An Investigation on the stem elongation of two chaparral species

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AN INVESTIGATION ON THE STEM ELONGATION OF TWO CHAPARRAL SPECIES

A Thesis Presented to the Faculty of the Department of Botany University of Southern California

In Partial Fulfillment of the Requirements for the Degree Master of Arts

hy Edward Carmack Butts June 1942

UMI Number: EP69868

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UMT D is s e rta tio n P u b lis h in g

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T h i s thesis, w r i t t e n by

ED¥M2...aAHMA0K.. BUTTS.......... u n d e r the d i r e c t i o n o f h . X s F a c u l t y C o m m i t t e e , a n d a p p r o v e d by a l l it s m e m b e r s , has been pr esen ted to a n d acc ep ted by the C o u n c i l on G r a d u a t e S t u d y a n d Re se ar ch in p a r t i a l f u l f i l l ­ m e n t o f the r e q u ir e m e n t s f o r the degree o f

...... m . S T m . . O F . M T S .................

D ean

Secretary D a te....

Jnna,...19.42

F a c u lty Com m ittee

Cbm rm an

TABLE OF CONTENTS CHAPTER

I.

PAGE

I N T R O D U C T I O N .....................................

1

Review of the literature • . « .................

3

THE INVESTIGATIVE A R E A ..................

6

General features

6

Location of the a r e a ..........................

7

A i m s ......................................... . II.

12

The v e g e t a t i o n .................................

14

............................

Northerly s t a t i o n ..........

19 22

Riparian station . . .

. . . . .

Live oak woodland station

25 28

EXPERIMENTAL RESULTS .............................

31

Evaporation

31

Ceanothus stem e l o n g a t i o n ....................

37

Soil moisture and r a i n f a l l ....................

43

Stem elongation and soil temperatures

53

Stem decrement IV.

11

THE INSTRUMENTAL S I T E S ...........................

Southerly station

III.

.

. . . .

...............

62

S U M M A R Y ..........................................

73

Southerly s t a t i o n ............................

73

Northerly station

75

Riparian station .

. . . . . . . ..........

77

iii CHAPTER

PAGE Live oak woodland s t a t i o n .....................

V.

C O N C L U S I O N S ........................

BIBLIOGRAPHY

.......................................

79 82 85

LIST OF FIGURES FIGURE 1.

PAGE

Evaporation and stem elongation, southerly station

2.

34

Evaporation and stem elongation, northerly station

3*

36

Evaporation and stem elongation, riparian s t a t i o n .................................. . . . .

4.

39

Evaporation and stem elongation, live oak wood­ land station

..................

41

5.

Soil

moisture and rainfall, southerly station

. .

45

6.

Soil

moisture and rainfall, northerly station

. .

47

7.

Soil

moisture and rainfall, riparian station

. .

49

8.

Soil

moisture and rainfall, live oak woodland

station ......... 9.

•

. . . . . . . .

Stem elongation and soil temperatures, southerly s t a t i o n ...................

10.

.............

56

Stem elongation and soil temperatures, riparian station . • • • • • . • •

12.

54

Stem elongation and soil temperatures, northerly station

11.

51

...........

• • • • •

60

Stem elongation and soil temperatures, live oak woodland station

. . . . . . . . . .

13.

Stem decrement,

the southerly station

.........

14.

Stem decrement,

the northerly s t a t i o n ............

61 64 66

FIGURE 15.

PAGE

Stem decrement, the riparian station . . . . . .

69

16.

Stem decrement, the live oak woodland station

.

71

17.

Interrelations

of factors, southerly station .

♦

74

18.

Interrelations

of factors, northerly station .

.

76

19.

Interrelations

of factors, riparian station

.

78

20.

Interrelations

of factors, live oak woodland

station • • • • • • . . .

.............

.

...

81

LIST OF TABLES

TABLE

PAGE

1.

Woody plant species at the s t a t i o n s ............

17

2.

Ecological factors affecting the stations

18

3.

Influence of evaporation and soil moisture on stem elongation

...

. . . « • • • • , ...........

. . . .................

