 Human Influence............................................................................. 427 5.8.1 Changes in Land Use and Eutrophication at High Elevations............................................................. 427 5.8.2 The Threat to Alpine Vegetation Posed by Tourism and Restoration Approaches.............................................. 428

Part II  Partly or Mostly Anthropogenic Formations 6 Dwarf Shrub Heaths and Nardus Grasslands....................................... 435 6.1 Flora and  Development................................................................... 435 6.2 Environmental Conditions and Habitat Classification.................... 440 6.2.1 Climatic Conditions and Water Regime............................ 441 6.2.2 Stand Structure and Microclimate..................................... 442 6.2.3 Soils and Nutrient Supply................................................. 442 6.3 Vegetation........................................................................................ 446 6.3.1 Nardus Grasslands (Order Nardetalia strictae).............. 446 6.3.2 Dwarf Shrub Heaths (Order Vaccinio-Genistetalia)........ 452 6.4 Adaptations to the Environment..................................................... 470 6.4.1 Growth Form and Light Demand...................................... 470 6.4.2 Adaptations to Low Nutrient Availability and Unfavourable Soil Chemical Conditions.................... 471 6.4.3 Adaptations to Drought and Frost..................................... 474

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6.5 Population Biology and Community Ecology................................ 474 6.6 Productivity and Water and Nutrient Cycling................................. 475 6.6.1 Productivity....................................................................... 475 6.6.2 Water and Nutrient Cycling.............................................. 478 6.7 Vegetation Dynamics...................................................................... 480 6.7.1 Fluctuations and ‘Cyclical Succession’............................. 480 6.7.2 Succession Following Disturbance................................... 481 6.7.3 Succession to  Forest.......................................................... 482 6.8 Human Influence............................................................................. 487 6.8.1 Grazing and  Mowing........................................................ 487 6.8.2 Eutrophication and  Acidification...................................... 488 6.8.3 Conservation and Restoration of Heathland and Nardus Grasslands...................................................... 491

7 Nutrient-Poor Dry Grasslands................................................................ 495 7.1 Flora and  Development................................................................... 495 7.1.1 Flora.................................................................................. 495 7.1.2 The Role of the Climate and Humans in the Development of Dry Grasslands............................. 497 7.2 Environmental Conditions and Habitat Classification.................... 499 7.2.1 Aspect and  Microclimate.................................................. 500 7.2.2 Soil Moisture Regime....................................................... 505 7.2.3 Soil Types and Their Nutrient Supply............................... 512 7.3 Vegetation........................................................................................ 514 7.3.1 Classification of the Major Habitat Types......................... 514 7.3.2 Calcareous Dry Grasslands (Class Festuco-Brometea)................................................ 522 7.3.3 Sandy Dry Grasslands and Vegetation of Cliffs and Rocky Debris (Class Koelerio-Corynephoretea).............................................. 538 7.4 Adaptations to the Environment..................................................... 545 7.4.1 Adaptations to  Drought..................................................... 545 7.4.2 Adaptations to Nutrient Shortage...................................... 561 7.4.3 Adaptation to Heat Stress.................................................. 565 7.4.4 Adaptations to Basic and Acidic Soils.............................. 565 7.5 Population Biology and Community Ecology................................ 566 7.5.1 Phenology.......................................................................... 566 7.5.2 Seed Bank, Germination and Dispersal............................ 567 7.5.3 The Influence of Competition on the Species Composition...................................................................... 570 7.5.4 The Causes of Species Richness in Dry Grasslands......... 573 7.6 Productivity and Cycling of Water and Nutrients........................... 576 7.6.1 Productivity....................................................................... 576 7.6.2 Water and Nutrient Cycling.............................................. 578

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7.7 Vegetation Dynamics...................................................................... 581 7.7.1 Primary Succession on Rock Debris and Opencast Mine Areas................................................. 581 7.7.2 Short- and Mid-term Changes in Dry Grasslands............. 582 7.7.3 Secondary Succession in Abandoned Dry Grasslands...... 584 7.7.4 The Development of Steppe-Like Grasslands on Abandoned Fields......................................................... 586 7.8 Human Influence............................................................................. 587 7.8.1 Mown and Grazed Dry Grasslands................................... 587 7.8.2 Eutrophication................................................................... 591 7.8.3 Habitat Fragmentation....................................................... 592 7.8.4 Conservation and Restoration of Dry Grasslands............. 593

8 Agricultural Grassland on Mesic to Wet Soils...................................... 597 8.1 Flora and  Development................................................................... 598 8.1.1 Flora.................................................................................. 598 8.1.2 The Creation of Meadows and Pastures............................ 600 8.2 Environmental Conditions and Habitat Classification.................... 602 8.2.1 Grazing and Mowing as Key Site Factors........................ 602 8.2.2 Stand Structure and Microclimate..................................... 608 8.2.3 Soil Moisture Regime....................................................... 610 8.2.4 Soil Chemical Properties................................................... 619 8.3 The Vegetation of  Agricultural Grasslands and Roadside Verges....................................................................... 622 8.3.1 Overview of the Agricultural Grassland Communities of Central Europe....................................... 622 8.3.2 Mesic Meadows................................................................ 625 8.3.3 Wet Meadows.................................................................... 644 8.3.4 Filipendula Riverbank and Similar Tall Forb Communities..................................................................... 656 8.3.5 Grass Verges and  Traditional Orchards............................. 657 8.3.6 Pastures and Frequently Mown Grasslands...................... 661 8.3.7 Vegetation of Trampled Ground and Flooded Grassland........................................................................... 666 8.4 Adaptations to the Environment..................................................... 671 8.4.1 Tolerance of Mowing and Trampling................................ 671 8.4.2 Some Ecophysiological Properties of Grassland Species......................................................... 678 8.5 Population Biology and Community Ecology................................ 688 8.5.1 Phenology.......................................................................... 688 8.5.2 Seed Bank, Germination and Dispersal............................ 690 8.6 Productivity and Cycling of Water and Nutrients........................... 693 8.6.1 Productivity....................................................................... 693 8.6.2 Water and Nutrient Cycling.............................................. 701

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8.7 Vegetation Dynamics...................................................................... 706 8.7.1 The Establishment of Meadow Communities and the Importance of Stand History................................ 706 8.7.2 Succession in  Abandoned Meadows................................. 707 8.8 Human Influence............................................................................. 709 8.8.1 The Effects of Management Intensification and Fertilisation................................................................. 709 8.8.2 The Effects of Drainage and Irrigation............................. 720 8.8.3 Conservation and Restoration of Meadows...................... 727

9 Communities on Heavy Metal-Rich Soils.............................................. 733 9.1 The Origins and Development of the Heavy Metal Flora............... 734 9.2 Heavy Metal Soils........................................................................... 735 9.3 Vegetation........................................................................................ 738 9.3.1 Vascular Plant Communities............................................. 738 9.3.2 Lichen Vegetation.............................................................. 739 9.4 Adaptations to the Environment..................................................... 740 9.4.1 Heavy Metal Soils with Low Magnesium Concentrations.................................................................. 740 9.4.2 Heavy Metal Soils with High Magnesium Concentrations.................................................................. 745 9.5 Vegetation Dynamics...................................................................... 746 9.6 The Effects of Heavy Metal Deposition on the Vegetation............. 746 10 Banks, Shorelines and Muddy Habitats Influenced by Man............... 751 10.1 Short-Lived Isoëto-Nanojuncetea Communities on Periodically Wet Soils................................................................ 751 10.1.1 Range and Dispersal of the Nanocyperetalia................... 751 10.1.2 Vegetation.......................................................................... 753 10.1.3 Environmental Adaptations and  Vegetation Dynamics.......................................................................... 756 10.2 Nitrophilic Bidentetea Communities of Still and Flowing Water Bodies.............................................................. 757 10.2.1 Environmental Conditions and Habitat Classification..................................................................... 757 10.2.2 Vegetation.......................................................................... 760 10.2.3 Environmental Adaptations and  Vegetation Dynamics.......................................................................... 762 11 Ruderal Communities on Drier Soils..................................................... 765 11.1 Flora and  Development................................................................... 765 11.2 Environmental Conditions and Habitat Classification.................... 768 11.3 Vegetation........................................................................................ 769 11.3.1 Ruderal Communities of Summer and Winter Annuals........................................................... 769 11.3.2 Communities of Perennial Ruderal Plants........................ 773 11.4 Adaptations to the Environment..................................................... 777

