LIFE FORM AND LEAF SIZE
4.1. Introduction
4.1.1. Life form and biological spectrum
The classification of vegetation based on the appearance of the general nature of
the plant viz., size, form, whether it is evergreen or deciduous, herbaceous or
woody and the position of the buds in the dormant season indicate the "growth
form" or "vegetation form" or "Life forms". These life forms are important
criterion in judging the climate of a region (Mber-Homji, 1964). The pattern in
life forms explains the appearance of plant communities and also indicates the
biotic influence in disturbed plant communities. In many plant explorations, it is
not possible to identify all the species immediately, but they can be classified
according to life forms. Thus, a preliminary picture of the ecological character of
the plant communities may be obtained (Braun-Blanquet, 1932).
oY \ 5 o 5 ''
It was Humboldt in 1806 formulated the concept of life form and termed it as
'vegetative form'. He attempted, grouping of the vegetation types on a
physiognomic basis and identified 15 groups of plants. In the year 1872,
Grisebach developed a system based on the idea of Humboldt's and emphasized
the dependence of life forms on climate. Later on, several workers have put forth
their own system of life form classification (Schimper, 1898; Raunkiaer, 1934).
Cain (1950) reviewed the world literature on life forms and phyto-climate and
Life form and heafsit^e
201
^ ^
found that the Raunkiaer system (Raunkiaer, 1934) is the only system that has
received worldwide use and is simple, clear and compact.
4.1.2. Raunkiaer's life form classification
Raunkiaer (1934) developed life form classification based on the degree of
protection to the perennating buds in the unfavorable conditions. The perennating
buds (meristamatic tissue) are the most critical tissue to be affected, which stops
the growth of a plant. Therefore, the amount of protection provided to the
embryonic growing tissue and the success in enduring the unfavourable period
represents critical adaptation. It is for this reason that Raunkiaer selected the
protection of perennating buds as the principal basis of his life form classification.
Raunkiaer defined the life forms theoretically as "the sum of adaptations of plants
to the climate". He first used the life form spectra to assess the phyto-climate of a
region. He called the expression of percentage of life forms of a region as
"Biological Spectrum" or "Phyto-climatic Spectrum". He classified the life forms
into five major classes.
Class I: Phanerophytes (Ph) - They are any tall plants visible all year round,
which can afford to carry their perennial buds well up in the air, at least 25 cm
up. This would include all trees, lianas, and virtually all shrubs in the
structural classification
Class 11: Chamaeophytes (Ch) - They are low growing plants that are visible
all the year-round, which carry their perennial buds anywhere from the ground
to about 25 cm up. They are capable of handling rougher environments than
Life form and L^eafsi^
202
phanerophytes because of their low stature (they are exposed to less wind and
some ground warming)
Class III: Hemicryptophytes (H) - They die back, to buds at ground surface
during the rough season. Their perennial buds lie close to the ground surface
(above or below) and are often hidden by litter in the rough season, which
protects them. So they are "half-hidden" plants
Class IV: Cryptophytes (Cr) - The surviving buds or shoot apices in this
group of plants are buried in the ground (or under water)
Class V: Therophytes (Th) - They get through bad times (seasonal or even
years long) as seeds or spores. They go through their entire life cycle, from
seed/spore to seed/spore, within one growing season, which can be amazingly
short
Plant climate of a region, according to Raunkiaer (1934), is characterized by the
life form(s), which in the biological spectrum of the region exceeds the percentage
of the same life form in the normal spectrum. Normal spectrum is the theoretical
spectrum given by the whole flora of the earth.
Raunkiaer with his life form classification divided the earth in to three main
ph54o-climates.
(1) Phanerophj^ic climate in tropics (biological spectrum dominated by
phanerophytes)
(2) Therophytic climate in desert (therophytes are the dominant life forms)
(3) Hemicrj^tophytic climate in the greater part of the cold and temperate
zone (abundance of hemicryptophytes compared with normal spectrum).