40

4.

Rainfall

5.

Monthly rainfall data . • • • • • • • • . . . .

50

6.

Influence of soil moistures on stem elongation

55

7.

Influence of soil temperatures on stem elongation

...............

48

. . . . . . . . .

8.

Stem elongations

.........

58

9.

Soil temperatures and stem e l o n g a t i o n .........

62

Stem decrement and correlated factors

68

10.

• • « . . • • • • .

57

. . . . .

LIST OF ILLUSTRATIONS FIGURE

PAGE

A.

The southerly exposure

.............

B.

Instrumental site, southerly

C.

The northerly e x p o s u r e ............. .............

23

D.

Instrumental site,

northerly station . . . . . .

23

E.

The riparian plant

community . . . . . . . . . .

26

F.

Instrumental site,

riparian station

26

G.

The live oak woodland, area . • • • • • . . . . •

29

H.

Instrumental site, live

29

station . . . . . .

oak woodland

. . . . . .

. . . . . .

20 20

LIST OF CHARTS CHART

PAGE

1.

The v e g e t a t i o n ...............

2.

Plant census chart,

southerly station

3.

Plant census

chart, northerly station

4.

Plant census chart, riparian station

5.

Plant census chart, live oak woodland

15 ........

21

. . . . .

24

. station

.

27 30

LIST OF MAPS MAP

PAGE

1.

Southern California mountains

..................

2.

Santa Monica Mountains

..............

8

3.

Topographic map of investigative a r e a ...........

10

4.

Instrumental sites

13

. . . . .

2

AN INVESTIGATION ON THE STEM ELONGATION OF TWO CHAPARRAL SPECIES INTRODUCTION The number of ecological factors regulating stem growth of chaparral species is not definitely known.

Undoubtedly,

the total is larger than now suspected for climatic fluctuations are never the same from season to season.

Hourly variations of

environmental conditions may be very significant. The contents of this paper deal with certain specific conditions regulating stem elongation.

They are; rainfall,

evaporation, soil moisture, soil temperature, the water-holding capacity of soil, and maximum and minimum air temperature.

It

is thought that the results obtained by this combination of investigative possibilities will give additional clues regard­ ing normal stem elongation. Four distinct plant communities within a radius of 300 meters were chosen for intensive instrumental investigations. Weekly readings, without interruptions, were made at these sites from November 2, 1S41 to May 3, 1942.

This period includes

a part of the so-called autumn growth and the greater portion of the rainy season when most of the chaparral stem elongation occurs.

The Santa Monica Mountains have been investigated in

many localities but, so far as the writer could ascertain, the particular area of the present investigation has not been used.

MRP

OF

SOUTHERN

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MTi K fiH m S S

5 Review of the Literature The first studies of the chaparral were made from the viewpoints of geography, taxonomy, and forestry.

Among the

early European botanists who described the vegetation of western North America, the investigation

of Schimper

(1905)

was the first to be at all satisfactory.

McKenney (1901)

discussed chaparral nsuccessionfl in the Santa Monica Mountains, California.

Lieborg

(1899, 1900) described the chaparral of

certain United States forest reserves.

Minor articles by the

United States Forest Service and independent taxonomists were published prior to 1920 but are difficult to locate.

These

early papers were broad in scope because instrumentation was not generally employed. Early California botanists were mainly concerned with reports of taxonomic significance. chaparral of Mt. San Jacinto.

Hall (1905) studied the

Parish (1905) published articles

relating to the chaparral of southern California. has also written an excellent account of this area.

Clements These early

attempts, without scientific instrumentation, y/ere rather superficial studies.

Most of these papers were observational

and general rather than specific in character. The first careful and detailed investigation was by Cooper (1922).

He compiled a great amount of instrumental

data, thereby opening this aspect of the problem to further study.

While his interpretation of the whole was from a

4 series of local experiments, the fact remains that his work was the forerunner of similar studies.

Shreve (1927) published

results of careful experiments in the Santa Lucia Mountains. Shapiro and de Forest

(1932) reported the results of trans-

pirational studies in the Santa Monica Mountains. Edaphic factors, other than soil moisture and temper­ ature, have not been fully worked.

