Convergence in Vegetation Structure in the Mediterranean

Convergence in Vegetation Structure in the Mediterranean Communities of California, Chile and South Africa Author(s): R. M. Cowling and B. M. Campbell Source: Vegetatio, Vol. 43, No. 3 (Dec. 31, 1980), pp. 191-197 Published by: Springer Stable URL: http://www.jstor.org/stable/20145836 . Accessed: 30/04/2013 06:24 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp

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IN THE MEDITERRANEAN

CONVERGENCE IN VEGETATION STRUCTURE CALIFORNIA, CHILE AND SOUTH AFRICA* RM. 1

OF

COMMUNITIES

COWLING1 & B.M. CAMPBELL2

Botany Department, University of Cape Town, Rond ebosch 7700, South Africa Botanical Research Institute, P.O. Box 471, Stellenbosch 7600, South Africa

2

Keywords: Province,

California,

Cape

Vegetation

structure

Chile,

factors,

Edaphic

Convergence,

Introduction

Mediterranean

in California

gradients

recent

the mediterranean

years,

climatic

southern California and central Chile have been the subject of

extensive

on

studies

convergence

community

the similar

along

(e.g.

In

the

are

Chile.

richness,

If community

conver

climatic

it

constraints

to show that, despite distinct floristic in

climatic

of the three

gradients

occur

structure

community

California-Chile

similar (Mooney

Species

Africa,

similar

trends

parallel

origins,

Castri & Mooney 1973, Mooney 1977, Cody & Mooney 1978). The main hypothesis is that under similar environ mental conditions similar forms will evolve, irrespective of

continents. was

substrate

comparisons

1977). Certain Cape sites have soils that the

than

poorer

nutritionally

sites

analogous

on

the

the genetic histories of the biotas involved. This has been

other continents. Thus the r?le of substrate in determining

tested

vegetation

by

structure

community

comparing similar

mentally

in

sites

environ

of

of plant

vergence

structure

community

in California

present

between ranean

study of

convergence

plant

the Cape regions

structural climatic

data gradient,

to determine

designed

structure

community

mediterranean

of California

Parsons & Moldenke

the

in

collected with

region and Chile.

data

We

Cape

collected

in the

sites

(1975) along analogous

Ms.

Four

along

by

Table

climatic

from

and

thank Mr.

for help with pre-project F.J. Kruger planning, E. Esterhuysen for aid with D.J. Parsons identifications,

for

and data, unpublished D.J. Parsons, R.K. Mooney, H.C. Taylor, R.H. Whittaker,

H.W.

H.P. Bond, P.H. Raven,

Vegetatio 43, 191-197 (1980). 0042-3106/80/0433-0191 $ 1.40. Junk B.V.

Publishers.

The Hague.

Printed

and

Chile

are

sites

of

those

(1975). Their methods were followed between

comparability

sites were

study

their

sites

in the Cape

chosen

and

to represent

sites chosen by Parsons & Moldenke 1). The

hot,

dry

sites

to cool,

parallel

moist

the

(Fig. 1,

aridity

gradient

montane

condi

maritimal,

foothill,

of

increasing

progressions temperature,

decreasing

sites,

an

along

to as desert,

The

of

montane

ranged

referred

montane.

durations

are

semi-desert

are

Sites

precipitation,

H.A. Linder, J.C. Scheepers,

Peet, and an anonymous reviewer for on the manuscript. comments This work was supported by a Biome C.S.I.R. the Fynbos post-graduate grant (R. Cowling), Institute. Environmental and the Botanical Research Project

Dr. W.

to ensure

climatic

a

tions. *We

investigated.

in the Cape.

those

compared

same way

the California

for

in order

occurred

the mediter

have at

data

Parsons & Moldenke

whether

has

and

be

Methods The

was

also

and

Chile. The

could

convergence

areas.

isolated

evolutionary

et al. (1970), Parsons & Moldenke (1975) and (1976) have demonstrated considerable con

Mooney Parsons

?

and under

should be possible

of

regions

occur

does

gence In

South

climate,

periods summer-drought on all continents is evident

and

decreasing

from (Fig.

