Journal of
Threatened Taxa | www.threatenedtaxa.org | 26 May 2018 | 10(6):
11743–11752
Forest evergreenness and tree endemism in the central Western Ghats,
southern India
Divakar K. Mesta 1 & Ganesh R. Hegde
2
1,2 Postgraduate Department of Studies in
Botany, Karnatak University, Pavate
Nagar, Dharwad, Karnataka 580003, India
1 Present address: Department of Botany,
Carmel College of Arts, Science and Commerce for Women, Nuvem,
Salcete, Goa 403001, India
1 divakarmesta@gmail.com (corresponding author), 2 grhbhadran@rediffmail.com
Abstract: Forests of the Western---- Ghats are
well known for their evergreenness and high
endemism. The present study carried
out in the Sharavathi River Basin in the central
Western Ghats of India is to find the relationship between forest evergreenness and tree endemism. The study was carried out from 2000 to
2006 and the methodology followed is a combination of
transect and quadrat method nested with smaller quadrats for shrub layer
and herb layer. A total of 51
endemic tree species belonging to 20 families were recorded. The results reveal that the composition
of endemic tree population is closely associated with the evergreenness
of the forest. With the increase in
evergreenness, endemism also increased and almost all
the endemic trees of the region occurred in very high evergreen class. Many of them were exclusively found in
very high evergreen forests and ground layer data support this
observation. Such narrow distribution
of endemics makes them most vulnerable to extinction. The present study will be helpful in
understanding the association of endemic trees with evergreenness
of forest and will be useful in conservation as well as restoration of these
endemic trees in their natural habitats.
Keywords: Climax forests, evergreenness,
paleoendemics, transect,
tree endemism, Western Ghats.
doi: http://doi.org/10.11609/jott.3173.10.6.11743-11752
Editor: S.R. Yadav, Shivaji University, Kolhapur, India. Date
of publication: 26 May 2018 (online & print)
Manuscript details: Ms
# 3173 | Received 28 November 2016 | Final received 12 February 2018 | Finally
accepted 25 March 2018
Citation: Mesta, D.K. & G.R. Hegde (2018). Forest evergreenness
and tree endemism in the central Western Ghats, southern India. Journal
of Threatened Taxa 10(6): 11743–11752; http://doi.org/10.11609/jott.3173.10.6.11743-11752
Copyright: © Mesta & Hegde 2018. Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use of this article in any medium,
reproduction and distribution by providing adequate credit to the authors and
the source of publication.
Funding: Logistic
support from Dr. T.V. Ramachandra,
Centre for Ecological
Sciences, Indian Institute of Science,
Bangalore.
Competing interests: The authors declare no competing interests.
Author Details:
Dr. Divakar K. Mesta
holds a PhD from Karnatak University, Dharwad and has several years of forest field experience in
the central Western Ghats. His major field of interests are
field taxonomy, evergreen forest ecology, endemic plants and Myristica swamps and presently works as a Assistant
Professor in Botany. Dr. Ganesh R. Hegde,
Professor of Botany Kranatak University, Dharwad is actively engaged with ecology and plant
diversity studies. He has guided research works pertaining to taxonomy of angiosperms
of Dharwad District, Kumta Taluka of Uttara Kannada District
and Hillocks of neighbouring Dharwad
District. He has several new records of angiosperm plants from Karnataka to his
credit.
Author
Contribution: DKM is
involved in planning field work, data collection,
compilation, analysis of different parameters and preparation of the
manuscript. GRH is actively involved in data analysis, preparation of
manuscript, discussion and interpretation of results.
Acknowledgements: The authors are thankful to Karnatak
University Dharwad for the facility. DKM expresses
his gratitude to Dr. T. V. Ramachandra
for all the support and facility during the present investigation and to the
Principal Sister Aradhana A.C., Carmel College for her
encouragement. We thank the editor and anonymous reviewers for their valuable
comments and suggestions in improving the manuscript.
INTRODUCTION
The
Western Ghats, being one of the 35 global biodiversity hotspots (Marchese 2015), is very rich in plant diversity and
endemism (Nayar et al 2014). Most of the arboreal taxa (63%) of the
Western Ghats are endemic to the region and the evergreen forests are
characterised by a very high percentage of endemic species (Ramesh 2001). The evergreen forests in southern
peninsular India are mainly restricted to the Western Ghats and the tree
endemism in the region shows latitudinal variation with highest endemism in the
southern Western Ghats and gradually decreasing through the central Western
Ghats to the norhern Western Ghats (Pascal
1988). The evergreen forests of the
central Western Ghats act as a transition zone forming the northern limit for
many evergreen and endemic trees (Mesta 2008). Endemics are of high conservation value,
as they are very much restricted in distribution and could be lost forever due
to human-induced threats (Nayar 1996; Miara et al. 2018).