Oster

(1934) has exper­

imented and written regarding soil alkalinity and salinity. This field is not fully understood and needs further study. Soil temperatures were studied by Bauer (1935).

possibly the best detailed expositions on soil moisture

are: Shapiro (1936).

(1934) and Watkins

(1931), Cook (1932), Crosby (1936), and Shreve

The physiographic features, such as slope, exposure,

and range have been rather extensively studied.

Among the

contributors in this field Shreve (1915), Cooper

(1922), Oster

(1924), Bauer

(1928, 1934), Watkins (1935), and Simpson (1936)

have left reliable accounts. The taxonomic and floristic field has been carefully worked for many years. Hall (1902), Abrams 1934), and Munz

Among a host of reliable writers are:

(1910, 1917), Jepson (1925), Bauer

(1935).

(1928,

Hall left a fine account of the Mt.

San Jacinto region while Bauer worked the Tehachapi and Santa Monica Mountain areas.

Jepson, Abrams, and Munz covered large

chaparral areas in the state of California.

Leaf structure and

variation have been the subject of many investigations.

Cheng

5 (1940) studied leaf structure in the Santa Monica Mountains, and at the present time is investigating the leaves of California species of Adenostoma. and Remple

Shapiro (1931), Cook (1932),

(1936) have contributed information on transpiration.

Possibly the most difficult field of chaparral develop­ ment to investigate is root growth and extent.

The rocky sub­

stratum is a barrier to extensive excavation, which v/ould give the answer to root growth.

Bauer

(1934) has done some work in

this respect but this aspect of scrub growth needs more in­ vestigation.

Other fields of which little is known are the

effects of dew, frost, and snow on the natural development of chaparral.

Bauer

(19B8) contributes some information regard­

ing snov/ and frost as factors of scrub growth. The most intensive work on southern California chaparral has come through the botany department of the University of Southern California during the last fifteen years.

Graduate

students under the guidance of Dr. Howard de Forest have contributed much valuable material regarding normal chaparral development and significance.

Results of these experiments

and investigations are available in the library of the University of Southern California.

I.

THE INVESTIGATIVE AREA General Features

Chaparral is the principal vegetation at lower altitudes on most southern California mountains.

It covers hills near

sea-level and develops extensively up to about five thousand feet, although it may range higher or lower in some instances. Such factors as fire, grazing, or logging may materially affect the extension of chaparral. The Santa Monica Mountains offer a good example of southern California chaparral growth.

Their topography is such

that almost every exposure is represented. a network of drainage patterns. steep and rocky.

The canyons present

Their bordering slopes are

Such topography, with rainfall coming during

one season, gives maximum play to erosive elements.

Mild wet

winters, followed by dry hot summers, give to these mountains a distinctive Mediterranean type of climate.

The vegetation

is mostly broad-sclerophyll and shrubby in nature.

Occasional

areas of dark green, live oak woodland interrupt the grey green of the scrub. While fires have been of frequent occurrence, no recent evidence of such disturbance was noted near the experimental stations.

This particular section of the Santa Monica Mountains

is privately owned and fenced, thus affording stability to the plant life.

Biotieally the area is suited for experimentation,

7 as the disturbing factors of grazing and trespassing are materially lessened. Location of the Area The Santa Monica Mountains of southern California are one of the outer coastal ranges.

The range extends westward

from the city of Los Angeles about thirty miles.

The axis of

these mountains is about 34°5 * north latitude and its center is near 118°40» west longitude.

Map l,page 2 shows the general

position relative to other southern California mountain systems. The trend is in general east-west, which is a prominent feature of many ranges in California south of Point Concepcion. A rough topography is the rule, with steep slopes exposed to almost any point of the compass.

The chief geologic

formations are of middle and upper Miocene.

All these layers

have been badly indurated and metamorphosed elevation.

Most of the soils are classified

(Hoots 1930) during (Nelson 182 0}

as lIrough, broken, and stony; numerous rocky points are common.” A layer of fine soil, mixed with gravel, has attained some depth in places.