desert

to

2). Dotted

lines in the Cape climatic diagrams indicate that climatic data Where

had

to be

specific

from

adapted rainfall

data

were

191

in The Netherlands.


nearby lacking,

climatic the mean

stations. annual

1 2 3 4

temperature desert maritimal foothill montane

each

of

component

/"ARGENTINA !

numbers PLOSANGELES CALIFORNIA

the

.-Descanso lw4? l?OcotilJa -MtLaguna

_33N

vegetation whereas

the

site were

genera

were

determined. recorded

Parsons

& Dunn

Results

Rainfall

The

at

the nearest

data,

the effect

weather

of

station

station.

corrected

by

of

distribution

Structural in three

of

desert maritimal foothill montane

below

total

in the

10 of

characters at

plots

the Cape

used

(1975)

in the field and

in mediterranean et al.

1970, Mooney

floristic

site and

between

applying

between

similarity

on

the

similarities

of on

sites

three

regions

1970).

the

normal

continents

the woody a single

show

floras

whereas

continent

only the

is much

higher (Fig. 3). The Venn diagrams (Fig. 7) further illus D-

-17 -Ma

-

40

temperature

1. The dominant Table ;ite. vegetation type of each study of Chilean and Californian sites from Mooney Descriptions In the Cape occurs on rich shale the desert vegetation (1977). coastal sands, and the soils, the coastal scrub occurs on base-rich to the Cape sands. References fynbos occurs on nutrient-poor sites are noted

selection

sites

analogous

that occurred

In the case difference

altitudinal

was

annual

the distribution

from

weather

the

and

Series)

estimated

The

families

sites.

rainfall was read from isohyet maps (1 :250 000 Average was

located the woody

similarity

slight

rainfall

and

and discussion

Floristic

Annual

were

sampled. and

& Moldenke

environmental

(Mooney

of the study

site

structural

reflect

1. Location

elevation

1 ha. Only

was

vegetation species,

100 m2

ke (1975) as they are easily measured

Fig.

of

between

10 plots. of the Cape sites suggested that uniformity further was not required. The structural charac sampling ters recorded leaf size, leaf duration and form, growth were for chosen Parsons Molden & spinescence study by sites,

The

MEXICO

distance

25 km.

of woody

of each

plots

?C per m

0.0064

10 plots of site, Cape in a homogenous area of

randomly \CHILE

was

station

At

of

Maximum

1969).

weather

rate

lapse

(Strahler

00

.05

CALIF

D-

30 -Ma

--37

Mo

I

I

I

""I

-39

-F

.00

08

-

--50 F

-

-

-.36 F

-

Mo

39

Mo

Mo

the table. CHILE D--30

Site

Dominant vegetation

California

ChileCape

desert scrub coastal scrub scrub sclerophyll scrub sclerophyll (chaparral) montane forest

desert scrub coastal scrub

desert scrub coastal scrub

scrub sclerophyll (mattoral) montane forest

sclerophyll (fynbos) sclerophyll (fynbos)

type

scrub scrub

desert scrub: Succulent Karroo (Acocks 1953); maritimal site: Uest Coast Strandveld on coastal sands (Taylor 1978); foothill site: 1.5m tall broad-sclerophyllous open-scrub (Kruger 1979); montane site: lou heathland and graminoid-heathland sclerophyllous (Kruger 1979).

-Ma-47

.00 00

02 .00

I CAPE D -.17

-

I Ma-40

-

I

-F

I

of the woody for adjacent similarity Fig. 3. Generic vegetation and analagous sites. D = desert; Ma = maritimal; F = foothill = are similarity Mo = montane. The numbers values 1, (max = min = 0) where similarity 2C/(A + B) wehere A is the number of genera at Site A, B is the number at Site B, and C is the number in common.