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1 2 Vegetation of Arable Fields, Gardens and Vineyards........................... 779 12.1 Flora and  Development................................................................... 779 12.1.1 Flora.................................................................................. 779 12.1.2 The Origins of Arable Weeds and Changes in the Segetal Vegetation Since the Neolithic................... 780 12.2 Environmental Conditions and Habitat Classification.................... 783 12.2.1 Microclimate..................................................................... 783 12.2.2 Soil Moisture Regime....................................................... 784 12.2.3 Soil Acidity and Nutrient Supply...................................... 784 12.3 Vegetation........................................................................................ 786 12.3.1 Classification of  Arable Communities.............................. 786 12.3.2 Synsystematic Overview................................................... 788 12.4 Adaptations to the Environment..................................................... 794 12.4.1 Arable Plant Functional Types.......................................... 794 12.4.2 Germination Conditions and Light and Temperature Requirements.................................................................... 798 12.4.3 Adaptations to Moisture and Aeration of the Soil............. 800 12.4.4 Adaptations to the Nutrient Regime and the Effects of Fertiliser Application.................................................... 803 12.4.5 The Effects of Cultivation................................................. 809 12.4.6 The Effects of Herbicide Application............................... 811 12.5 Population Biology and Community Ecology................................ 813 12.5.1 Phenology.......................................................................... 813 12.5.2 Diaspore Banks and Dispersal.......................................... 813 12.5.3 Population Dynamics........................................................ 818 12.6 Productivity and Cycling of Water and Nutrients........................... 819 12.6.1 Water Cycling.................................................................... 819 12.6.2 Nutrient Cycling................................................................ 820 12.7 Vegetation Dynamics...................................................................... 822 12.7.1 Interannual Fluctuations and Changes with Crop Rotation............................................................ 822 12.7.2 Secondary Succession on Arable Fallows......................... 823 12.8 Human Influence............................................................................. 829 12.8.1 The Recent Collapse of Arable Weed Populations and Its Causes................................................ 829 12.8.2 Conservation and Restoration of Arable Weed Vegetation................................................................ 836 1 3 Vegetation of Human Settlements.......................................................... 841 13.1 The Flora of Towns and Villages and Its Origins............................ 841 13.2 Environmental Conditions and Habitat Classification.................... 846 13.3 Vegetation........................................................................................ 847 13.4 Adaptations to the Environment..................................................... 855 13.5 Vegetation Dynamics...................................................................... 858

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14 Syntaxonomic Overview of the Vascular Plant Communities of Central Europe: Non-Forest Formations.......................................... 861 References......................................................................................................... 873 Index.................................................................................................................. 1013

Directions for Use

This volume deals with the forests and scrub vegetation of Central Europe, be it natural or man-made, whilst Volume II is dedicated to the open habitats containing non-­forest vegetation such as mires, grasslands, heaths and alpine habitats. Volume I consists of 11 chapters and ends with a summarising chapter (12) on the synsystematic classification of these formations. Chapters 1 and 2 present the climatic, geological and pedological characteristics of Central Europe and provide a short introduction to its phytogeography. Chapter 3 gives a concise overview of the pervasive impact of man on the ecosystems and landscapes of this region over the last 7000 years, referring to both forests and non-forest vegetation. General aspects of the ecology of Central European tree species and forests are summarised in Chap. 4, which also contains a brief review of recent anthropogenic stressors of forest ecosystems, notably overuse, climate change, and the atmospheric deposition of nitrogen and strong acids. Chapters 5, 6 and 7 deal with the broadleaved and coniferous forest communities not shaped by flooding or high water tables. Forest plantations are the topic of Chap. 8, followed by floodplain and swamp forests (Chap. 9), forest epiphytic vegetation (Chap. 10), and the scrub vegetation of forest edges and hedges (Chap. 11). This book is based on the Central European system of floristically defined (phytosociological) vegetation types, which allows us to analyse the spectrum of natural and man-made ecosystems and gives insights into their ecology and dynamics. The vegetation classification system most widely used in Central Europe is the one introduced by Josias Braun-Blanquet around 100 years ago, which was subsequently modified and combined with numerical vegetation analysis. It uses diagnostic species (‘character species’ and ‘differential species’) to identify combinations of plant species that co-occur on a regular basis and thus can be considered as community types (syntaxa). Analogous to the taxonomic system of classification, syntaxa are organised in hierarchical levels of relatedness. This book does not attempt to give a complete syntaxonomic overview of the Central European vegetation but instead refers to existing syntheses, notably the work of Oberdorfer et al. (1987– 1992) and Oberdorfer (ed., 1992–1998), Pott (1995), Dierschke (1996 et seqq.) and Rennwald (2000) for Germany, of Chytrý (2007 et seqq.) for Czech Republic, of xxvii

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Schaminée et al. (1995 et seqq.) for the Netherlands, and of Mucina et al. (1993) and Willner and Grabherr (2007) for Austria. Here, only the widespread community types that are frequently referred to in the literature (associations, together with alliances and orders) will be presented. To highlight the most important associations, their names are underlined when mentioned for the first time in the text. An overview of the most important higher syntaxonomic units (classes, orders, alliances) is given in Chap. 12 (in Vol. I, forest and scrub vegetation) and 14 (in Vol. II, non-­ forest vegetation). The coverage of species in a relevé is indicated in the vegetation tables by the numbers 1–5 and the symbol + (+ = rare, 1 = 30 °C) has increased in Germany since the 1950s from around 3 to ~6 in 2000–2010 (Becker et al. 2012). In Valais in Switzerland, the number of days

Fig. 3.60  Annual variation in summer temperature (June–August) between 1864 and 2015 in Switzerland, compared to the average temperature 1961–1990 (Based on MeteoSchweiz 2016, www.meteosuisse.ch)

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Fig. 3.61  Temperature increase since 1953 of the surface waters of river Rhine (at Basel) and river Aare (at Berne, Switzerland) (Modified from Bundesamt für Umwelt (Switzerland) in International Commission for the Protection of the Rhine, Koblenz. www.iksr.org/fileadmin/user_upload/ Dokumente_en/Reports/209_e.pdf (accessed 15/02/2016))

Fig. 3.62  Temperature increase of the surface waters in the northern Wadden Sea near List/Sylt since 1951 (Modified from ‘Strategie für das Wattenmeer’ (https://www.schleswig-holstein.de/ DE/Fachinhalte/nationalpark_wattenmeer/bericht_strategie_wattenmeer2100.pdf?_ blob=publicationFile&v=4 (accessed 15/02/2016))

with average temperatures of above 20 °C have risen from 22 in 1980 to around 40 today (Rigling et al. 2006). A particularly large temperature increase has been observed in urban areas; for example, an increase by 2.1 K was recorded in Frankfurt am Main in the 60-year period 1950–2010. Significant temperature increases were also measured in freshwater and marine ecosystems. For example, the annual mean

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Fig. 3.63  Linear trends in summer precipitation in Germany between 1901 and 2000 in mm (white = increase, grey or hatched = decrease) (Adapted from Schönwiese and Janoschitz 2008)

water temperature of the Rhine in Weil (near Basel) increased from around 10 °C in 1950 to around 13 °C in 2010 (Fig. 3.61); a temperature increase by about 2 K was recorded between 1962 and 2008 in the coastal waters of the Wadden Sea near Sylt (Fig. 3.62). The temperature increase is associated with a decrease in the length of the winter frost period, whereby warm temperatures are being recorded earlier in the year. In the Fichtel Mountains (southern Germany), for example, the number of days with snow cover decreased between 1961/1962 and 2001/2002 by around 25 % (Foken 2004), and similar patterns have been found in Switzerland, the Swabian Jura (Elsässer and Bürki 2002; Kirchgäßner 2001) and elsewhere in Central Europe (European Environment Agency 2012). Despite the increases in temperature, a shorter period of snow cover in winter could increase the risk of frost damage for hemicryptophytes and geophytes. Observed Changes in Precipitation  Climate warming also leads to changes in precipitation and evaporation patterns. The global average annual precipitation has increased by 11–30 mm between 1901 and 2012 (IPCC 2013). Some regions of Central Europe have experienced reductions in precipitation over this period, and further decreases are predicted, whilst other areas have seen increases (Schönwiese