Such a condition is not of common occurrence

due to steep slopes and sudden rains.

Deep and lasting acumu­

lation of soils is not the rule. The location of the investigated area is near Sepulveda Boulevard, four miles north of its junction with Sunset Boulevard. Generally Sepulveda Boulevard crosses the Santa Monica Mountains

8

S / I N T H

M O N I C A

M O U N T A I N S

SHOWING S O M E OF THE CANYONS, GENERAL TOPOGRAPHY, A N D OR A I N AGE TRENDS. L O C A TIO N O F T H E E X P E R IM E N T A L A R E A IS IN D IC A T E D 3 1 THE A STEH ISM %

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28 Live Oak Woodland Station The woodland site was representative of live oak areas so common in the chaparral of southern California* Such groves of Quercus agrifolia commonly grow on the alluvial benches of most coastal southern California mountains. The vegetation, while covering ninety percent of the areal surface, was high and always allowed a comparatively good air circulation.

This fact somewhat speeded evaporation, which

was greater than seemed possible at first examination. The exposure was N. 45° W. and on a slope of twenty percent.

Storms and rains blowing up Sepulveda Canyon, struck

directly upon this station.

This condition accounts for the

fact that, despite the dense canopy of foliage, the site consistently showed a high percentage of soil moisture at the level of thirty centimeters.

The dense live oaks shade the

area, so that only diffused light strikes the soil. soils were covered with a thick coat of leaves.

Surface

This litter

was accumulated to depths of three to four inches, and apparently it does not decay readily, thereby protecting the soil from rapid v/ater loss. This community of live oaks grew on an alluvial slope directly across Sepulveda Creek from Sepulveda Boulevard. Despite the proximity of this site to possible biotic effects, the actual experimental area was undisturbed during the course of the investigation.

29

Fig. G. The live oak woodland area. A typical scene in the Santa Monica Mountains. Location of the instruments was near the middle of the scene. Photographed about three P.M. January 5, 1942.

: -V;

Fig. H. Close view of the instrumental site. The dense shade generally prohibited many species from thriving at this situation. Photographed about noon, January 7, 1942.

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40 flowers.

The remaining stems, with two exceptions, all

flowered, after which stem elongation was inhibited for periods of from ten to thirty days.

The wisdom of marking stems, from

various parts of the plant is apparent.

An average of four

such stems should be indicative of growth tendencies among the various stems of a species. There are indications that high evaporation rates prom­ ote stem elongation provided other factors are not limiting. This may even be true of extremely high evaporation rates if soil moistures are sufficiently high. Table 3. Comparison of high weekly evaporation rate with stem elongation and soil moistures. Southerly station Evaporation per week. cc.

Total weekly stem elongation, cc.

Date

Soil moisture at 30 cm. Percent

281

Nov.

9

0.5

3.4

274

Mar. 29

3.1

6.7

250

o CO + > o S3

0.1

5.4

227

Mar.

8

1.5

7.e

225

May

3

0.7

7.2

223

Feb. 15

3,2

7.0

200

Nov. 16

0.2

1.0

Northerly station CO CO CV2

Nov. 30

0.2

5.0

225

Feb. 15

2.7

14.6

221

Nov.

9

0.5

12.6

207

Mar. 29

4.6

13.7

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48 results obtained.

At this favorable situation, only once

did the soil moisture rise above the saturation point. This was for the week of April 12 and the reading came from a soil sample taken during a rainstorm.

The water

content at the 30 cm. level taken at the same time was far below field capacity.

(Fig. 8.)

At the northerly station, where environmental condi­ tions tend to conserve moisture, the same conditions pre­ vailed.

Soil moisture percentages (Fig. 6), at the 10 cm.

level, came very close to moisture capacity for the weeks of March 15 and April 12. capacity.

Two other weeks approached

They were February 22 and January 25.

Soil moisture conditions thus were not very high at any time from November 2, 1941, to May 3, 1942.