192


CALIF

CHILE

CAPE PPt r(mm)

T?c

OCOTILLO

i

i

i

i

i

i?i

i

TORREYPINES 6m

EL TOFO

DESERT

45m

TANQUA

15m

155m

i

MARITIMAL

i

DESCANSO 1050m

i

SITRUSDAL

FOOTHILL

800m

100 80 60 40 20 ?i a m

j

j as

MT LAGUNA 1760m

fma

jasondj

MONTANE

CERRO ROBLES

i

i?i?i?i?i?r?r fmamj

jasondj

WITTEBERG

1800m

air temperature and mean monthly (mean monthly rainfall) Fig. 2. Climate diagrams and the Cape. The shaded area represents the warm, dry period. Cape data from Chile, Technical Dotted lines in the Cape climatic indicate Services. Agricultural diagrams climatic stations (see text). nearby

1670m

for desert-to-montane transects in California, S. A. Weather Bureau and the Department of that climatic data had to be adapted from

193


trate

low floristic

sizes

Leaf

and

between

similarity

growth

the California

and Chile sites (Cody & Mooney 1978, and the Cape desert and maritimal sites Specht 1979), (Taylor 1978, Kruger 1979, Goldblatt 1978). Small leaf

sites.

analogous

forms

a characteristic

size,

of

Parsons & Moldenke (1975) found corresponding leaf sizes for analogous sites in California and Chile. They found a parallel increase in leaf size along the aridity

with nutrient-poor

gradient from the desert sites to themontane sites (Fig. 4). Leaf size was discussed by them in terms of the heat stress

addition

: under

argument leaves

are able

of

severe

lower

leaf

conditions to maintain

heat

stress

smaller (Gates

temperatures

1968). In the Cape a similar trend of increasing leaf size occurs from the desert to the maritimal site but both the Cape foothill and montane sites are characterised by a high proportion of small-leafed (leptohyll) individuals (Fig. 4). This high proportion is not consistent with the heat stress deficiencies and

it in terms

interpret

of

nutritional

in the soil. The vegetation of the Cape foothill

montane

restricted

we

Rather

argument.

sites

as

is known

to nutrient-poor

soils

fynbos. derived

It from

is generally sandstones

and quartzite of the Cape Group (Taylor 1978, Kruger 1979). The soils are much poorer in nutrients than those of

demonstrated

to be

appears

fynbos,

associated

soils (Small 1973). Beadle (1966) has

that

the

of

degree

of phosphorus

and

can

xeromorphy

reduced inmany typical Australian

be

sclerophyll taxa by the

nitrates.

Growth

forms in California and Chile show little to those of analogous sites at theCape (Fig. 5). In similarity California and Chile there is a parallel progression from a incidence

high

of

at

drought-deciduousness

the

desert

sites to a low incidence at the foothill sites; the montane is characterised

site

a high

by

incidence

of winter-decidu

ous

individuals. The drought-deciduous habit is almost totally lacking at the Cape sites, where it is represented only at the maritimal site by a small percentage of indivi duals. Unlike themontane sites of Chile and California, the at

vegetation

the Cape

no

evergreen;

is almost

site

was

deciduousness

is sometimes

habit

evergreen

montane

winter

associated

exclusively

recorded.

with

The

nutrient-poor

conditions where the cost of rebuilding deciduous photo organs

synthetic

may

too

place

great

a burden

on

the

plant's nutritional resources (Monk 1966, Small 1973). The most striking differences in growth forms are between the Cape

montane

and Chile.

site and

Broad-leaved

the analogous

in California

sites

winter-deciduous

occur

forests

in

California and Chile whereas the vegetation at the Cape montane site is a low, leptophyll, evergreen scrub (Table 1). We

believe

that

this

is probably

divergence

due

to

soil

differences. are

Succulents

the most

economical

in terms

plants

of the

ratios of carbon fixed to water lost (Ting & Szarek 1975), and

are

aridity

therefore

well on

gradient

all

at

represented three

continents

the xeric (Fig.

end

the

of

5). However

the Cape site is strongly divergent in having a much higher of

proportion

succulents.

the

deciduousness,

Drought

dominant growth form at the desert sites inCalifornia and Chile, is lacking at the Cape site. The dominance of in

succulence and

grazing

of Fig. 4. Percent leaf-size categories montane

transects

individuals at four

is partly

erosion.

Heavy

due

to

selective

winter

stocking

over has

eliminated edible shrubs (Acocks 1953) many of which are drought deciduous (pers. obs.). Subsequently the vegetation becomes dominated by succulents (Acocks 1953, Joubert 1968, Olivier 1966). Nevertheless even in an

:Chile :Calif ' Cape

225 mm 1125mm 2025 mm

the Cape soil

undisturbed

of woody

analogous in California, Chile

taxa with

each

of five

on the desert-to points and the Cape.