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et al. 2003; Fig. 3.63). In particular, increases in winter precipitation are expected, with more frequent extreme rainfall events, which may lead to increased flooding (Frei et al. 2006). Summer precipitation will, in contrast, probably decrease in frequency and amount in many regions of Central Europe (Rowell and Jones 2006), particularly in eastern Germany, in Poland and in parts of Switzerland with a more continental climate. In recent years, reductions in summer precipitation (June-­ August) have already been seen, for example, in parts of Saxony-Anhalt and Saxony by 50–60 mm (between 1901 and 2000) and in the Swabian Jura by around 57 mm (1960–1990; Rapp and Schönwiese 1996, Kirchgäßner 2001, Fabig 2007; Fig. 3.63). In Ticino in southern Switzerland, the number of extreme drought periods has increased considerably since 1980 (Rebetez 1999). There are reports of long-term decreases in soil moisture and the water table due to recent climate warming and drying from several Central European regions. For example, in certain regions in Brandenburg (eastern Germany) the soil moisture reserves have reduced by up to 15 mm since the 1950s (Holsten et al. 2013) and the water table decreased by 3 cm per year (Gerstengarbe et al. 2003). Higher summer temperatures increase the ­atmospheric evaporative demand, thereby further enhancing effects of reduced summer precipitation. Causes of Climate Change  The main cause of the recent warming has been the emissions of greenhouse gases caused by human activity, including CO2, N2O and CH4 (IPCC 2013). Between 1750 and 2015, the CO2 concentration in the atmosphere rose from around 280 to 400 ppm. Around 40 % of CO2 emissions over the last two centuries are thought to have come from changes in vegetation cover on earth, above all deforestation, whilst 60 % were released by the burning of fossil fuels (DeFries et al. 1999). Forty percent of the CO2 has remained in the atmosphere, 30 % dissolved into the oceans, and 25 % was reabsorbed into the biomass of terrestrial ecosystems (House et al. 2002). A consequence of rising temperatures and the melting of the ice caps will be a sea level rise by 30–100 cm by the end of the twenty-first century. Consequences for Plant Phenology  There are already numerous reports of the effects of climate change in recent decades on the ecosystems of Central Europe and their plant communities (summaries e.g. in Walther et al. 2002; Mosbrugger et al. 2012; Essl and Rabitsch 2013; European Environment Agency 2012). Based on the prognoses of the IPCC (2013), further fundamental changes in the structure and function of Central European ecosystems must be expected. Changes are particularly likely (1) in the phenology and productivity of plant species, (2) in the frequency and distribution of species, (3) in the composition of plant communities and in the interactions between species, and (4) in the nutrient cycles and other important ecosystem functions. The warming in recent decades has led to earlier foliation of trees, shrubs and spring geophytes, i.e. to an earlier start of the growing season. For example, in Germany over the period between 1951 and 1996, the leaves of beech, English oak, birch and horse chestnut appeared on average between 0.06 and 0.13 days earlier

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3  The Central European Vegetation as the Result of Millennia of Human Activity

Fig. 3.64  Foliation of beech and birch at 160 German measuring stations between 1950 and 2000 (boxes: 25–75 %, whiskers: 5 and 95 % of values) (From Menzel 2003)

per year. The leaves therefore now appear 3–7 days earlier than they did 50 years ago, corresponding to a shift of 2.5–6.7 days per degree increase in temperature (Menzel 2003). Similar trends were also observed in other tree species and in other regions of Central Europe (e.g. Defila and Clot 2005; Estrella et al. 2009). An average spring advancement of 4–5 days per 1 K increase has been observed in Europe (Amano et al. 2010; Estrella et al. 2009). The earlier foliation in trees has been particularly noticeable since 1985 (see Fig. 3.64). Snowdrops flower in Germany today around 2 weeks earlier than at the beginning of the 1960s (see Fig. 3.65), and the spring flowering phase of many species in species-rich deciduous forests has shifted forward by up to a month since 1989 (Dierschke 2000).

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Fig. 3.65  Start of snowdrop flowering between 1961 and 2005 (German average) (From Umweltbundesamt (ed., 2005)) Table 3.5  Trends in the foliation date and the length of the growing season of five tree species, and time of snowdrop flowering in Germany between 1951 and 1996

Phenological phase Betula pendula, leaf unfolding Fagus sylvatica, leaf unfolding Quercus robur, leaf unfolding Picea abies, new shoots Aesculus hippocastanum, leaf enfolding Betula pendula, length of growth period Fagus sylvatica, length of growth period Quercus robur, length of growth period Aesculus hippocastanum, length of growth period Galanthus nivalis, flowering

Trend (days per year) −0.13 −0.06 −0.12 −0.13 −0.16 +0.18 +0.10 +0.18 +0.14 −0.18

After Menzel (2003). During this period, snowdrop flowering advanced by around 8 days, birch leaves appeared 6 days earlier and beech profited from a growing season that was 4.5 days longer

The length of the growing season has increased by 5 days for beech, and 7–9 days for birch, oak and horse chestnut in the last 50 years, corresponding to an increase of 3–5 % (see Table 3.5). These changes are tightly linked to the NAO (North Atlantic Oscillation) Index for January and February. Positive NAO indices mean warm and damp conditions in Central Europe and therefore a longer growing season (see Fig. 3.66).

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Fig. 3.66  Anomalies in the length of the growing seasons of four tree species (European beech, silver birch, common oak, horse chestnut) and changes in the North Atlantic Oscillation (NAO) index for January/February in Germany between 1950 and 2000 (r2 = 0.41–0.44) (From Menzel 2003; with permission of Springer Science+Business Media)

Fig. 3.67  Volumes of wood blown down by storms in Germany and Switzerland since 1900 (From Steinmeyer (1991) and Wandeler and Günther (1991) in Puhe and Ulrich (2001))

The increase in extreme storm events in Central Europe is also probably a result of the higher temperatures. Above all in Germany, but also in other Central European countries, the volume of storm thrown wood has increased considerably since the 1970s (see Fig. 3.67). Changes in Plant Distribution  Global warming promotes the establishment of more thermophilic plant species in Central Europe. These are mostly neophytes

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Fig. 3.68  Reduction in the number of frost days per year (dots) and 5-year-­ average (line), and increase in the number of spreading evergreen exotic species in southern Switzerland since 1990 (From Walther et al. 2002; with permission of Nature Publishing Group)

introduced by humans, and establish most successfully in regions with warm summers, such as the Upper Rhine Plain, Burgenland or in the heat islands of cities (see Sect. 13.2 in Volume II). The thermophilic neophytes include numerous species of Poaceae with C4 photosynthetic pathway, which are today a permanent element of ruderal communities in warm locations, but also subtropical floating aquatic plants like Wolffia arrhiza and Salvinia natans. The latter have spread particularly in the warm Upper Rhine Plain, but also e.g. in the region of Bremen (Kesel and Gödeke 1996). In Ticino, the establishment of evergreen laurophyll shrubs and even the Chinese windmill palm (Trachycarpus fortunei) has been recorded in the temperate deciduous forests of the region (Gianoni et al. 1988; Walther 2000). Most of the laurophyll shrubs are escapees from gardens, which obviously benefit from the mild winters and the decreasing number of frost days in southern Switzerland (see Fig. 3.68). The increase in altitude of alpine plants (see Sect. 5.7.2 in Volume II), and in some regions of the Alps the recent elevation in the timber line (e.g. Nola 1994), have both been well documented, and attributed mainly to global warming (see Sects. 5.4.5.2 and 5.7.2 in Volume II, and 4.4.5 in this volume). Nevertheless, the increase in altitude of the alpine timber line has in many places not been as much as was expected, or it has not occurred at all (e.g. Hättenschwiler and Körner 1995; Paulsen et al. 2000). One reason for this is probably that mountain pine and spruce establish only slowly around the timber line (Dullinger et al. 2004). In the montane

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areas of Scandinavia, however, the increase in the tree line has been clearly visible, above all in the warmer years of 1996–2006 (Kullman 2002, 2007). A northward and eastward expansion of the distribution ranges of several species has been observed in the past decades. A well-documented example is holly (Ilex aquifolium) which has spread in eastern Germany, southern Sweden and in Norway during the last 50 years (Walther et al. 2005). System Responses  It is certain that climate change will also influence many ecosystem functions. Warming accelerates the decomposition of organic substances and reduces soil carbon content, thereby further increasing the release of CO2 if more carbon dioxide is not sequestered through increased photosynthesis. The increased decomposition rates primarily affect the compounds that are most easily broken down (e.g. Rustad and Fernandez 1998). Methane and nitrous oxide can also be released under increasing temperatures. These emissions are mainly dependent on soil moisture and land use, making trends in the coming decades difficult to predict accurately (Hassan et al. 2005).

Part III

General Ecology of Central European Forests

Chapter 4

Abiotic Conditions, Flora, Ecosystem Functions and Recent Human Influence

4.1  The Flora of Central European Forests Central Europe is home to only around 75 native tree species, 66 of which are native to Germany (Schmidt et al. 2003): the most important genera of these were listed in Table 1.1. The true forest species include a further 208 herbaceous plants that depend on closed-canopy forest and its characteristic abiotic conditions, as well as 17 shrub species. In contrast, the number of species that thrive in forest edges, clearings or disturbed forest, i.e. occurring both in forests and in open areas, is much higher both for herbs (814) and for shrubs (94). An additional 900 vascular plants can thus be attributed to the forest flora as long as the light conditions are sufficient. Central European forests also contain several hundred moss, liverwort, lichen and algae species, which live on tree bark, dead wood or the soil.