Lifeform and Leafsit^e
203
Some of the studies on biological spectrum in India are given below.
Nanophanero-chamaeophytic climate was observed in Poona region wherein the
dry period existed for seven months, whereas in Andhra region, phanerophytic
climate was noted (Ferreira, 1940). Kaul and Siran (1976) noted the geochamaeophytic climate in mountainous Bhaderwah of Jammu and Kashmir and
observed that phanerophytes and therophytes that decreased from the lower strata
to higher. Sharma (1990) found thero-cryptophytic phyto-climate in the hilly
terrain of Punjab State, and he attributed that to hot and dry climate prevailing in
the area leading to the dominance of therophytes and cryptophytes. Meher-Homji
(1981) compared 38 biological spectra of various regions of hidia and found the
biological spectra are very much related to the prevailing bio-climate of the
region.
Information on biological spectrum of Kudremukh National Park in the Western
Ghats and its relationship with the prevailing climate is lacking. Hence, the
present study was taken up.
4.1.3. Leaf size spectra
Plants in the tropical forests show several characteristic features in the form and
arrangement of their photosynthetic organs. Many such traits as leaf size, shape,
arrangement and form show strong correlation with the prevailing environment
/
V
(Richards, 1952) and, also, they are determined by the climatic conditions of the
area.
Life form and Leafsi^e
204
The leaf size spectrum of an area gives an idea of the interrelationships of plants
and the prevailing environment. It can also be used as a physiognomic character in
assessing the field relationships of vegetation in different geographic regions. The
leaf size and shape are highly sensitive to soil moisture conditions. The size and
shape of the fossil leaves are potential indicators of paleoprecipitation and helps in
the reconstruction of paleoclimate (Peter et al., 1998). The relationship between
environmental factors and leaf size (growth form attribute) helps in studying the
V'"'
vegetation at regional scale (Floret et al., 1990).
Leaf size classification is the brainchild of Raunkiaer (1934). He has chosen
obvious morphological characters like dimension of transpiring surface as an
index of adaptation to prevailing climatic conditions. Based on the dimension of
the leaves, he classified the leaf size into six different classes (Table 19). The
dimensions of the leaf can be calculated as the two thirds of the recorded
rectangular area formed with its length and breadth (Cain and Castro, 1959).
It is generally observed that leaves are large in moist tropical vegetation
(equatorial rain forests), medium in temperate and small in drier areas. In the
tropical rain forests at least 80% of the species exhibit mesophyll leaf size class
and, interestingly the emergent trees have high percentage of mesophyll leaves
(Richards, 1952). Generally, leaf size tends to decline towards drier areas with
prolonged dry season (Janzen, 1975).
Leaf size spectra of flora and communities are not widely available, as the way
life form spectra are. Brown (1919) studied the relation of leaf type to altitude in
Life form and Leafst^e
205
Table 19: Leaf area of different Raunkiaer leaf size classes and their characteristic
leafAvidth
Raunkiaer leaf class
2
Characteristic leaf width (cm)
Leptophyll
Leaf area (cm2)
up to 0.25
Nanophyll
0.25 - 2.25
7.5
MicrophyD
2.25 - 20.25
22.5
Mesophyll
20.25 - 182.25
67.5
Macrophyll
182.25 - 1640.25
202.5
Megaphyll
> 1640.25
607.5
2.5
'Raunkiaer (1934)^
Two thirds of the product of length and width of leaves
^avinish(1978b)'^
mountains of the Philippines and found dominance of mesophyll leaf class.
Interestingly, he noted equal representation of both mesophyll and microphyll leaf
size classes in montane rain forests. Richards (1952) studied the leaf size in the
tropical rain forest of Shasha Reserve, Nigeria and showed the predominance of
mesophyll leaf size class. A study conducted by Cain et al. (1955) in the Brazilian
rain forest revealed the predominance of mesophyll leaf size class. Cain et al.