Table

3, page 50, shows normal rainfall for this period. Table 4. Total rainfall for the six complete months recorded during the investigation

Station

Nov. In.

Southerly

.22

3.73

3.84

2.06

1.72

4.28

Northerly

.22

3.72

4.10

1.95

1.69

4.40

Riparian

.12

2.09

1.44

1.26

H to•

2.62

3.77

3.67

2.10

1.12

-J.S3

Live oak woods

Dec. In. .

Jan. In.

Feb. _In.

Mar. In.

Apr. In.

The total rainfall for the above six months is: Southerly 15.85, northerly 16.08, Riparian 8.34, and live oak

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Stem elongation at the live oak woodland was more steady than at any of the other experimental areas.

Rhamnus

crocea stem development at the southerly station was much less than at the other stations.

A review of the total stem

elongation at the four experimental sites reveals the follow­ ing conditions: Table 9« Rhamnus and Ceanothus stem elongation; a comparison with soil temperatures. Aver, soil Temp. 30 cm. weekly F.

Aver, soil Temp 60 cm. weekly F

Station

Total stem growth cm.

Live oak woodland

20.2

51.9

52.6

Riparian

18.8

55.0

54.6

Southerly

11.4

59.9

59.9

Northerly

16.7

43.5

49.9

The total stem elongation for the entire experiment was highest at the live oak woodland site.

With the exception of

the northerly station there was less growth, as recorded above, with increase in soil temperature.

It would seem that

average soil temperatures of around 52 to 53 deg. are most conducive to stem elongation.

The truth may, however, be

otherwise, as the high soil temperatures of the southerly station (59•9 deg.) would likely, with sufficient rainfall, be more conducive to stem growth than the 52 deg. of the

63 live oak woodland.

In southern California, where rainfall

is irregularly precipitated, high soil temperatures are apt to promote excessive evaporation and thereby deplete the available water content of the soil.

The above results at

the northerly station are incomplete, as normally stem growth at such exposures continues until late in the summer. Stem Decrement During the fall and early winter months stem growth in the chaparral of southern California is possibly subjected to conditions that are somewhat different than those encoun­ tered in most other such areas in California.

The first rains

of the fall months are usually followed by rather lengthy periods during which evaporation is high, while at the same time soil moisture content is uncertain.

Early fall rains in

southern California follow no regular pattern.

This condition,

and also the hot weather, which is common late in November and even in December, causes a growth to begin in the scrub that is not always permanent.

The fall rains give only temporar­

ily favorable moisture conditions.

Any stem elongation under

such instances is highly unstable. During the course of this investigation some of the fall stem elongation dried and was lost.

Such occurrences are

referred to as stem decrement during the course of this work. Eig.. 16 gives a graphic idea of this phenomenon.

This figure

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65 shows that the greatest stem decrement occurred at times of high evaporation, high maximum air temperatures, and low soil moisture content.

The weeks ending November 9 and 30 (Fig.

16) show this condition clearly.

The rainfall during the

week ending November 2 (Fig. 18) raised soil moisture to favorable proportions, thus initiating stem elongation. However, because of high evaporation rates from November 9 to November 30, the soil moisture dropped to five and then below five percent. All stem elongation initiated during the favorable soil moisture period of November 2 was subjected to dessicating effects.

At first examination this condition should have

been more positive at the southerly station because air temp­ erature and evaporation were usually higher at that site. This was true during the spring months but not true for the fall months, when stem decrement was common at the remaining three stations.

Light November rainfall was quickly evapor­

ated at the southerly station so that there was little initi­ ated stem elongation during the month of November at that station.

Each station did, however, show stem decrement for

the week ending November 30. The light rainfall for the week of November 2 raised soil moistures somewhat, and as a result stem elongation began generally at all the stations.

This soil moisture was

rapidly evaporated during the following weeks, with the result that any stem growth was subjected to limiting factors.

The

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S T E M R E C R E M E N T NORTHERLY S T A T I O N M A X I M U M TEA* A EAR. »»»««•••« S O U M O I S T U R E STOCM. E V A P O R A T IO N ---- 1--- RNAmRUS S T E M DECREMENT ------------- SOIL M O I S T U R E 10CM ■ CEAHOTRUS S T E M R E C R E M E N T —

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67 southerly station was the only site not to lose accumulated stem elongation for the week of November 9.