4.2  The Geographic Distribution of Forest Vegetation 4.2.1  Zonal, Extrazonal and Azonal Forest Vegetation Potential Natural Vegetation  Central Europe would, as mentioned earlier, naturally be largely covered by forest. Instead, today around 70 % of the surface area supports non-forest transformation systems. Only around a third is still covered by forest, which is all influenced to a greater or lesser extent by human activity. We will start our look at Central European forests with the most natural forest communities, as these provide the clearest picture of the responses of the vegetation to the abiotic conditions. We will try in each case to paint a picture of the current ‘potential natural’ state of the vegetation, i.e., ‘the species assemblage that would form under the current environmental conditions if all human influences ceased, and given sufficient time to develop into its climax state’ (Tüxen 1956). A discussion of the c­ oncept © Springer International Publishing Switzerland 2017 C. Leuschner, H. Ellenberg, Ecology of Central European Forests, DOI 10.1007/978-3-319-43042-3_4

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of potential natural vegetation (PNV) can be found in Kowarik (1987), Härdtle (1995a) and Leuschner (1999b). Starting from this perspective will best enable us to understand the much more diverse mosaic of natural, semi-natural and anthropogenic forest vegetation. Numerous large- and small-scale maps of PNV have been published, for ­example of Germany (e.g. Bohn 1981; see also Scamoni 1964; Trautmann 1966; Schmidt et al. 2002; Hofmann and Pommer 2005; Kiphuth and Weinauge 2005), Switzerland (Hegg et al. 1993), Austria (Wagner 1971), Poland (Matuszkiewicz 1984) as well as other countries and regions (e.g. Kuhn 1967: Zurich area; Burrichter 1973: Westphalian Bay; Härdtle 1989: Schleswig). The potential natural vegetation of Lower Austria based on the map of Wagner (1972) is shown in Fig. 4.1, clearly illustrating the influence of relief, climate and geology on the vegetation mosaic in the eastern edge of the Alps. A map of the natural vegetation of Central Europe (Bohn and Neuhäusl 2000/2003) at a scale of 1:2500 000 is shown in Map 1.6 in Sect. 1.1. Zonal and Extrazonal Vegetation  The climax vegetation of an area can vary widely depending on the local climatic and edaphic conditions. Soils that are neither strongly influenced by groundwater nor flooded, and do not have any other extreme characteristics (e.g. lack of essential nutrients), support a vegetation representative for the regional climate. This is described as zonal vegetation, or a ‘climatic climax community’ (the Greek word climax means ladder, or last step of a ladder). The effects of the regional climate are modulated by local conditions, particularly by relief. On south to west facing slopes, plant communities develop that need more warmth and tolerate more drought than the zonal vegetation (see Fig. 4.2). Generally, these are species combinations that are characteristic for vegetation zones directly to the south or southeast. Their occurrence in Central Europe is therefore termed extrazonal. The same goes for locally cooler climates with a degree of boreal (northern) influence on the species assemblage. Vegetation maps (such as in Figs. 1.1 and 4.1) cannot show these fine grain variations in plant communities, or unusual communities caused by soil types. Azonal Vegetation  Zonal vegetation cannot establish on floodplains or on wet soils, as its typical species generally do not grow well here. Instead, climax communities known as azonal vegetation form, i.e. assemblages that occur in more or less the same form in multiple zones with differing climatic conditions, as they are influenced mainly by the same extreme edaphic factors. These are not, however, insensitive to the regional climate and will change according to it, but less strongly and obviously than the zonal vegetation. The natural vegetation of water bodies, dunes, cliff faces and other special habitats is also usually azonal. All landscapes are a mosaic of zonal, extrazonal and azonal plant communities, which is best characterised by the generally dominant zonal vegetation. It used to even be thought that azonal and extrazonal communities were just an intermediate stage towards the zonal vegetation. This ‘monoclimax theory’, originally proposed by Clements (1916), has now been disproven. For example, the silting up of a lake (see Sects. 9.3.2 in this volume, and 3.7.2 in Volume II) does not result in an oak or

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Fig. 4.1  The current potential natural vegetation of Lower Austria (Modified from a colour map by Wagner (1971), at a scale of roughly 1:2 million. The higher the altitude, the darker the symbol. Forest of different types would naturally dominate almost the whole area)

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Fig. 4.2  The dominant tree species in the zonal, extrazonal and azonal vegetation from the lowlands to the alpine timber line in western (suboceanic) and eastern (mostly continental) Central Europe. (A more detailed description is given in the text). Ol oligotrophic, mes mesotrophic, eu eutrophic. Parent rock/soil: S sand, L loam, C calcareous (limestone). moP Pinus mugo, mouP Pinus uncinata, oakw. oakwood

beech forest, even if this is the dominant vegetation on the mineral soils around the lake, but remains as an alder swamp forest (or carr; see Fig. 4.3). This vegetation is not able to build up the surface of the soil over the level of the groundwater, and is replaced by the less water-tolerant zonal vegetation only if the water table drops, i.e. a change in local conditions not caused by developments in the vegetation itself. Multiple Climax Communities  It has been recognised for at least 100 years now that even zonal vegetation is not a single homogenous climax stage, but rather a collection of floristically and structurally different communities. Their development follows different trajectories from the very beginning, depending on whether they grow on deep loam soils (e.g. on moraines or loess), on carbonate rock (e.g. almost pure limestone or dolomite) or on quartz-rich substrates (e.g. on sandstone or diluvial sand). Bedrock types containing significant amounts of silicate (e.g. granite, gneiss, basalt and crystalline schist) weather and develop into similar habitats to e.g. glacial moraines. Silicate rock or deep loamy deposits produce loamy Cambisols or Luvisols. Carbonate rocks produce humus- and later clay-rich Rendzina and Terra fusca, and quartz-rich but silicate-poor sands and sandstones develop into dystric or spodo-dystric Cambisols with a granular texture. Clay-rich rocks and marls also undergo a characteristic development, namely to Vertic Cambisols (Pelosols); however, these are relatively rare in Central Europe (Rehfuess 1990).

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Fig. 4.3  Limit of forest growth due to high soil moisture and anoxia next to a eutrophic lake. Adapted from Ellenberg (1966). Through the formation of gyttja (organic mud) or peat, the shoreline plants gradually cause the terrestrialisation of the lake. The black alder at the edge of the water line encroaches as the sediment builds up. No peat is formed outside of the flooding zone, therefore the alder swamp forest represents the end stage of the terrestrialisation process. The adjacent mineral soils support various forest communities depending on the duration of groundwater influence. Alder-ash forest turns into oak-hornbeam and mixed beech forest. (The depth of the substrate layers in the water zone has been exaggerated in the cross-section)

The differences in the natural development of the soil correspond with those in the vegetation. If multiple parent materials are present, then at least three different zonal plant communities or climax communities can develop within the same regional climate: the zonal carbonate vegetation, the zonal loam vegetation and the zonal sand vegetation. These three different vegetation types together form the overall zonal vegetation. Borrowing from Tüxen and Diemont’s (1937) idea of a ‘climax group’, we can speak here of a ‘zonal vegetation group’ which is congruent with the polyclimax theory developed by Moss (1913) and Tansley (1939). For example, in northwest Germany, there are three climax communities, namely herb-­ rich limestone beech forest (Hordelymo-Fagetum), loamy beech forest (Galio odorati-­Fagetum), and sandy beech forest (Luzulo-Fagetum; see Sects. 5.3, 5.4 and 5.5). Similarly, other areas of Central Europe support different zonal vegetation groups, not just in the lowlands, but also in each altitudinal belt (see Sect. 4.4.8).

4.2.2  The Potential Natural Vegetation of Central Europe Figure 4.2 presents an overview of the potential natural vegetation of Central Europe, including the zonal, extrazonal, and azonal vegetation. The main part of the figure contains a concise and intuitive characterisation of the most important habitat features. Particularly important here are the types of humus, as this single factor

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accurately describes a range of parameters related to nutrient availability (cf. Arbeitskreis Standortskartierung 2003 and Figs. 4.106 and 4.107): –– Mull consists of clay-humus complexes in crumb form and is characteristic for fertile soils with sufficient base saturation, good aeration, high biological activity, a species-rich and abundant soil macro- and mesofauna, and organic matter that is well incorporated into the mineral soil through bioturbation. –– Moder is strongly decomposed ectorganic material with moderate biological activity, predominantly of mesofauna; the organic matter is relatively poorly integrated into the mineral topsoil. It is generally highly acidic, but relatively rich in nutrients (particularly nitrogen). –– Mor humus is poorly decomposed humus material with low biological activity, often predominantly of fungi. Mor humus is colonised by only a few species of higher plants but many moss species. –– Swamp peat consists, like all other types of peat, of almost pure organic material; it is periodically flooded and poorly aerated, but nutritionally similar in many respects to mull, in particular in alder swamps. –– Fen peat is wetter, but similarly nutrient-rich. –– Raised bog peat is extremely acidic, nutrient-poor and almost anoxic, therefore the least inhabitable of the humus forms.