Like other parts of the tropics, the Western Ghats are also one of the
highly human impacted mountainous tracts of the world and various anthropogenic
activities have led to the grim biodiversity scenario; pushing many plant
species to one or the other category of threat. Most of the red listed tree species of
India (53 out of 96) are endemic to the Western Ghats (Nayar
& Sastry 1987, 1988, 1990), indicating the heavy
threat to them. The present study
carried out in the Sharavathi River Basin (SRB) in
the central Western Ghats of India aims at finding the relationship of forest evergreenness and tree endemism in the region.
MATERIAL AND
METHODS
Study Area
The
study was carried out in the SRB, one of the major west flowing rivers of the
central Western Ghats of Karnataka State, India (13.7–14.430N
& 74.4–75.330E) (Fig. 1). The forests range from climax evergreen to evergreen, semi-evergreen and moist deciduous
through which several major streams and substreams
flow out forming the major source of water.
Topographically
the river basin includes three belts, a coastal tract with broad winding
lagoons, rich plains, and wooded hills running to the sea; a central belt of
the lofty Sahyadris covered with magnificent forests;
and the eastern upland, which is undulating and thickly wooded in the west and
in the east passes into a bare level and thickly peopled plain. The elevations vary from sea level to about
1,343m at Kodachadri Hill (Mesta 2008).
The rock formation is Archaean
complex, the oldest rock of the earth crust (Krishnan 1974). A narrow strip of low land in the
western side is covered by alluvium.
Lateritic exposure of the tertiary type as well as more recent is common
in the river basin especially in the coastal lowland. The soils are basically derivatives of
the Dharwar system and the main soil types of the
river basin are coastal alluvium and lateritic (Saldhana
1984; Ramaswamy et al. 2001).
The
average rainfall received is around 3,500–4,000 mm, extending from June
to September. The relative humidity
in the coast is 95% where as in the plains it is about 75%. The mean annual temperature ranges
between 160C and 230C according to altitude (Pascal
1982). The average minimum and
maximum temperature is about 15–38 0C.
The
major vegetation type in the basin includes evergreen and semi-evergreen climax
forests of Persea macrantha–Diospyros spp.–Holigarna
spp. type and Diospyros spp.–Dysoxylum malabaricum–Persea macrantha ÒKanÓ type (Pascal 1988). Part of region belongs to Poeciloneuron facie of Dipterocarpus
indicus–Diospyros
candolleana–Diospyros
oocarpa type in Kodachadri
and Karani.
In addition, there are other secondary formations like moist deciduous, savanna to woodland savanna, shola
type and various monoculture plantations.
The evergreen forests correspond to the Òwest coast tropical evergreen
forestsÓ (Group1/A-C/4) of Champion & Seth (1968).
Sampling
Methods
The
tree sampling method followed for the present study is a
combination of transect and quadrat method nested with smaller quadrats
for shrub layer and herb layer (Chandran & Mesta
2001; Mesta 2008). The transect
length ranged from 140–180 m and quadrats of 20x20 m area were laid
alternatively left and right along the transect leaving an inter-quadrat
distance of 20m throughout the transect. In each tree quadrats, two shrub
quadrates of 5x5 m were laid to enumerate tree saplings and four herb quadrats
of 1x1 m to enumerate tree seedlings.
The number of quadrats laid for each transect was five and in a very few
cases it was four, where the forest patch is smaller. Care was taken to distribute the
vegetation samples throughout the study area. In each tree quadrat of 20x20 m, all the
trees (having a minimum gbh of 30cm) were enumerated
thereby getting the actual number of trees in each quadrat. Myristica
swamps, the relics of primeval forests well known for high endemism, have been
excluded from the present study as a detailed study including endemism was
reported earlier (Chandran & Mesta 2001).
Data
Analysis
All the
sampled transects were classified into five groups based on the percentage of
evergreen individuals occurring, as very high (81–100 %), high
(61–80 %), moderate (41–60 %), low (21–40 %), and very low
(0–20 %) evergreen classes.
The endemic as well as nonendemic evergreens
have been considered for the calculation of percentage evergreenness. The percentage endemic tree population
has been calculated for each evergreen class by pooling all the transect data of
respective evergreen class. The
endemic trees are listed based on the atlas of endemics (Ramesh et al. 1997)
and other regional floras (Cooke 1967; Saldanha 1984,
1996; Dasappa & Swaminath
2000; Mohanan & Sivadasan
2002). The
importance value index (IVI), which gives an overall picture of the importance
of the species in the community by considering the relative values of density,
frequency and basal area in a given sample is calculated by following Elzinga et al. (2001).