Cape

Only growth

state,

semi-desert

succulents vegetation

dominate

in this

(cf. Acocks

1953).

and

other

the foothill sites on all continents have similar forms;

all are dominated

194


by evergreen

individuals.

fc? CAD r?H CAD CAL CH >CAL CH1 CAP ' CAPE ' CAP MAR FOO MON DES MON MON FOOTHILL DESERT MARITIMAL

Viso

U

U

70

50 ? z~ 430

?

8 200-^ CH= CHILE CAL- CALIFORNIA CAP- CAPE SITE DES- DESERT - MARITIMAL SITE MAR SITE FOO- FOOTHILL SITE MON-MONTANE 6. Classification

Fig.

80+ \

\

I

4 \ \

\

D CHILE

CALIF A CAPE

of

growth-forms

evergreen growth-form is another, leaf-size leptophyll

(e.g. %

4)

taxonomic

character, % was the constructed dendrogram using function and average (Orl?ci linkage clustering

are montane

sites assesed

between

Similarities

distribution

The

both

40?\

etc.). value

absolute 1975).

a preponderance

with

forests

(Fig. 5) is one

of winter

deciduous individuals, features which are shared with no other site. The dendrogram indicates that the Cape sites

4 \ SUCCULENT

20+

of sites.

the percentage using and leaf sizes (Fig.

D^^>^

show

little

to analogous

convergence

on

sites

con

other

tinents. The Cape desert site shows very little similarity to other

any

+90

--^^/A

EVERGREEN /

/^^\\ I

/ /

montane

i50i

\

+30 o"?

\ ///

montane

foothill

XERIC-^MESIC Fig.

5. Percent

of

individuals

and succulent evergreen sites on the desert-to-montane

taxa with deciduous, of woody at four analogous climatic transects Chile and in California,

habits

the Cape. as

shown

the Cape

above,

a much

has

higher

incidence of small-leafed individuals. The dendrogram (Fig. 6) summarizes the growth-form and

leaf size

evident

that

similarities

sites in California other California

than

among

the vegetations

to

other

and Chile

of

sites

on all continents.

the climatically

and Chile are more sites montane

on

the sites,

same

It is

analogous

show

sites,

the sites

most

resembles

the greatest

similarity.

incidence

of

is similar

spinescence to analogous

at the desert sites

and mariti

at California

and

Chile; at the Cape foothill and montane sites spines are almost totally lacking. The distinction between the two types of spines (leaf and branch) shows no significant trends (cf. Parsons & Moldenke 1975). If it is assumed pressures

However,

site

A general trend observed for California and Chile is that spines are important in the desert and foothill sites, but less so in themaritimal and montane sites (Table 2). In the Cape

maritimal

maritimal

Spinescence

mal desert

the Cape

site;

closely the Chile and California foothill sites, and the two sites having nutrient-poor soils, the Cape foothill and

fynbos

by

that

spines

can

communities

have

animals,

browsing

perhaps

evolved

under

the

absence

be

explained

selective

in the Cape by

the

low

nutritional value of fynbos grazings (Louw 1969), and thus low grazing pressure. Janzen (1974) has suggested that evergreen

plants

of

nutrient-poor

soils

have

low

palat

ability.

similar to each continents.

however,

do not

The

Floristic

richness

form

a group due to differences in leaf size (Fig. 4). Nevertheless,

The total numbers of species, genera and families of the

195


2. Percentage at analogous sites

Table

individuals

spinescent in California,

and

Chile,

of woody vegetation the Cape.

even the Cape foothill and montane though ence more summer rain than the corresponding

sites

experi

Chile

and

California

sites (Fig. 2). The higher summer rainfall is unlikely to account for the divergence of the Cape sites as one would not expect a higher incidence of small-leafed shrubs and a lack of winter-deciduous shrubs under these

'fo Individuals Branch

Leaf

Total

spines

spines

spines

climatic Desert

The

California

68

55

13

Chile

38

3

41

Cape

43

0

43

conditions.

unexplained.