A possible rea­

son for this was the fact that Rhamnus stem elongation, at the southerly station, did not begin to develop early because of unfavorable moisture conditions* Such uncertain stem elongation is likely the mile in the chaparral of the coastal mountains of southern California. The climatic conditions are such, in this particular region, that soil moisture is undoubtedly the master and limiting factor regulating most natural growth of woody perennials*

At

any time after October 1 there may come a fairly heavy rain, to be followed by low humidities and high air temperatures. Any stem elongation that might be initiated from these early rains is apt to be subjected to lowering soil moistures.

When

the soil moisture gets below five percent of dry weight, any stem elongation that may have accumulated is adversely affected. Under such conditions stem increment will wither and die.

When

this happens, any later growth will be started at the first or second node below the injured meristem. This condition was noted during the course of the in­ vestigation.

Such stem decrement is doubtless of common oc­

currence in the Santa Monica Mountains of California, and some writers believe that the formation of thorns on desert vegeta­ tion had its beginning when drying conditions might cause whole stems to die.

Subsequent growth from a lower node leaves old

dead stems projecting out as protection to later growth.

68 The table on page 68 shows the weeks of stem decre­ ment at three of the stations.

Additional data is to be

found on Figs. 17 to 20, regarding this phenomenon.

The

northerly station is not included on the table because stem decrement at that situation was insignificant.

Moisture

conditions were relatively not critical at the northerly station. Table 10. Stem decrement and correlated factors. Riparian Station Date

Decrement cm.

Weekly Evap. cc.

Air Temp. Max. F.

Soil Moisture 30 cm.Percent

9

1.1

141

89.6

*

Nov. 16

0.3

121

88.0

*

Nov. 30

1.1

162

84.0

4.8

Nov.

Live oak woodland 9

0.1

134

89.6

*

Nov. 30

0.4

169

84.0

6.9

Dec. 21

0.3

59

82.0

8.3

Nov.

Southerly Station Nov. 16

0.2

199

88.0

*

Nov. 30

0.5

250

84.0

5.4

Jan. 11

0.2

148

82.0

10.4

Feb.

1

0.5

107

76.0

6.6

Feb. 15

0.4

223

80.0

7.0

8

0.6

226

86.0

7.8

Mar.

Denotes no records available for soil moistures at the 30 cm. depth. Such readings began Nov. 30.

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70 The records for the riparian station at the top of the table show that without exception the high temperatures (Max.) were associated with stem decrement.

The evaporation

rates are lower for the riparian station, which was protected from direct rays of the sun.

(Chart No. 4 .)

able soil moisture reading was also low.

The one avail­

Fig. 15 will, how­

ever, show that the soil moisture at the 10 cm. levels for this station were low.

Undoubtedly the 30 cm. soil depth

was somewhat lower. The statistics for the live oak station, also show that low moisture content, high maximum air temperature, and high evaporation are associated with stem decrement. exception is for the week ending December 21.

The one

There was,

however, a decided drop (Fig. 20) in soil moisture from the previous week. panied by

The rainfall of December 14 to 21 was accom­

high winds, and it is possible that the decre­

ment recorded for December 21 was a wind injury. The table at the bottom of page 68, giving figures for the southerly station, is also indicative of the abovementioned trends. excessive.

Evaporation rates were so high as to be

These high rates were accompanied by

temperatures and low soil moisture content.

high air

Stem decrement

at this southerly station was not so pronounced for the fall months as the live oak woodland and riparian situations. This is understood by checking Fig. 17, and it will be noted

that after an initial stem elongation for the week ending November ^fchere was very little new stem development to be affected by limiting or destructive factors.

Simply stated,

stem elongation is not usually started by the early and light fall rains on the southerly slopes.

Conversely, stem

decrement was noted until March 4 at this station, which was long after any such evidence was found at the other three stations.

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