(1956) analyzed the leaf size classes of plants on a 2 ha sample plot of rain forest
at Mucamo, Belem and found smaller leaf size classes are better represented
among taller trees and poor representation of larger leaf size classes among tallest
trees. The study conducted by Beard (1946) on the leaf size classes in seasonal
evergreen forests of Trinidad, showed a higher percentage of mesophyll class in
emergent trees as compared to the lower storey. Studies carried out in lowland
forests in Sarawak showed that leaf size in lower strata are frequently smaller than
Lifeform and Lsafsit^
206
those of top canopy and prevalence of micro or leptophyllous species towards
drier and low wind speed sites (Brunig, 1970).
It has been shown that the average leaf width increased with the logarithm of
annual rainfall in well-drained sites of lowland tropics (Givinish, 1984).
Generally, the average width of leaves, their lobes or leaflets tended to decrease
towards dry, sunny or nutrient-poor habitats (Volkens, 1887; Schimper, 1898;
^
^
^
s^'-'Raunkaier, 1934; Shields, 1950; Webb, 1968; Walter, 1973; Hall and Swaine,
1981). Bonnie (2002) used leaf spectra for the estimation of paleoclimates in the
Miocene Tugen hills, Kenya and found that the leaf size is primarily correlated
with yearly or seasonal rainfall and the predominance of non-entire leaf margins
in deciduous plants. Increase in the leaf size with increase in precipitation was
found in Bolivian forests (Kathryn, 2000).
The present chapter describes the biological and leaf size spectrum of Kudremukh
National Park, Western Ghats wherein an attempt was made to understand the
relationship of biological and leaf size spectra and other leaf morphological
parameters with the prevailing climate.
4.2. Materials and methods
4.2.1. Study site and sampling
The study has been conducted in Kudremukh National Park area. The description
of the study site and sampling procedures are detailed in chapter 2.
Lifeform and"Leafsi^
207
4.2.2. Determination of life form and leaf size
Life form of each species was determined as per Raunkiaer system of
classification (Raunkiaer, 1934). The data were collected by 114 random sample
plots. Since it is not possible to document the life form of entire flora of the region
by quantitative quadrat sampling, information already available in the literature
(Gowda, 2(X)4) was also considered for determining the total life forms of the
whole study ^ea.
Leaf area for all the woody species collected from 114 sample plots was
calculated as two thirds of the product of length and width of each leaf and then
assigned to particular leaf size class (Raunkiaer, 1934). Average leaf width for
sample plots was determmed as outlined by Givinish (1978b) using the
characteristic leaf width of each leaf size classes (Table 19). Leaf morphological
characters were also recorded for each woody species.
The environmental and ecological parameters for each sample plot were collected.
The environmental data composed of rainfall (obtained from the World climate
data of
1 km resolution
http://biogeo.berkelev.edu/worldclim/bioclim.htm),
altitude, aspect (the aspect classes were valued from one to eight with the
following values N-3, NE-1, E-2, SE-4, S-6, SW-7, W-8 and NW-5 depending
upon the onset and withdrawal of the rainfall (Pascal, 1988)), and dry months
(duration of the dry period obtained from the bioclimatic map of the Western
Ghats )3Wr*ascal, 1982). The ecological data consisted of percentage evergreenness
(Chandran, 1993), and disturbance levels (based on disturbance index map. Fig.
Lifeform and Ljafsiv^e
208
27 in chapter 2). Canonical Correspondence Analysis (Terbraak, 1987) 'and
Pearson correlation coefficient (Pearson, 1896) were used to explore the
relationship with the ecological and environmental factors and different leaf
criteria. 'Pcord4' software (McCune and Mefford, 1999) was used for the analysis
of the Canonical correspondence and Pearson correlation coefficient.