RESULTS
A total
of 670 tree quadrats of 400m² each were laid along 130 transects
accounting for a total sampled area of 26.8ha. In all 203 tree species under 55
families were recorded of which 51 species belonging to 20 families are endemic
to the Western Ghats. Of the total
12,404 recorded tree stems, 82% (10,149) of individuals were evergreens while
40% (4,913) were endemic to the Western Ghats. The average value of evergreenness
varied from 7% to 91% and the average endemism from 5% to 36% for very low
evergreen class to very high evergreen class, respectively (Fig. 2).
Composition
of endemics in different evergreen classes
Very
high evergreen class (81–100 % evergreen): Of the 51 endemics recorded,
50 occurred in the very high evergreen class accounting for more than 98% of
recorded endemic tree species of the river basin and 18 of them were
exclusively found in this class.
The dominant endemics found in this evergreen class were Knema attenuata, Hopea ponga, Reinwardtiodendron anamallayanam,
Holigarna grahamii, Diospyros candolleana,
Holigarna arnottiana,
Ixora brachiata,
and Flacourtia montana.
The indicator species of climax evergreen forests of Western Ghats like Palaquium ellipticum,
Vateria indica,
Dipterocarpus indicus
(Image 1), Poeciloneuron indicum, and Dysoxylum
malabaricum were found only in this very high
evergreen class.
High
evergreen class (61–80 % evergreen): The number of endemics drastically
decreased from very high to high evergreen class. Of the 51 endemics, 32 (63%) were
recorded in this class. Major
endemics recorded were Holigarna grahamii, Holigarna
beddomei, and Polyalthia
fragrans.
Other dominant endemics recorded were Garcinia
indica, Blachia
denudata, Dimorphocalyx
lawianus, Sageraea laurifolia, Gordonia obtusa, Hydnocarpus laurifolia, Drypetes elata, and Diospyros saldanhae.
Moderate
evergreen class (41–60 % evergreen): Totally 17 endemics were recorded
here, which is almost 70% less than in the very high evergreen class. Several endemics were absent in this
class and the most dominant species recorded in this class were Holigarna arnottiana,
Ixora brachiate, and Cinnamomum macrocarpum.
Even though Reinwardtiodendron anamallayanam, Diospyros
candolleana, Beilschmiedia
dalzellii and Artocarpus
hirsutus occurred in this class, they were less
in number compared to their relatively abundant nature in the very high
evergreen class.
Low
evergreen class (21–40 % evergreen): As the percentage composition of
evergreens decreased, the endemics also decreased gradually. Only 8 (16%) endemics were recorded in
this class. Tabernaemontana
heyneana is the only dominant endemic and Hopea ponga and Flacourtia montana were
found in a few numbers; however other species like Garcinia
gummi-gutta, Ixora
brachiata, Vepris
bilocularis, Knema
attenuate, and Holigarna arnottiana were represented by one or two individuals
only.
Very
low evergreen class (0–20 % evergreen): Only four endemics Tabernaemontana heyneana,
Flacourtia montana,
Calophyllum apetalum,
and Garcinia gummi-gutta
were recorded here. The latter two were represented by single individuals only.
Endemic trees in the ground layer
The
shrub and herb quadrat data representing tree saplings and seedlings followed
the similar trend as in the tree quadrats. The number of endemic tree species
in shrub layer across different evergreen classes were 40, 25, 10, 3, & 4
and in herb layer 42, 23, 9, 5 and 6.
Importance value index (IVI)
The IVI
shared by endemics varied from species to species across different evergreen
classes. In case of very high
evergreen class all the endemic trees together shared the IVI of 112 followed
by 76, 51, 38 and 12 for high, moderate, low and very low evergreen class
respectively. Major endemics
contributing to the IVI in the very high evergreen class were Knema attenuata, Reinwardtiodendron anamallayanam,
Hopea ponga, Holigarna grahamii,
Diospyros candolleana,
and Holigarna arnottiana;
in the high evergreen class by Ixora brachiata, and Flacourtia
montana; in the moderate by Holigarna
arnottiana, Ixora
brachiata, and Cinnamomum
macrocarpum and in very low and low evergreen
class by the deciduous endemic Tabernaemontana
heyneana.
Table 1. List of endemics with their
composition in different evergreen classes (figure in parenthesis is IVI value)
|
Plant species |
Family |
Evergreen classes |
||||
81–100 |
61–80 |
41–60 |
21–40 |
0–20 |
|||
1 |
Actinodaphne angustifolia Nees1 |
Lauraceae |
1.16 (3.03) |
1.49 (3.46) |
1.52 (3.34) |
|
|
2 |
Aglaia lawii (Wight) Sald.1 |
Meliaceae |
0.18 (0.04) |
|
|
|
|
3 |
Arenga wightii Griff.3 |
Ar |
0.10 (0.13) |
|
|
|
|
4 |
Artocarpus hirsutus Lam.1 |
Moraceae |
1.23 (2.95) |
0.74 (3.79) |
0.38 (1.41) |
|
|
5 |
Beilschmiedia dalzellii (Meis.) Kost.2 |
Lauraceae |
1.17 (3.47) |
0.81 (2.15) |
0.38 (1.25) |
|
|
6 |
Blachia denudata Benth.1 |
Euphorbiaceae |
|
0.07 (0.16) |
|
|
|
7 |
Calophyllum apetalumWilld. 1 |
Clusiaceae |
0.07 (0.25) |
0.07 (0.38) |
0.19 (0.51) |
|
0.14 (0.36) |
8 |
Cinamomum macrocarpum Hk. f.1 |
Lauraceae |
1.05 (2.52) |
2.23 (4.98) |
3.42 (7.84) |
|
|
9 |
Dimorphocalyx lawianus (Muell.-Arg.) Hk.f.1 |
Euphorbiaceae |
0.20 (0.64) |
0.27 (0.55) |
|
|
|
10 |
Diospyros angustifolia (Miq.)