4.2.3  Altitudinal Belts of Forest Vegetation Figure 4.2 provides an overview of how the mosaic of zonal, extrazonal and azonal vegetation changes with elevation by describing the (assumed) naturally dominant tree species. As the zonal vegetation in each altitudinal belt changes with the degree of continentality of the climate, the southwestern (top part of Fig. 4.2) and the eastern (bottom) regions of Central Europe are displayed separately. In both regions, at least four altitudinal belts can be distinguished (see also Figs. 1.1, 1.6, 4.49a and 4.49b): 1. Lowlands with higher average temperatures but lower precipitation than in upland and mountain regions generally support beech and oak, or pine in areas with sandy soils and continental climates or acidic swamp forest. This is generally the case for plains, i.e. mostly flat areas in which extrazonal vegetation can rarely establish. In contrast, hilly lowland (colline) areas provide a range of opportunities for the development of extrazonal plant communities. These support either species-rich mixed oak forests with many submediterranean species, or communities of continental species, which are usually also rich in oaks. 2. The submontane to montane belt begins in the north of Central Europe as low as 200–300 m a.s.l. Its forest vegetation is usually rich in beech, even in the east of Central Europe, as long as it is still within the range of Fagus sylvatica. 3. The montane climate and vegetation begins at the point where the average temperature is at least 3 °C lower than in the lowlands, but the nightly descent of

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cold air leads to a temperature inversion, and therefore a lower risk of frost. The lower limit of this belt is between around 500 m a.s.l. in the north, and 900 m in the south. Beech remains dominant in the zonal and extrazonal vegetation here, but mixes more with conifer species than in the submontane belt. The azonal habitats here are clearly different to those in the two lower belts. In floodplains, the oak and white willow of the lowlands are replaced by grey alder. In forests with mesotrophic to eutrophic peat soils, coniferous species occur instead of black alder. The upper part of the montane belt is more frequently covered by cloud than the areas above and below it, and can be characterised as oreal (upper montane). 4 . The subalpine belt is characterised by an increasingly unfavourable climate for the majority of tree species, and for forest in general. Its upper limit is marked by the tree line, which will be discussed in Sect. 5.4.5 in Volume II. Broadleaved trees (mostly beech) are only found in the subalpine belt on the best soils and in relatively oceanic regional climates (see Figs. 4.49a and 4.49b). The montane and subalpine belts contain relatively few flat areas on which zonal vegetation could develop, and extrazonal communities or variations of the zonal vegetation adapted to the local climate are much more frequent. This inspired Tüxen and Diemont (1937) to talk of a ‘cluster’ of zonal communities (or a ‘climax cluster’). Examples of such small-scale mosaics of potential natural vegetation induced by local climate variation are shown in Fig. 5.23 for a (theoretical) mountain top with calcareous and non-calcareous rock. Despite this local variation, each vegetation belt has certain characteristics that are present throughout and are particularly visible in the tree species assemblages. As these are key to understanding the forest vegetation of Central Europe, we will go into their development in more detail in the following. We will first concentrate on the broadleaved forests of the submontane belt in western Central Europe, mainly because a large number of ecological studies from this region are available.

4.2.4  Water and Temperature Limitations of Forest Growth Forests would, in the potential natural vegetation, cover a much larger area of Central Europe below the climatic timber line than they do currently. Nevertheless, even the forest has natural limits, beyond which it cannot grow (see also Knapp 1979/1980). The most obvious ecological barrier, of which many examples exist even in Central Europe’s managed woodlands, is the moisture content of the soil (see Fig. 4.3). Limited flooding tolerance restricts the occurrence of many tree species in lowland areas with high groundwater levels, because the soil becomes partially anoxic (see Sect. 9.2.4). Forest also reaches its drought limit in places, despite the humid climate characteristic for Central Europe. This occurs when a soil layer over solid rock is too shal-

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Fig. 4.4  Drought can limit forest growth even in the permanently humid climate of Central Europe, as the soil layer over the bedrock is unable to store enough water for trees to survive occasional dry periods. Modified from Ellenberg (1966). Beech forests require more than 20 cm of soil, whereas mixed oak forests are less demanding. The transition zone between forest and the (almost) bare rock is formed by a belt of shrubs, and then of herbaceous plants (the soil depth is drawn 10× the actual relative depth). A closed sward cannot develop on bare rock

low to store sufficient quantities of water (see Fig. 4.4). This dries out completely during occasional periods of drought, and even in wetter periods, the water supply varies so widely that trees cannot grow. The drought limit, like the flooding limit, is therefore caused by edaphic rather than climatic factors. Areas of shallow soils hostile to forest growth are usually fairly limited in size in Central Europe, and surrounded by low shrubs and scrubland that, due to the lack of water, often turn yellow several weeks earlier than the forests on deeper soils. In the east and south of Central Europe, areas at the forest drought limit are generally not inhabited by beech, but instead by sessile oak (Quercus petraea, see Fig. 4.5), downy oak (Qu. pubescens) or pine. This is usually Scots pine (Pinus sylvestris) or the (according to Künstle and Mitscherlich 1975) even more drought-resistant black pine (Pinus nigra). In the western Alps, mainly on limestone, mountain pine (Pinus uncinata) is also found at the drought limit. Nearly all natural forest limits in Central Europe, whether caused by cold, drought or excess water, are dominated by a single tree species. The examples described above show that it is the other environmental factors that determine which species becomes dominant. It is at the limits of survival that the variety in reactions of these species to combinations of environmental factors is displayed most clearly.

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Fig. 4.5  Drought limit of tree growth on shallow limestone soil in the Werra uplands (near Heiligenstadt, central Germany). The zonal beech forest is replaced by Quercus petraea and Pinus sylvestris and patches of dry grassland vegetation which probably has natural strongholds at these locations

4.3  E  nvironmental Conditions and Forest Habitat Classification 4.3.1  The Climate of the Forest Interior Radiation Regime  Over half of the incoming radiation is absorbed by the upper 3–5 m of the canopy of a forest, which also contains the greatest leaf area density (Elias et al. 1989; see Fig. 4.12). In summer, closed-canopy temperate forests allow only 4–9 % of the total radiation and around 1–5 % of the photosynthetically active radiation (PAR) through to the forest floor. Beech, lime and hornbeam forests are particularly dark, with a typical PAR transmittance of only 1–3 % (see Fig. 4.6; cf. Walter 1960). This is equivalent to an average photosynthetic photon flux density of 2–10 μmol photons m−2 s−1 in mid summer (see Fig. 4.7; cf. Ehrhardt 1988; Mayer et al. 2002). In closed-canopy spruce and fir forests, around 1.5–4 % of PAR reaches the ground (Walter 1968). Oak-rich hornbeam forests are lighter, as well as oak, birch, poplar and pine forests, which have transmittance values of 5–20 % (see Fig.  4.6). Dense young stands are particularly dark, regardless of the species (Mitscherlich 1940; Eber 1972; see Fig. 5.32).

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Fig. 4.6  Relative intensity of photosynthetically active radiation (PAR) (in percent of above-­ canopy flux density) on the forest floor under single-species stands of six tree species, displayed as box and whisker plots (mean, median, 25 % and 75 % quartiles, extreme values; n = number of measurements in two stands per species; measurements taken at midday under cloudy conditions) (From Hagemeier 2002)

Fig. 4.7  Daily averages of PAR flux density (absolute values: left y-axis; values relative to above-­ canopy radiation: right y-axis), air temperature (Ta) and vapour pressure deficit (VPD) on the forest floor of a limestone beech forest near Göttingen in the growing season of 1982 (From Kriebitzsch (1989, and unpublished data))

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The majority of these numbers are averages for cloudy days and refer to mostly closed-canopy cohort stands without gaps. Much more light can reach the ground when sun-flecks created by holes in the canopy wander across the forest floor (see Sect. 4.5.2.3). The radiation in such a sun-fleck can reach up to 80 % of that in open areas, but only temporarily. Higher light conditions are also created when the canopy is not completely closed, as occurs during the senescence or the regeneration phases of old-growth forests or after forest management interventions. In these stands, the light levels on the forest floor have a left-skewed distribution, as shown in Fig. 4.8 for a young birch-pine pioneer forest in the Lüneburg Heath (Lower Saxony). In spring, the undergrowth starts to grow several weeks before the leaf flush of the deciduous broadleaved trees (Fig. 4.9). In this way, the ground vegetation exploits the higher light and temperature conditions than are available during the summer, and some plants can even make use of the period during autumn and winter, when radiation is reduced by only about 50 % (see Fig. 4.7). In the evergreen conifer forests, in contrast, the shading changes only with the position of the sun, so it is usually darker in winter than in summer. As a result, broadleaved forests are generally rich in spring-flowering plants, and coniferous forests in summer-­ flowering plants. Broadleaved and conifer forests also differ in the albedo of their canopies: broadleaved forests generally have higher values than conifers, which accordingly Fig. 4.8 Relative frequency of classes of transmitted PAR (in percent of aboveground flux density) on the forest floor under a late-­ successional beech forest (121 measurement points) and a neighbouring birch-pine pioneer forest with a partially open canopy (472 measurement points) in the Lüneburg Heath (northern Germany; width of transmission value classes: 0.5 %). The median values are 4.3 % (beech forest) and 14.0 % (birch-pine forest) (From Leuschner 1994b)