In the Canonical Correspondence Analysis ordination biplot, the environmental
and ecological variables represented as vectors radiating from the center and leaf
classes were represented by points. The relative length and the angle between
vectors indicated the degree of correlation between variables and axis and among
variables (Terbraak, 1987).
4.3. Results and discussion
4.3.1. Life form and biological spectrum
In the present study, 457 species were recorded from 114 sample plots by random
sampling method. Other plants species (399), which could not be recorded in the
present sinvestigation, but are recorded from the same area by Gowda (2004) were
used for determining the life form in Kudremukh National Park area. Of the total
856 species, 572 were phanerophytes,
152 were therophytes, 57 were
cryptophytes, 47 were hemicryptophytes and 28 were chamaeophytes. The
biological spectrum was computed and compared with Raunkiaer's normal
spectrum. The phanerophytes were the most dominant life form followed by
therophytes and cryptophytes. The hemicryptophytes and chamaeophytes were
under-represented (Table 20).
Lifeform and Leafsi^e
209
Table 20: Biological spectrum of Kudremukh National Park of the Western Ghats
Species recorded
% of species
Normal spectrum
Phenerophytes
572
66.82
46
Chamaeophytes
28
3.27
9
Hemi cryptopyhtes
47
5.49
26
Cryptophytes
57
6.66
4
Therophytes
152
17.76
13
Total
856
100
100
Life fonii classes
'Raunkiaer(1934)
This spectrum of Kudremukh National Park is different from the spectra seen in
the flora of similar tropical vegetation in Uttara Kannada district, the Western
Ghats of Kamataka (Arora, 1960). The high percentage of phanerophytes (66.82)
of the present study as compared to Raunkiaer's normal spectrum could be
attributed to the heavy rainfall and lesser duration of dry months in the area.
However, Raunkiaer's normal spectrum is based on the species present in the
tropical, subtropical and temperate regions of the world. High percentage of
phenerophytes in Kudremukh National Park could also be attributed to
fragmentation and opening of canopies following human intervention and
introduction of herbaceous species from the other adjoining areas. Batalha and
y
Martins (2004) also observed the dominance of phanerophytes in Brazilian
Lifeform and Leaf si^e
^^^
210
Cerrado site, where rainfall is fairy good. Cromer and Pryor (1942) found
exceptionally high percentage of phanerophytes (96) in rain forests of
Queensland. The subtropical evergreen forests also exhibited the dominance of
phanerophytes (Bharucha and Ferreira, 1941). Raunkiaer (1934) observed the
phanerophytic climate in tropical regions with heavy rainfall and he regarded the
annual rainfall as the most important data for the evaluation of life forms, as the
total distribution of rainfall during the year determined the character of the
vegetation.
Comparatively, higher representation of therophytes in the present study area,
with that of Raunkiaer's normal spectrum, could be attributed to the presence of
vast stretches of hill top grasslands. The grasslands generally represent the
therophytic climate (Pondeya, 1964; Singh, 1967; Singh and Yadav, j_974; Singh
and Ambasht, 1975 and Misra and Misra, 1979). Arora (1966) showed a higher
representation of therophytes in the flora of Uttara Kannada district, Kamataka.
Ansari and Singh (1979) also noted therophytic climate in Madhulia forests of
Gorakpur receiving a fairly good amount of rainfall. His results support the
Beadle's (1951) view that the climate cannot always be taken as indicator of a
vegetation of the region. If the therophytes are in large number in a tropical forest,
the presence of hill top grassland vegetation could be predicted as shown in the
present study. Consequently, the life form spectra could be used as an indicator of
the regional phyto-climatic situation.