Kostermans1 |
Ebenaceae |
0.08 (0.11) |
|
|
|
|
11 |
Diospyros candolleana Wt.1 |
Ebenaceae |
2.49 (5.41) |
2.03 (3.96) |
1.71 (3.87) |
|
|
12 |
Diospyros paniculata Dalz.1 |
Ebenaceae |
0.72 (1.59) |
|
|
|
|
13 |
Diospyros pruriens Dalz.1 |
Ebenaceae |
1.02 (2.28) |
|
|
|
|
14 |
Diospyros saldanhae Kostermans1 |
Ebenaceae |
0.06 (0.26) |
0.07 (0.12) |
|
|
|
15 |
Dipterocarpus indicus Bedd.1 (Fig. 5) |
Dipterocarpaceae |
1.39 (2.99) |
|
|
|
|
16 |
Drypetes elata (Bedd.) Pax & Hoffm.1 |
Euphorbiaceae |
0.59 (1.25) |
0.07 (0.17) |
|
|
|
17 |
Drypetus confertiflorus
(J. Hk.) Pax & Hoffm.1 |
Euphorbiaceae |
0.02 (0.28) |
|
|
|
|
18 |
Dysoxylum malabaricum Bedd.1 |
Meliaceae |
0.11 (0.34) |
|
|
|
|
19 |
Eugenia macrosepala
Duthie1 |
Myrtaceae |
0.48 (1) |
|
|
|
|
20 |
Euonymus indicus Heyne ex Wall.1 |
Celastraceae |
0.59 (0.77) |
0.07 (0.11) |
0.38 (1.05) |
|
|
21 |
Flacourtia montana Grah.1 |
Flacourtiaceae |
1.40 (3.17) |
3.45 (7.33) |
1.52 (2.88) |
1.08 (5.86) |
0.57 (1.51) |
22 |
Garcinia gummi-gutta (L.) Robson1 |
Clusiaceae |
1.13 (2.86) |
0.61 (0.97) |
0.15 (1.15) |
0.72 (1.79) |
0.14 (0.37) |
23 |
Garcinia indica (Thouras)
Chois.1 |
Clusiaceae |
0.01 (0.04) |
0.20 (0.35) |
|
|
|
24 |
Garcinia talbotii
Raiz. ex Sant.1 |
Clusiaceae |
0.28 (0.93) |
|
|
|
|
25 |
Gordonia obtusa Wall ex Wt. & Arn.1 |
Theaceae |
0.24 (0.36) |
0.14 (0.32) |
|
|
|
26 |
Holigarna arnottiana Hk. f.1 |
Anacardiaceae |
2.46 (5.32) |
4.13 (8.95) |
5.31 (12.8) |
0.36 (4.52) |
|
27 |
Holigarna beddomei Hk. f.1 |
Anacardiaceae |
0.42 (1.46) |
0.20 (0.54) |
|
|
|
28 |
Holigarna ferruginea March.1 |
Anacardiaceae |
0.54 (1.49) |
|
0.19 (0.53) |
|
|
29 |
Holigarna grahamii (Wt.) Kurz. 1 |
Anacardiaceae |
3.10 (7.62) |
2.03 (5.07) |
|
|
|
30 |
Hopea parviflora Bedd.1 |
Dipterocarpaceae |
0.11 (0.62) |
|
|
|
|
31 |
Hopea ponga (Dennst.)
Mabberly1 |
Dipterocarpaceae |
7.42 (11.4) |
1.49 (4.16) |
0.19 (0.53) |
2.16 (3.79) |
|
32 |
Hydnocarpus laurifolia (Dennst.)