Chile

9 0 1

15

Cape

desert

and maritimal

The

Cape

sites

fynbos

are more

similar

to

each other than to their analogous sites in California and Chile. Soil factors are of overriding importance in deter

90

9 9

the Cape

sites to the analogous sites in California and Chile, especially the very high desert succulence in the Cape, is

Maritimal California

of

non-convergence

mining

16

the

contrasts

among

of low nutrient conditions

these

areas.

The

in determining

importance

fynbos corn

Foothill California

3

Chile

22

25 32

15

Cape

17

0

0

0

Montane Oil

California

1

11

Chile

12

Cape 111

found in each of the study sites are 7. The major differences in richness

woody vegetation presented in Fig. among

sites

analogous

occurs

at the foothill

and montane

sites, where the Cape is far richer than Chile and California in species and genera. The differences are especially pronounced

at

also

in families.

richer

nutrient-poor

the montane

this

show

site

the Cape

and

its Australian

to nutrient-poor

restricted

the The

non-convergence. fynbos

is

that

it appears

again

the Cape

of is also

which

analogue,

sites

fynbos richness

spectacular

sites. At

Once

soils

(Specht 1979), is a matter of much interest (cf. Naveh & Whittaker 1980). At the Cape maritimal and desert site where

soils

are

richer,

the floristic

than the foothill and montane intercontinental

richness

is much

lower

sites, and appears to show

convergence.

Conclusions

This

study

reveals

that

under

similar

climatic

constraints

the structure of genetically distinct plant communities need not

necessarily

converge.

Because

climatic

types

were

specifically chosen to correspond, it is unlikely that climatic factors could explain this lack of convergence

7. Venn diagrams the total number of species, illustrating of the woody of the vegetation genera and families component at each study site, and the numbers of each in common between and among sites. Where there is overlap between analogous sites the total number of taxa at each site is represented in brackets.

Fig.

196


structure

munity

has been

and

now

It would

&

Briggs'

a comparative

to conduct

be of value

and inAustralia

in Johnson

(1978) treatment of the Cape flora. in

the

levels

are

structure

soil nutrient

where

and

heathlands,

(1975) and Goldblatt's vegetation

P. 1978. An analysis of the flora of southern Africa: Goldblatt, Its characteristics, and origins. Ann. Missouri relationships, 65: 369-436. Bot. Gard.

& Whittaker's

(1979) treatment of mediterranean

(1980) and Specht's shrublands

in Naveh

stressed

two

(cf. Milewski

regions

i.e. at the Cape

low,

similarly

of

study

mediterranean

1979).

1974. Tropical D.H. and blackwater rivers, animals, 6: 69-103. fruiting by the Dipterocarpaceae. Biotropica 1975. On the Proteaceae L.A.S. & B.G. Briggs. the Johnson, evolution and classification of a southern Austral. J. family.

Janzen, mast

Bot.

11:21-61.

Joubert,

J.G.V.

Kruger,

central

and

in southern

the Cape,

South

Africa

extent

the

on floristic

richness,

and sites

analogous

convergence. leaf

leaf duration,

form,

the woody

ana

been

collected

plants,

by

(1975) from analogous climatic sites

Parsons & Moldenke in California

have

were

Chile,

in the Cape.

with

compared Considerable

from

data

in

convergence

vegetation structure between floristically distinct but climatically similar sites in California and Chile has been demonstrated by Parsons & Moldenke (1975). Cape

adaptive

principal show

major

sites

on

can

than

rather

other

fynbos

the

these

communities the

is

deciduousness

communities

fynbos

at

communities

analogous

the

divergence

of

the other

continents

nutrient-poor

soils

Much

the vegetation to

attributed has

desert

Cape

from

continents.

and

fynbos

be

strategy.

to

convergence

Cape

drought

differences

the

between

In

regions.

succulence

little

shows

however,

vegetation, mediterranean

of

on

which

evolved.

References J.P.H.

1953. Veld

Acocks, Surv.

S. Afr. No.

Beadle,

N.C.W.

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types 1-128.

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of the Australian to xeromorphy

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Bot.

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F. di & H.A.

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climatic

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