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Fig. 4.9  Limestone beech forest near Göttingen in April before the foliation of beech. At this time of the year, around 50 % of incident radiation is transmitted through the canopy to the ground, from which a dense herb layer profits

appear darker. Beech forests in leaf typically reflect around 12 % of the total radiation, whilst spruce and pine stands reflect 8 %. Reflection of the wavelengths of PAR is particularly low (Kiese 1972; Ehrhardt 1988; Leuschner 1994b; Dolman et al. 2003). An old beech forest in leaf absorbs 93–95 % of the incoming PAR, whilst for a spruce forest this is around 90 %. The forest canopy also changes the spectral composition of the radiation. On the forest floor, the PAR spectrum contains a larger proportion of dark red and infrared (DR, 700–800 nm), as well as of green radiation, but less light red radiation (LR, 600–700 nm). Whilst daylight has a LR/DR ratio of 1.15, ratios of between 0.15 and 0.97 have been measured on the forest floor (Morgan and Smith 1981). Broadleaved and conifer forests differ in their transmission spectra: the LR/DR ratio is usually very low in broadleaved forests, whilst conifer forests have a more even spectral distribution of transmitted light, with higher proportions of red and blue (see Fig. 4.10). Thermal Regime  The canopy hinders not only the transmission of radiation into the forest interior, but also the exchange of air with the atmosphere. The temperature above the soil in the forest therefore fluctuates less during the day as well as during the year than it does above open ground (see Fig. 4.11, top). The forest soil temperature remains relatively low even in the height of summer, which is of great importance for the carbon balance of the ground vegetation. The average monthly temperature within beech forests in northern Central Europe does not exceed 15 °C, even in the warmest month of the year (Schulte 1993; Leuschner 1994b). Coniferous

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Fig. 4.10  Relative spectral photon flux density beneath beech and pine forest canopies, and a wheat field (the curves have been normalised to 600 nm = 1.0) (From Tasker and Smith (1977), Federer and Tanner (1966) and Homes and Smith (1977) in Morgan and Smith (1981))

forests show an even more balanced pattern of soil temperature than broadleaved forests, the soil of which warms considerably at least once a year before the trees enfold their leaves in spring (van Eimern and Ehrhardt 1985). In contrast, the upper canopy layers can warm to 30–33 °C on still, sunny days even in relatively cool Central Europe (Aussenac and Ducrey 1977; Elias et al. 1989), making the leaves up to 3 °C warmer than the air (Schulze 1970). This warming of the canopy is particularly strong in dense young-growth stands. Nevertheless, the vertical temperature differences between the sun and the shade layers of the canopy are relatively small, and usually only a few °C (see Fig. 4.12; Baumgartner 1957; Heckert 1959; Wilmers and Ellenberg 1986). The canopy also protects the forest floor from frost. On a clear winter night in the Netherlands, Stoutjesdijk and Barkman (1992) measured temperatures of −4 °C under a Douglas fir canopy, −9 °C under (bare) larches and −13 °C under oak. An even more effective protection against frost is a layer of snow, which even at high altitudes rarely allows the soil temperature to sink below freezing. The snow layer is thinner in densely canopied conifer forests, and only around 70 % of that on open ground. New snow falling from the branches compacts the snow layer, which also has the effect that it does not start to slide as easily in sloping areas. In gaps and clearings, however, snow drifts can reach around 120 % the thickness of open areas. Due to the dense shade, the snow also remains for longer in spring. In deciduous forests, these effects are generally less strong. Water Vapour and CO2 Concentration  The stable temperature regime of the forest interior allows only small fluctuations in the air humidity (see Fig. 11.2). The stand microclimate is therefore more ‘oceanic’ in terms of temperature and humidity than that of the surrounding areas. As a result, the species composition of the ground vegetation does not as clearly reflect the continentality of the regional climate as the tree layer.

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Fig. 4.11  Daily variation in the soil temperatures in open ground and beneath various forest stands during the period of rapid warming in spring (5th–13th April 1967). From Mitscherlich and Künstle (1970). The daily fluctuations are the highest in the clear-cut area (open ground), particularly at the soil surface, but also at 10 and 30 cm depth. Beneath mixed broadleaf forest (area IV, pine-beech-­oak) before leaf flush, the temperature fluctuates more and the soil warms more rapidly than in evergreen conifer forest, particularly if this is very dense (area III, Douglas fir, slight thinning). The sequence of sites in terms of soil warming changes during the summer. From the end of October to the beginning of February, the soil in the mixed broadleaf forest remains warmer than in all other stands, including the clear-cut. This is primarily due to the isolating effect of the leaf litter layer, which is increased by the autumn leaf fall

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Fig. 4.12  Vertical profile of the leaf area density (LAI in m2 m−2 per m canopy height) (a), the PAR flux density (b) and the air temperature (c) on a clear day in July in a 25 m high oak-hornbeam forest in Slovakia (Báb Forest) (From Elias et al. 1989)

The air humidity on the forest floor is much higher than that of open ground. Even in summer, the vapour pressure deficit in beech forests exceeds 1 kPa only for short periods (Kriebitzsch 1992; Aschan and Lösch 2000; see Fig. 4.7). Much lower air humidity (vapour pressure deficits up to >3 kPa or −1.5 MPa (extractable water: white) are indicated (From Leuschner 2002b)

Fig. 4.15  Mull Rendzina on Triassic limestone (Muschelkalk), formed under a limestone beech forest (Ohm Mountains near Duderstadt, central Germany). The friable, humus-rich top soil is only 25 cm thick and contains a dense network of roots; some tree roots penetrate up to 2 m depth in cracks in the rock

small soil depth, the roots of a limestone beech forest have been shown to be able to extract water from the limestone rock up to a depth of at least 3 m (Gerke 1987). If the tree roots cannot reach additional water reserves in crevices in the rock, then the forest reaches its drought limit (see Fig. 4.4). The other hydrological extreme is

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Fig. 4.16  Schematic diagram of the relationship between soil matric potential and volumetric water content in sandy, silty and clayey soil. The conventional values are given for the permanent wilting point (PWP, −1.5 MPa = pF 4.2), the field moisture capacity (FC, −100 or −300 hPa = pF 1.8 or 2.5), and the presumed higher field moisture capacity in fine and medium sands of approximately −20 to −60 hPa (hatching to the left). Silty soils have the highest available water capacity (AWC), while that of clayey and sandy soils is lower (bars to the right of the figure, in vol. %). If the field moisture capacity of sandy soils is set higher, then the AWC increases considerably (Modified from Scheffer and Schachtschabel 2010)

experienced by forests on deep and nutrient-rich aeolian sediments, such as loess or sandy loess; here, root penetration up to depths of 2 m or more is often found (Köstler et al. 1968; Polomski and Kuhn 1998). These are the sites where the forest extends furthest towards the climatic drought limit. Plant-Available Soil Water  The permanent wilting point is conventionally set at −1.5 MPa and the field capacity of the soil at −60, −100 or −300 hPa (pF 1.8–2.5), depending on the author (Scheffer/Schachtschabel 2010). The plant-available water is defined as the difference between these two matric potential thresholds. The influence of soil particle size on the available water capacity is visible from the different water content-water potential relationships (pF curves) for sand, silt and clay depicted in Fig. 4.16. Accordingly, the highest available water capacities are found in silty soils, and the lowest in sandy soils. For diluvial deposits, it is generally the case that the higher the proportion of fine soil particles is, the higher the available water capacity (see Fig. 4.17). Glacial till therefore has a better water supply than