Sleumer1 |
Flacourtiaceae |
0.31 (1.34) |
0.07 (0.29) |
|
|
|
33 |
Ixora brachiata Roxb.1 |
Rubiaceae |
1.67 (2.95) |
4.13 (8.27) |
3.80 (8.29) |
0.72 (3.17) |
|
34 |
Knema attenuata (J. Hk. & Thw.) Warb.1 |
Myristicaceae |
10.01 (16.4) |
4.06 (8.93) |
0.38 (1.05) |
0.36 (2.42) |
|
35 |
Litsea laevigata (Nees) Gamble1 |
Lauraceae |
0.06 (0.27) |
0.41 (0.9) |
0.38 (0.51) |
|
|
36 |
Mammaea suriga (Buch.-Ham. ex Roxb.)
Koest.1 |
Clusiaceae |
0.04 (0.07) |
|
|
|
|
37 |
Mastixia arborea (Wt.) Bedd.1 |
Cornaceae |
0.44 (1.47) |
0.07 (0.2) |
|
|
|
38 |
Meiogyne pannosa (Dalz.)
Sinclair1 |
Annonaceae |
0.13 (0.26) |
|
|
|
|
39 |
Myristica fatua var. magnifica (Bedd.) Sinclair1 |
Myristicaceae |
0.01 (0.05) |
|
|
|
|
40 |
Myristica malabarica Lam.1 |
Myristicaceae |
0.92 (2.16) |
0.14 (0.25) |
|
|
|
41 |
Palaquium ellipticum
(Dalz.) Baill.1 |
Sapotaceae |
0.54 (0.73) |
0.07 (0.32) |
|
|
|
42 |
Poeciloneuron indicum L.1 |
Clusiaceae |
1.30 (2.44) |
|
|
|
|
43 |
Polyalthia fragrans (Dalz.) Bedd.1 |
Annonaceae |
0.68 (1.99) |
0.41 (1.27) |
|
|
|
44 |
Reinwardtiodendron anamallayanam
(Bedd.) Sald.1 |
Meliaceae |
7.06 (12.26) |
2.37 (4.02) |
0.95 (1.98) |
|
|
45 |
Sageraea laurifolia (Grah.) Blatt.1 |
Annonaceae |
0.18 (0.61) |
0.14 (0.34) |
|
|
|
46 |
Syzygium laetum (Buch.-Ham.) Gandhi1 |
Myrtaceae |
0.08 (0.59) |
|
|
|
|
47 |
Syzygium travancoricum
Gamble1 |
Myrtaceae |
0.03 (0.07) |
|
|
|
|
48 |
Tabernaemontana heyneana Wall.5 |
Apocynaceae |
0.34 (0.89) |
1.62 (2.88) |
0.76 (2.04) |
8.99 (15.91) |
3.98 (9.87) |
49 |
Tricalysia apiocarpa Gamble1 |
Rubiaceae |
0.01 (0.04) |
|
|
|
|
50 |
Vateria indica L.1 |
Dipterocarpaceae |
0.44 (1.13) |
0.07 (0.16) |
|
|
|
51 |
Vepris bilocularis (Wt. & Arn.)
Engler1 |
Rutaceae |
0.51 (1.4) |
0.27 (0.53) |
|
0.36 (1.03) |
|
|
Additional endemics recorded outside the
sampling area |
|
|
|
|
|
|
52 |
Gymnacranthera canarica (King) Warb.
1 |
Myristicaceae |
|
|
|
|
|
53 |
Madhuca bourdillonii (Gamble) H.J. Lam.1 |
Sapotaceae |
|
|
|
|
|
54 |
Pittosporum dasycaulon L. 2 |
Pittosporaceae |
|
|
|
|
|
55 |
Pterospermum reticulatum L. 2 |
Sterculiaceae |
|
|
|
|
|
56 |
Semecarpus kathalekanensis
Das. &
Swam.4 |
Anacardiaceae |
|
|
|
|
|
Note: 1 Ramesh et al. 1997; 2 Saldanha, 1984–1996; 3 Mohanan
& Sivadasaan 2002; 4 Dasappa & Swaminath 2000; 5
Cooke 1901–1908.
DISCUSSION
The
average endemism across the five evergreen classes in SRB ranged from 5% to 36%
and most of the endemics were distributed in a very high evergreen class. According to Ghate
et al. (1998) the average endemism for the evergreen forests of the Western Ghats
is around 41% and for the closed canopy evergreen forest 55%. Elouard et al.
(1997) studying the evergreen forest patch at Kodagu,
one of the dense forest areas of the Western Ghats in Karnataka, found 48% of
tree endemism. Sreekantha
et al. (2007) recorded 71% of tree endemism for a forest patch in the SRB. The present study shows that endemism in
SRB (except for four transects which had zero endemism) ranged from the lowest
of 3% at Chikandagudda to 84% at Tulsani
which is exceptionally high compared to any of the evergreen forests of the
Western Ghats. Further, several
localities in the very high evergreen class have more than 50% endemism.