f''^
%
Lifeform and Leafsif^e
211
4.3.2. Leaf size spectra
Out of 457 species recorded in the present study from the Kudremukh National
Park region, 280 were woody species. Seventy-five per cent of the woody species
belong to the mesophyll leaf size class. The occurrence of mesophyllous species
in the primary evergreen forest is 83.21% followed by shola forest (82.89%) and
was least in the moist deciduous forest (71.60%). A maximum of 78.83% of
species in the primary evergreen system exhibited alternate type of leaf
arrangement and as far as the other vegetation systems are concerned, they did not
differ much. Species with simple leaves are more dominant with 74.29%
incidence as compared to those with compound leaves (25.71%). The percentage
of species with simple leaves is comparatively high (84.62%) in the secondary
evergreen forest than that with compound leaves in semi-evergreen forests
(17.52%). In all the vegetation types, the species with entire leaves, dominated
(85.36%) than species with serrate leaves (14.64%). The secondary evergreen
forests showed high percentage of entire leaves (97.67). The details of the results
were summarized in table 21. As far as the leaf width is concerned, the average
leaf width decreased with increase in altitude (Fig. 42). Grub et al. (1963) and
Grub (1974; 1977) also observed the similar altitudinal trend with average leaf
width in the humid tropics of Southeast Asia, Malaysia, Africa and South
America. Walter (1973) observed the initial increase in leaf width with altitude in
Coastal Cordillera of Venezuela and he attributed that to the orographic rainfall.
Results of the present study also pointed out that, the percentage of
evergreennesss is an important gradient in distributing the leaf size classes among
Ufeform and l^afsi^v
212
Table 21: Leaf-size classes (%), arrangement of leaves (%), nature of leaes (%)
and leaf margin (%) in diiferent vegetation types of Kudremukh National Park, the^
Western Ghats in Kamataka
' Jk
Vegetation type
Category
Primary Secondary SemiMoist
'Shola'
evergreen evergreen evergreen (deciduous
Total
Leaf-size class
Leptophyll
-
-
0.89
1.23
-
0.71
Nanophyll
-
-
1.33
2.47
-
1.07
Microphyll
11.68
13.46
18.67
18.52
14.47
18.57
Mesophyll
83.21
81.73
74.67
71.60
82.89
75.00
Macrophyll
5.11
4.81
4.44
6.17
2.63
4.64
Arrangement of leaves
Ahenate
78.83
77.88
77.33
67.90
72.37
77.14
Opposite
20.44
2M5
21.33
29.63
25.00
21.43
Whorled
0.73
0.96
1.33
2.47
2.63
1.43
Simple
82.48
84.62
74,22
81.48
84.21
74.29
Compound
17.52
15.38
25.78
17.28
15.79
25.71
Entire
86.86
85.58
85.78
82.72
77.63
85.36
Serrate
13.14
14.42
14.22
17.28
22.37
14.64
Nature of leaves
Leaf margin
the different vegetation types (Fig. 43). The Eigenvalue of the three CCA Axes
were 0.009, 0.008 and 0.004 and the total variance ("inertia") was 0.24. Monte
A
Lifeform and Leaf siv^e
I<
213
60
500
1000
1500
2000
Altitude (m above MSL)
Fig. 42: Trends in average leaf width with respect to tlie altitude in the
Kudremukh National Park,'the, Western Ghats in Kamataka
Carlo test indicated a significant (P o.oi) positive correlation of the environmental
and ecological variables with the Axis 2.
Significant positive correlation was observed with the percentage of evergreeness
and mesophyll leaves (P o.oi), alternate leaves (P o.ooi) or simple leaves (P o.os) and
negative correlation with that of evergreenness and microphyll leaves (P o.oi)>
opposite leaves (P o.ooi) or compound leaves (P 0.05)- Elevation positively
correlated with serrate leaf form (P 0.001) and negatively correlated with the entire
leaves (P o.ooi)- Rainfall negatively correlated with leptophyll leaf class (P = 0.05).
Pearson correlation matrix for environmental and ecological and leaf size classes
is given in the table 22.