4.3 Environmental Conditions and Forest Habitat Classification

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Fig. 4.17  Relationship between the available water capacity of Pleistocene sandy and loamy soils and fine particle content (percentage of fine sand, silt and clay) in the subsoil (around 1 m depth). After figures in Riek and Stahr (2004) from 29 soil profiles from northeast Germany (mainly Brandenburg). The available water capacity (in mm water for the profile up to 1 m depth) was determined using laboratory desorption of soil cores (−300 hPa to −1.5 MPa). Talsands (glacial sandy deposits in depressions) are often influenced by capillary rise of groundwater (GW). The values depicted at 350 mm represent minimum values and are often higher in reality. Sands with large proportions of fine particles have a fairly high available water capacity

sand. The organic matter content also has a large influence on the water storage capacity of sandy soils (Anders 2002). Some of the widely held assumptions about the hydrology of forest soils outlined above probably need adjustment. Firstly, the trees and herbaceous species of Central European forests differ in their permanent wilting point from the widely-used conventional value of −1.5 MPa, which was determined in crop plants. Although the soil matric potential in forests with damp soils rarely drops below −0.5 MPa even in summer (see Fig. 4.18), typical hygromorphic forest floor plants frequently show signs of wilting, i.e. well above −1.5 MPa (Ellenberg 1939; see Sect. 4.5.2.5). On the other hand, young beech, oak, and ash trees can take up water even at matric potentials below −1.5 MPa (Schumann 2006), i.e. use water that is conventionally assumed to be not plant-available. The drought-sensitive spruce, in contrast, absorbs only very small amounts of water below −1.5 MPa (Rothe et al. 2002). Secondly, assumptions about field moisture capacity for sandy soils should be amended. Measurements by Flüggen (1991), Leuschner (2002b) and others have shown that fine- and medium-grained sandy soils have a larger available water capacity than was previously thought. Even in periods without rain, the soil matric potential has been found to remain in spring and early summer around −20 to −60 hPa in sandy forest soils for a long time; this water must therefore be attributed to

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Fig. 4.18  Annual fluctuation of the soil matric potential (given as soil moisture tension in bar) in the main root horizon and the occurrence of indictor plants for moisture in eleven mixed broadleaved forests in northwest Germany. Modified from Ellenberg (1939). Thick solid line: upper A horizon, thin dash-dot line: lower A horizon, dotted line: gley horizon or B horizon: dashed line: values below 1 atm., shaded areas: over 3 atm. Presence of moisture indicators: U Urtica dioica, I Impatiens noli-tangere, F Festuca gigantea, C Carex remota, A Athyrium filix-femina, V Veronica montana, Thick dots: present, with circle: thriving

the plant available water, and not to the seepage water as was previously thought (see Fig. 4.19). Many fine and medium sand soils, at least in the northwest German Pleistocene landscapes, thus have a better water supply than previously assumed. Field moisture capacities of around −30 hPa were also calculated for a beech forest on limestone Rendzina, i.e. well above the conventional −100 hPa threshold (Gerke 1987). Forest Floor Hydrology  In acidic forest habitats, a thick organic layer on top of the soil can considerably improve the water availability (Schaap 1996). A 9 cm-­ thick layer of moder with a dense network of roots in a mature oak-beech forest was

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139

Fig. 4.19  Changes in the soil water matric potential at a depth of 45 cm under stands of birch, pine, sessile oak and beech on sandy soils in the Lüneburg Heath during the growing season of 1991. Until the beginning of the dry period in mid-July, the potential was between −20 and −60 hPa even in rainless periods, i.e. considerably higher than the conventional threshold value for the field capacity (−100 hPa) (From Leuschner 1994b)

found to hold up to 40 mm of water, thereby storing around 20 % of the available water in the entire soil profile (Leuschner 1998; see Fig. 4.14). This water supplies around 35 % of the stand transpiration. Pine litter layers, in contrast, store less water and dry out more quickly in summer. Apart from forests at montane elevation and on highly acid soil, the organic layer of many other forests is relatively thin and thus contains only a few mm of water (Hölzer 1982; Fleck 1986). Influence of Tree Species  The amount of water available in the soil also depends on the tree species and the coverage of the herb layer. Deciduous trees are generally deeper rooted than coniferous trees and therefore draw more water from the subsoil; however, due to the lower interception in the leafless wintertime, the infiltration in deciduous forest soils is also higher (see Sect. 4.7.4.2). Under otherwise similar conditions, closed-canopy coniferous forests usually therefore have drier topsoils than broadleaved forests (Nihlgard 1970a; Benecke 1984; Leuschner 2002b; see Fig. 4.20). In contrast, a few authors have observed greater levels of topsoil drying for beech compared to spruce forests (e.g. Stahl 1933). In relatively open pine and larch forests, the soil moisture is determined not only by the tree layer, but also to a large extent by the water consumption of the usually dense herb layer (see Sect. 4.7.4.1). Canopy gaps, stemflow, variation in soil properties and uneven water uptake by the root system frequently cause large spatial heterogeneity in soil water storage in a stand (Gerke 1987). Herb layers can also lead to greater small-scale drying of the topsoil where plant densities are high. In a mixed oak-beech forest, soils were found to be drier under oaks than under adjacent beech trees, which was obviously caused by greater uptake of water by the roots of Quercus in dry periods (Leuschner 1993). In wetter periods, the much higher stemflow of beech is another cause of increased soil water content below beech trees.

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Fig. 4.20  Seasonal changes in the throughfall and the volumetric soil water content down to 60 cm under a beech and a spruce stand in southern Sweden (Modified from Nihlgard 1970)

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141

4.3.3  Soil Chemical Properties 4.3.3.1  Nutrient Availability Nutrient Species  Forests can be found across almost the entire soil chemical spectrum present in Central Europe; they are only absent from very boggy or saline soils, as well as some heavy metal substrates. To provide an overview of the nutrient availability in the various forest habitats, it is helpful to divide the variety of soil types into around seven to ten classes, based on the substrate type (see also Map 1.4 at the end of Chap. 1), which differ clearly in their soil chemical properties (see Table 4.1). The nutrient supply of forest soils mainly depends on the availability of the five macroelements, N, P, Mg, K and Ca. Suitable parameters for characterising the availability of these elements are the following: 1. The net nitrogen mineralisation rate is the amount of NH4+ and NO3− released by decomposers and not consumed (immobilised) by bacteria and fungi. It mirrors well the N availability for plants in all soils that are not too acidic or too cold where organic N sources play a role. Atmospheric nitrogen deposition, which is now widespread in many regions of Central Europe, and foliar N uptake must also be considered (see Sects. 3.7.2, 4.7.5.2 and 4.9.2.1). 2. The net phosphorus mineralisation rate, or alternatively a measure of the pool of plant available P. 3. The C:N, C:P and N:P ratios of the topsoil, which characterise the decomposability of the organic material and indicate a possible undersupply of N or P in the soil. 4. The pool of exchangeable Mg, K and Ca ions on the cation exchangers, as well as the total base cation pool in the organic layer, which may be available to plants in the course of decomposition. Availability of Nitrogen  Field studies estimating net N mineralisation with incubation techniques have been conducted in many Central European forests. Their results are summarised in Sects. 4.7.5.1, 5.6 and 9.6.2. Availability of Phosphorus  The plant-availability of P is more difficult to measure than that of nitrogen or basic cations, as it depends to a large extent on processes of P mobilisation by mycorrhizae and roots. Among these processes are the release of H+, the production of external phosphatases, which transform organically bound P into phosphate, and the release of oxalic acid which brings the precipitated calcium phosphate present in base-rich soils into solution (Marschner 1995). Due to the low diffusion constant of phosphate ions, the P supply to the roots is furthermore much more reliant on the porosity and water content of the soil than that of nitrate or other nutrients. As a result, the amount of P available for plant uptake depends largely on the mycorrhization, the root density and the soil physical conditions. The P availability in forest soils can be roughly estimated from the C:P ratio of the organic layer, and it differs greatly between acidic and basic soils. Whilst median

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Table 4.1  Chemical properties of forest soils in Lower Saxony, which have been assigned to seven geologically defined classes

Bedrock type Carbonate rocks Basic igneous and metamorphic rocks Carbonate rocks with surface decalcification Clay- and siltstones, greywacke Decalcified unconsolidated sediments Quartz-rich rocks Poor Pleistocene sands

Caex

Mgex

Kex

Mnex

13 1496

Corg (Mg ha−1) 183 95

(kg ha−1) 9723 1949 7668 4411

302

1825

91

6336

269

189

3551

171

10.778 2835

210

263

133

2304

107

5745

1235

148 37

331 95

274 17

2790 1289

79 91

5194 3861

1801 802

n 10 1

CECe (kmolc ha−1) 1890 596

(kg ha−1) 35.790 1018 6106 1303

446 183

101 236

26

1005

12.564 1575

647

13

482

787

147

40

389

1318

24 70

405 202

928 376

Alex

Nt

Pt

2110

From Büttner (1997b). Cation exchange capacity (CECe), exchangeable cations (Caex, Mgex, Kex, Mnex, Alex) and total store of C, N and P in the mineral soil down to a depth of 60 cm in n stands