Apart
from the 51 endemics recorded under tree quadrats, an additional five endemics
were recorded during the opportunistic visits. They are Gymnacranthera
canarica, Madhuca bourdillonii, Pittosporum dasycaulon, Pterospermum
reticulatum, and Semecarpus
kathalekanensis. During the present study, seven
individuals of Madhuca bourdillonii had been recorded close to a steep curve
along the roadside of Malemane Ghat.
Myristica swamps, the relics of primeval
forests well known for high endemism, have been excluded from the present study
as a detailed study including endemism has been reported (Chandran
& Mesta 2001). These swamps in
the southern Western Ghats are also known for high endemism (Varghese & Menon 1999). Gymnacranthera canarica
and Semecarpus kathalekanensis
are associated with these swamps in the river basin. Even though Pterospermum
reticulatum is a rare (Nayar
& Sastry 1990) and Vulnerable (World Conservation
Monitoring Centre 1998) endemic, it is quite frequently seen in the Gersoppa and Malemane Ghats,
usually along the forest edges.
The
high degree of endemism in the evergreen forests of the Western Ghats can be
attributed to the isolation of the ghats from other
moist formations and the prevailing drier climatic conditions in the
surrounding areas. For the whole of the Western Ghats, the variation in the
degree of endemism is determined by two factors: the increasing number of dry
months from south to north and decrease in temperature with increase in
altitude (Pascal 1988). But for the
SRB there seems to be multiple factors responsible for variation in evergreenness and endemism. In addition to the rainfall and the dry
period of 5–6 months, the local topography seems to play an important
role. The drainage pattern of the riverbasin indicates higher drainage density towards the ghat region with rugged hills and deep valleys, while the
eastern flatter terrain has lower drainage density. Analysis of rainfall data indicates that
(Fig. 3) the rainfall increase from west coast to east up to the ghat reagion, then decrease
towards the plains in the east near Sagar and Rippenpet region.
Similarly, from north to south it has an increasing trend with maximum
rainfall at Kogar. Karthick &
Ramachandra (2006) reported that the rainfall is
highest in the ghat region and least in the plateau
of SRB.
Western
Ghats, one of the oldest landmasses of the Earth is related to Gondwana land in origin. Many of the endemic trees of the Western
Ghats like Poeciloneuron indicum, Myristica fatua var. magnifica,
and Gymnacranthera canarica
are very old in origin and are called palaeoendemics. They bear testimony to the days
when continents like America, Africa and Asia constituted a single landmass
called Gondwana.
In SRB, such relics of primary forests can be seen in Kathalekan where M. fatua
var. magnifica, G. canarica,
and Semecarpus kathalekanensis
were found. Similarly Vateria indica and Poeciloneuron indicum
were found in only two primary evergreen forest patches in the river basin. All
such paleoendemics and some indicator species of
climax evergreen forests like Dipterocarpus
indicus, Palaquium ellipticum, etc. were recorded only in the very high
evergreen class.
The
average annual rainfall in the river basin is 3,500–4,000 mm. The rainfall above 2,500mm in Western
Ghats support evergreen forests (Pascal 1988) and the evergreen forests in the
river basin are restricted to the ghat region whereas
the eastern plateau is dominated by moist deciduous forest, since the latter
receives less than 2,000mm rainfall.
These regions, however, were known to have evergreen ÔKanÕ forests in the past (Brandis
& Grant 1868). The drier
condition and low rainfall, in association with anthropogenic factors like
agriculture, fuel wood collection and cattle grazing through the last many
centuries have altered the vegetation of this eastern plateau region. The forests in the lower rainfall araeas of the Western Ghats are more fragile and are
therefore prone to lose their evergreenness faster
than those in the high rainfall areas mainly due to fire. Most of the delicate, thin barked
evergreens disappear from such region and only thick barked deciduous trees
like Terminalia spp,
Xylia xylocarpa,
Dillenia pentagyna,
Careya arborea (Rao 1891) and the deciduous endemic Tabernaemontana
heyneana can survive the conditions.
The
ground layer data reveals that many of the endemics have saplings and seedlings
under their preferred evergreen classes; however, there are noticeable numbers
of species which do not have saplings or seedlings
which is a serious matter of concern (Table 2).
The
result shows that the value of IVI shared by endemics is highest in the very
high evergreen class (Fig. 4). The
major share of IVI in the very high as well as high evergreen class is by
endemic and nonendemic evergreen; for moderate
evergreen class by nonendemic evergreen and deciduous
trees whereas, for low and very low evergreen classes it is by deciduous trees.