Lifeform and Leafst\e
214
Axis2
i y^Evergreeness
RainM
MacrophyU
Axis 1
-4
Whorled
2 Aspect T
- Disturbance
-3
Diymonths
Elevation
MicropltyD
Fig. 43: Canonical Correspondence Analysis ordination biptot of leaf morphofogy and environmental
and ecotogical traits inKudreniukhNatbnal Park,/^WesternGhats(m|Kamataka
/vPearson correlation coefficient is a measure of linear association between two
variables. The value of correlation does not depend on the specific measurement
units (Pearson, 1896). Hargis et al. (1999) used Pearson correlation coefficient to
understand the influence of forests fragmentation and forest structure variables
with Marten captures.
The tropical rain forests are characterized by the dominance of mesophyll leaf size
class. The macrophyll and microphyll leaf classes are sparingly represented and
leptophyll and nanophyll leaf class are quite often absent (Richards, 1952). The
results of the present study revealed that 75% of woody species belonged to
Ufeform and heaf si^^e
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Lifeform and Leafsi^e
216
mesophyll leaf class. Leptophyll and nanophyll leaf classes were absent. The
proportional distribution of different leaf size classes in different vegetation types
might suggest their resource sharing and their extent of adaptability to the
surrounding environment. The predominance of mesophyll leaves in the evergreen
vegetation type could be correlated to their habitat preferences, which is a
combination of wetness and heat characteristic of the rain forest climate
(Richards, 1952).
Although, rainfall is the major determinant for the leaf size classes (Richards,
1952; Sringeswara et ai, 2003), the present result does not show any significant
correlation with leaf classes except for leptophyll leaf class, which is negatively
correlated (P=0.05). This could be attributed to the prevalence of less variation in
the rainfall pattern as well as the vegetation types in the whole (of study.
Interestingly, the percentage of evergreeness significantly correlated with that of
the leaf size classes (Table 22).
The percentage of alternate leaf arrangement is high in all the types of vegetation
in the park. The alternate leaf arrangement helps in trapping more light with the
occupation of minimum space. The possession of alternate or opposite leaves is
often a familial character (Cronquist, 1981). The percentage of species with
compound leaves is more in the semi-evergreen and moist deciduous types in the
park, which consisted of more number of pioneer and colonizer species. In case of
compound leaves the transpiration and respiration is reduced following the
shedding the leaf rachis as well as leaflets (Givinish, 1978a; 1978b; 1979). In
addition to this, plants with compound leaves are fast growing and compete for
Ufeform and heafsis^
217
^__
light in forest gaps (Givinish 1978a). In contrast, leptophyll leaves are the
common adaptations to water stress regions. In the present study, species having
leptophyllous conditions are deciduous species (Phyllanthus emblica and Acacia
pennata) and are found in dry habitats (i.e. moist deciduous and semi-evergreen
forests). Brunig (1970) also found the dominance of leptophylls in the stands with
extreme fluctuation of water regime.
The present study revealed that "the percentage of species with serrate leaf
condition increase with increase in elevation. Juliol(2003) also made a similar
observation. The present study reveals that, the average leaf width decreased with
increase in elevation. The decreased leaf width with increase in altitude could be
attributed to the harshness of the prevailing climatic conditions, decrease in soil
fertility and also the influence of high intensity short-wave radiation, which
reduces the leaf growth. Givinish (1984) also observed the decrease of the average
leaf width with increase in elevation. However, Brown (1919) observed the
increase of leaf size with increase in altitude and Bout and Okitsu (1999) also
noted distinct leaf size zonation along an altitudinal gradient in Mt. Pulog, in the
Philippins instead of a continuous change. Dolph and Dilcher (1980a, 1980b)
claimed that the elevational trend in leaf size is discontinuous, and recognized
four foliar belts in which there is little or no systematic variation in leaf size. But
Givinish (1984) disproved the Dolph and Dilcher's claim and noted a continuous
change in the elevation trend with Dolph and Dilcher's data and reasoned the
deviation trend for the application of methodology.