C:P ratios between 100 and 300 are characteristic for biologically active humus forms (L and F mull), for moder layers these are between 400 and 600, and for mor humus even between 600 and 800 (von Zezschwitz 1980; Büttner 1997b; Leuschner et al. 2006b). According to these studies in central and northwest German forests, the P content of the organic material sinks rapidly with increasing acidity of the humus. It also varies between the different humus forms much more than the N content does, which is becoming increasingly homogenous across Central European forest soils due to N deposition (see Fig. 4.21). Decreasing pH values are therefore linked to a strong increase in the N:P ratio from around 60 at pH 6 to over 120 at pH 3, as shown for beech forests in the uplands of southern Lower Saxony (Leuschner et al. 2006b). This suggests that phosphorus limitation plays a role particularly in acidic (and potentially also in basic) forest soils (BMELF 1997; de Vries et al. 2000). Availability of Base Cations  Apart from in base-rich soils, the majority of Central European forest soils store only relatively small amounts of plant-available calcium, potassium and magnesium. In a nation-wide survey in the early 1990s, over 80 % of the profiles in German forest soils had topsoils (0–10 cm) with a base saturation below 20 %, i.e. less than a fifth of the cation exchange sites were occupied by Ca2+, Mg2+, K+ and Na+ (Wolff and Riek 1997). This reflects the high acidification of the majority of forest soils in Central Europe, as the base saturation sinks rapidly below pH (KCl) 4.5 (see Fig. 4.22). Considering only non-calcareous soils, at least 60 % of the forested areas have less than 400 kg ha−1 potassium, less than 800 kg ha−1 calcium and less than 200 kg ha−1 magnesium exchangeably bound in their soil

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143

Fig. 4.21  pH (KCl) and C/N and C/P ratios in the organic layer of broadleaved and coniferous forests in Lower Saxony, in relation to the humus form (median, 25 and 75 % quartiles, extreme values). For the pH value, the L/OF layer of around 120 forests was sampled, for the C/N and C/P ratios the OH layer (or the Ah horizon) of around 180 stands (Modified from Büttner 1997b)

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Fig. 4.22  Base saturation in the forest soils of Germany in the 1990s as a function of pH. Below a pH (KCl) of around 4.8, the base saturation drops steeply (From BMELF 1997)

profiles down to a depth of 60 cm (see Table 4.2). The more acidic the soil, the greater the proportion of nutrients that are bound in the organic layer. This increases the importance of organic matter decomposition over mineral weathering as the main path of nutrient supply for plant uptake. Ulrich (1994) assumed that these small and only partially available cation stocks in many acid forest soils will, in future, lead to shortages of Mg and Ca, as the replacement by weathering and deposition has not balanced the losses caused by acidification. Using the major geological soil classes, Table 4.1 demonstrates the steep gradient in the stock of basic cations from calcareous to non-calcareous soils. Quartz-rich rock types with moderate silicate content such as granite, gneiss, sandstone and phyllite are poor in plant-available Ca and Mg. However, by far the poorest soils in terms of exchangeable calcium, magnesium and potassium pools are the Pleistocene sands, which are particularly widespread in the north German and Polish lowlands. Many non-calcareous soils have low exchangeable cation pools not only because they have low base saturation, but also because of their low exchange capacity. The latter is largely dependent in sandy soils on the humus content and the degree of humification of the organic matter (Riek 1998). Increasing decomposition increases the number of charged functional groups on the organic molecules, and thereby also the cation binding sites. The nutrient content of Pleistocene sands is strongly influenced by the geological age of the deposit (Kundler 1956). The further north one goes in the eastern part of the Central European lowlands, the younger the glacial deposits and the higher the silicate content. The Weichselian sands of the Mecklenburg (Pomeranian) stage are still relatively rich in silicates, whilst the Brandenburg stage and particularly the even older Saale ice age sands are poor in silicates (see Fig. 4.23). Medium-grained sands are also usually poorer in silicate than coarse or fine-grained sands (Kundler

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Table 4.2  Percentage of soil profiles in seven classes with differing K, Ca and Mg stocks, from the German Forest Soil Inventory K Class (kg ha−1) 1600

Uplands Lowlands 14.6 30.9 47.5 36.4 20.3

12.6

8.9

12.4

5.5

3.7

1.4

1.4

1.8

2.6

Ca Class (kg ha−1) 8000

Uplands Lowlands 6.5 4.2 27.2 27.9 29.2

42.2

21.5

18.9

9.6

1.6

4.2

3.9

3.1

1.4

Mg Class (kg ha−1) 2000

Uplands Lowlands 6.6 20.6 25.2 37.8 27.5

28.6

24.4

11.1

9.7

1.8

3.9

0

2.7

0

From Wolff and Riek (1997). 818 stands on acidic soil from the lowlands and low mountain ranges (total stocks in the organic layer and exchangeable stocks in the mineral soil down to 60 cm depth)

1956). Fluvioglacial ‘talsand’, which has been transported over long distances by water, is often poorer in silicates than moraine deposits, glacial tills or meltwater sands. 4.3.3.2  Soil Liquid Phase Composition The composition of the liquid soil phase determines the chemical medium in the immediate surroundings of the roots, including the concentration of potentially toxic elements. Despite the variety of geological substrates, Central European forest soils are remarkably uniform in their acidity. According to the German Forest Soil Inventory, around 75 % of the investigated profiles have a pH (KCl) in the topsoil (10–30 cm depth) of less than 4.2, i.e. are highly to extremely acidic (see Fig. 4.24; Wolff and Riek 1998). Less than 10 % of the soils have a pH (KCl) of >6.3, and 4 % between 5.1 and 6.3. The average (median) pH is 3.89, and in the organic layer even 3.0. pH values in the topsoil above 5.1 are found today only in limestone soils, or those on diabase and basalt. In Switzerland, in contrast, where limestone is more widespread, 45 % of the forest soils surveyed in 2000 had a pH >4.6 (BUWAL 2005). The chemical composition of the soil liquid phase undergoes strong temporal fluctuations. These are caused by the varying activity of microorganisms and roots, and the changes in temperature and moisture. As shown in Fig. 4.25 using the example of pH values, the H+ ion concentration of the liquid soil phase can change up to ten-fold throughout the course of a year. The curves of the various forest stands in the figure do not run parallel, but show similar seasonal trends. The same is true of the concentrations of nitrate and ammonium, which are mainly determined by the

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Fig. 4.23  Silicate content of sandy soils from various glacial periods in the northeast German lowlands. Modified from Kundler (1956). The older the Pleistocene sand, the poorer it is in silicate. The silicate score is a relative value that was determined by visual inspection of the particles through a microscope

Fig. 4.24  Frequency of pH (KCl) values in 1751 forest stands in Germany, which were surveyed for the soil inventory at the beginning of the 1990s (topsoil at 10–30 cm depth) (Modified from Wolff and Riek 1998)

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Fig. 4.25  Monthly fluctuation (in 1937) in the acidity (pH (H2O)) in the topsoil of multiple birchoak forests (above the dotted line) and herb-poor oak-­hornbeam forests. The curves for herb-rich oak-hornbeam forests cannot be displayed as H+ concentrations, as they are found in the cross hatched area of the diagram, and sometimes in the diagonally hatched area (Modified from Ellenberg 1939)

interplay of mineralisation, nitrification and biotic uptake. A period of high nitrification and associated H+ production is often followed by increased nitrate, aluminium and sulphate concentrations in the soil solution, which are then leached out of the soil profile (e.g. Ulrich 1994; Kölling et al. 1996). Table 4.3 compares the average ion composition of the liquid soil phase in acid and basic soils. Acidic soils have higher concentrations of not only H+ and Al3+, but also of Fe2+, Mn2+ and usually also of H2PO4−. 4.3.3.3  Concentrations and Stores of Carbon and Nitrogen Soil Organic Carbon  According to the calculations of Burschel et al. (1993) and Ulrich and Puhe (1994), the forests of Germany store on average around 227 Mg C ha−1, of which around 60 % is contained in the soil (around 135 Mg C ha−1). Somewhat smaller median pools of soil organic carbon (SOC) were found by Wolff and Riek (1997) in the German Forest Soil Inventory (99 Mg C ha−1 in the mineral soil from 0 to 90 cm and the organic layer). Baritz (1998) gives a mean of 108 Mg C ha-1 for the forest area of Germany (organic layer and mineral soil to 90 cm). At the regional level, the greatest influence on soil carbon storage is exerted by the elevation, through its effects on both temperature and soil moisture. The soil carbon store in Lower Saxony more than doubles between sea level and 700 m (Büttner

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Table 4.3  Differences in the composition of the soil solution in non-forested limestone and silicate soils in southern Sweden (in μmol l−1; the samples were extracted from moist soil by high speed centrifugation)

pH Ca2+ Fe2+/Fe3+ Mn2+ Al3+ Al(OH)4– HCO3− HPO42− H2PO4−

Calcareous soil 7.5–8.5 2000–3000