Tree
endemism and their habitat preference
Tree endemism is positively related with
the evergreenness of forest and most of the endemics
recorded in the river basin occurred in the very high evergreen class. The
result of Chandran (1997) revealed that the endemism
including the shared endemism with Sri Lanka increases with evergreenness. It is interesting that the indicator
species of climax evergreen forests like Dipterocarpus
indicus, Dysoxylum
malabaricum, Myristica
malabarica, Myristica
fatua var. magnifica,
Mastixia arborea,
Palaquium ellipticum,
Poeciloneuron indicum
and Vateria indica
were found only in the very high evergreen class (Table 1). More interesting is even in this very
high evergreen class, they occurred in the primary evergreen forests with more
than 90% evergreenness. These species may be called endemics of
climax forests, as they are the species indicating the climax nature of a
forest. Some of these
form the habitat and food plants for the survival of rare and endangered
flagship species like Lion-tailed Macaque Macaca
silenus (Ramachandran
& Joseph 2000) and Great Pied Hornbill Buceros
biornis occurring in this region (Ali et al.
2006).
In addition to very high evergreen class, P.
ellipticum and V. indica
were recorded even in the high evergreen class also but represented by
single individual is exceptional and may be a chance factor. Occurrence of these endemics only in the
very high evergreen class indicates that these species prefer the high
evergreen, dense canopy forests as their habitat. These species have very low ecological
amplitude because of the narrow range of conditions on which their growth
depends and such species may be called as habitat specialist. Any alteration in these habitats
(forests) such as incidence of fire, logging etc is
likely to have an irreparable damage to their existence.
Except Holigarna
grahamii, Holigarna
beddomei and Polyalthia
fragrans all other endemic species are poorly
represented in the high evergreen class.
This indicates that compared to very high evergreen class, these
habitats do not support endemics of high evergreen to flourish. The commonly occurring deciduous tree
species in this class were Terminalia paniculata,
Lagerstroemia microcarpa and Vitex altissima and
most of them are represented by older individuals. These deciduous species probably
appeared in this high-rainfall zone because these forests have a history of
slash and burn cultivation (Chandran 1997). Banning of shifting cultivation led to
the return of the evergreen species and these evergreen species with closed
canopy prevented the regeneration of the more light-loving deciduous trees. Denser canopies and thicker litter
cover in such forests are known to prevent seed germination. This
in turn affect the regeneration of these light seeded deciduous species
(Chandrashekara & Ramakrishnan
1994).
Several
endemics disappeared from moderate evergreen class. The
deciduous endemic Tabernaemontana heyneana was represented by very few individuals. The forests in the low evergreen class
are susceptible to annual fires which seems to be a
major limiting factor for the evergreens and the endemics to come up. Only the fire hardy evergreens Syzygium cumini (Hegde et al. 1998) that can tolerate fire to some extent
and the pioneer evergreen Aporosa lindleyana were recorded. In the very low evergreen class only Tabernaemontana heyneana
and Flacourtia montana had some individuals indicating that,
except these two species, no other endemics have the ability to tolerate and
come up in such conditions. Usually
these forests are also prone to frequent and annual fires. Inspite of
periodic fires and direct sun light (due to canopy openings), presence of Tabernaemontana heyneana
in such forests indicate that they are capable of tolerating the fire, mainly
due to the presence of thick bark and high coppicing ability. This species was also found in the
higher evergreen class, but restricted to canopy gaps and forest edges
only. According to Hegde et al. (1998) T. heyneana
must have existed originally in naturally open habitats within climax forest,
such as on steep escarpments and later might have spread to more open areas. F. montana was also found in all five evergreen
classes but it has maximum occurrence in high evergreen class. It means that as soon as the fire stops
it starts to appear even in the very low evergreen class or other words it may
tolerate fire to some extent so that it occurs even in the deciduous forests.
In
general the endemic tree communities of the Western Ghats are mostly evergreen
species. Very few deciduous
endemics are known to occur in the region like Terminalia
travancorensis, Bauhinia phoenicea
and Tabernaemontana heyneana. The first one is limited to the south of
the Palghat Gap, the second one has wider but sparse
distribution in the deciduous forests of Western Ghats and the third one has a
wider distribution throughout the Western Ghats including the SRB. It is the Tabernaemontana
heyneana that contributed the major share of
endemism in low and very low evergreen class in the river basin.
Table 2. Habitat
preference of different endemic trees in tree layer, shrub layer and herb
layer.
|
Evergreen classes |
Very High |
High |
Moderate |
Low |
Very Low |
||||||||||
Species |
TR |
SH |
HR |
TR |
SH |
HR |
TR |
SH |
HR |
TR |
SH |
HR |
TR |
SH |
HR |
|
1 |
Tabernaemontana heyneana |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
2 |
Flacourtia montana |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
+ |
+ |
+ |
+ |
3 |
Holigarna arnottiana |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
+ |
+ |
4 |
Ixora brachiata |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
+ |
5 |
Knema attenuata |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
6 |
Actinodaphne angustifolia |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
+ |
7 |
Cinnamomum macrocarpum |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
8 |
Diospyros candolleana |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
9 |
Artocarpus hirsutus |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
10 |
Litsea laevigata |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
11 |
Reinwardtiodendron anamallayanam |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
12 |
Beilschmiedia dalzellii |
+ |
+ |
+ |
+ |
|
+ |
+ |
|
|
|
|
|
|
|
|
13 |
Euonymus indicus |
+ |
|
|
+ |
|
+ |
+ |
|
|
|
|
|
|
|
|
14 |
Hopea ponga |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
+ |
+ |
+ |
|
|
|
15 |
Vepris bilocularis |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
+ |
|
|
|
+ |
|
16 |
Garcinia gummigutta |
+ |
+ |
+ |
+ |
+ |
+ |
+ |
|
+ |
+ |
|
|
+ |
|
|
17 |
Sageraea laurifolia |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
+ |
|
|
|
|
|
|
18 |
Diospyros saldanahae |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
19 |
Holigarna grahamii |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
20 |
Polyalthia fragrans |
+ |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
21 |
Holigarna beddomei |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
22 |
Vateria indica |
+ |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
23 |
Drypetes elata |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
24 |
Gordonia obtusa |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
25 |
Holigarna ferruginea |
+ |
+ |
+ |
|
|
|
+ |
|
|
|
|
|
|
|
|
26 |
Palaquium ellipticum |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
27 |
Dimorphocalyx lawianus |
+ |
+ |
|
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
28 |
Garcinia indica |
+ |
|
+ |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
29 |
Hydnocarpus laurifolia |
+ |
|
|
+ |
|
|
|
|
|
|
|
|
|
|
|
30 |
Arenga wightii |
+ |
+ |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
|
31 |
Diospyros paniculata |
+ |
+ |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
|
32 |
Eugenia macrosepala |
+ |
+ |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
|
33 |
Mammaea suriga |
+ |
+ |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
|
34 |
Calophyllum apetalum |
+ |
+ |
+ |
+ |
|
|
+ |
+ |
|
|
|
+ |
+ |
|
+ |
35 |
Aglaia lawii |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
36 |
Diospyros pruriens |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
37 |
Dipterocarpus indicus |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
38 |
Garcinia talbotii |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
39 |
Hopea parviflora |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
40 |
Myristica malabarica |
+ |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
41 |
Poeciloneuron indicum |
+ |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
42 |
Syzygium laetum |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
|
43 |
Syzygium travancoricum |
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
|
44 |
Diospyros angustifolia |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
|
|
|
45 |
Mastixia arborea |
+ |
|
+ |
+ |
|
|
|
|
|
|
|
|
|
|
|
46 |
Myristica fatua var. magnifica |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
|
|
|
47 |
Drypetus confertifolius |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
48 |
Dysoxylum malabaricum |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
49 |
Meiogyne pannosa |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
50 |
Tricalysia apiocarpa |
+ |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
51 |
Blachia denudata |
|
|
+ |
+ |
|
+ |
|
|
|
|
|
|
|
|
|
Total occurrence |
50 |
40 |
42 |
32 |
25 |
23 |
17 |
10 |
9 |
8 |
3 |
5 |
4 |
4 |
6 |
TR -Tree layer; SH - Shrub layer; HR - Herb layer
CONCLUSION
In the SRB the tree endemism is positively related
to evergreenness of the forest. Most of the tree endemics in the river
basin are restricted to very high evergreen class. Out of 51 endemics recorded in the river
basin, 50 occurred in the very high evergreen class and 18 of them were
exclusive to these high evergreen forests. Because of such narrow distribution
they are most vulnerable to extinction.
Hence, priority should be given to their conservation and restoration.
The climax species like Dipterocarpus indicus, Vateria
indica, Poeciloneuron
indicum and, Palaquium
ellipticum are seen only in the very high
evergreen class. Any restoration
efforts for such climax endemic tree species should be restricted to high
evergreen forests. Conservation
priority should be given to the high evergreen forests
as they are the home for most of the endemic trees.
Uttara
Kannada District including part of the SRB was considered as the northernmost
limit for many endemic tree species like Dipterocarpus
indicus, Poeciloneuron
indicum, Hopea
parviflora, and Myristica
fatua var. magnifica
and the highly threatened tree species Semecarpus
kathalekanensis, Syzygium
travancoricum (Chandran
et al. 2008, 2010), and Madhuca bourdillonii; however, M. fatua
var. magnifica, S. kathalekanensis
and S. travancoricum have been recorded from a
Myristica swamp further north of Western Ghats
in Goa (Prabhugaonkar et al. 2014).
Paleoendemics are the indicators of climax forests, and in SRB, such relics of
primary forests can be seen in Kathalekan and Karikan, where Dipterocarpus
indicus is found. Similarly Vateria
indica and Poeciloneuron
indicum were found in Hessige
and Karani, respectively. Conservation priority should be given to
such high evergreen forests as they are the home for
most of the endemics including the paleoendemics. Therefore, habitat preferred by the
endemics should be considered before any restoration programs.
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