Plant biogeography and conservation of the south-western hill forests of sri lanka I. A. U. N. G



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DISCUSSION

Forest types represented. – In the past many attempts have

been made to classify the forests of Sri Lanka using floristic

(de Rosayro, 1950; Gaussen et al., 1966), bioclimatic and

physiognomic (Greller & Balasubramaniam, 1993; Koelmeyer,

1957) characteristics (Table 4). The floristic analysis of the

present study reveals that the Hinidumkanda vegetation

represents both the Dipterocarpus and Vitex-Dillenia

(Wormia)-Chaetocarpus-Anisophyllea communities of the

wet evergreen forest climax formation of de Rosayro’s

classification and the lowland mesophyllous evergreen

dipterocarp rain forests of Greller & Balasubramaniam. The

Sinhagala vegetation, on the other hand, represents the



Mesua-Doona  (Shorea) community of de Rosayro; but in

Greller & Balasubramaniam’s classification, the distinction

between these coastal and inland lowland forest communities

of de Rosayro has not been made. The presence of several

abundant species in Tibbottagala (670 – 900), which are also

found in both Hinidumkanda (300–668 m) and Suriyakanda

(950–1050 m), suggests that the Tibbottagala vegetation

represents an ecotone between lowland and lower-montane

forests of this region. In Tibbottagala, Mesua nagassarium

is replaced by Calophyllum trapezifolium as one of the most

abundant canopy species.

Floristically, the Suriyakanda vegetation conforms to the

submontane evergreen forests of Koelmeyer (1957), Doona-

Calophyllum-Syzygium series of Gaussen et al. (1966), and

Fig. 6. A stand of Loxococcus rupicola (Araceae) on steep rocky

slopes near Handapan Ella.


17

THE RAFFLES BULLETIN OF ZOOLOGY 2005

Fig. 7. Classification (Two-Way Indicator Species Analyses) of 62 plots sampled in the hill forests of Hinidumkanda (plots Y1 Y10, Z1

Z10), Sinhagala ( A11  A21, B11  B21) and Tibbottagala ( A33  A42, B33  B42) in southwest Sri Lanka, using abundance data of each

species. The indicator species and the eigen values at each division are also given.

the lower montane notophyllous evergreen dipterocarp rain

forests of Greller & Balasubramaniam (1993). de Rosayro has

not recognised this as a distinct forest type in his

classification. The Handapan Ella vegetation, characterized

by the absence of Shorea gardneri, corresponds to the lower

montane notophyllous evergreen mixed rain forests of Greller

& Balasubramaniam (1993). This distinct forest type has been

overlooked in other forest classifications. The floristic data

in our study support the forest classifications based on

distinct floristic assemblages although no single classification



7

4

4

Plots: Sinhagala 22, 

Hiniduma 20 and 

Tibottagala 20

17

A41


B41

A42


B42

A37 


B37 

A38 


B38 

B35 


A36  

A17 


B17 

A18 


B18

A12      

A13,B13 

A14,B14  

A15,B15 

A16,B16 


A19,B19

A11 


B11  

B12 


A20 

B20 


A21 

A21


A39

B39 


A40

B40  


12

A33


B33

A34


B34

A35


A36

4

2

10

11

6

10

5

7

Y10 


Z10

Y7

Z7 



Y8

Z8 


Y9

Z9

Y5



Z5 

Y6

Z6 



Z4 

Y1  


Z1 

Y2

Z2 



Y3

Z3 


Y4

4

2

6

20 Plots

6

15

32

8

42 Plots

Upper 


slope

plots


Valley

plots


Sinhagala

Summit


plots

Lower 


slope

plots


Hinidumkanda

Tibbottagala

High 

plateau


plots

Valley


plots

Steep 


slope

plots


Slope

plots


Valley

plots


Ridge

plots


0.302

0.22


Chionanthus

albidiflora  1

Dillenia

retusa  1 

Mesua

nagassarium 1

Gyrinops 

walla  1

0.384


0.322

0.402


0.386

0.290


0.422

0.366


0.37

Cyathocalyx  zeylanica  1 

Vitex altissima 1

Calophyllum moonii  1

Cullenia ceylanica 1

Bhesa ceylanica 1

Nothopegia

beddomei 1

Agrosti-

stachys 

coriacea 1

Humboldtia 

    laurifolia 1

Palaquium 

    laevifolium 1

Shorea 

   worthingtonii 1

0.383


Palaquium       1

canaliculatum    

Garcinia   sp. 1

Axinandra 

zeylanica 1

Garcinia                     

     quaesita  1             

Campnosperma          

     zeylanicum  2        

Palaquium                 

     petiolare  4          

Timonius

 flavescens 1

Less steep

slopes & +ive

border-line

plots


18

Gunatilleke et al.: South-western Hill Forests of Sri Lanka



Sinhagala

plots

Tibbottagala

plots

Hinidumkanda 

plots

High plateau

plots

Valley


plots

Less steep 

slope plots 

Borderline plots

             -ve 

+

ve          



Lower

slope


plots

Upper 


Slope

Plots


Valley

plots


Summit 

plots


valley  

plots


Ridge &  steep 

slope plots 

Steep slope 

plots


Axis 2 

Axis 1 


Fig. 8. Ordination (Detrended Correspondence Analysis) on the 62 plots sampled in the hill forests of Hinidumkanda (plots Y1Y10, Z1

Z10), Sinhagala (A11A21, B11B21) and Tibbottagala (A33 A42, B33B42) in southwest Sri Lanka, using abundance data of each

species. The plot distributions in the ordination diagram are indicated by the plot number used in field sampling.

Table 3. Numbers of species in the south-western hill forests of Hinidumkanda (Hinidum.), Sinhagala and/or Tibbottagala (Tibbott.) in

different categories of the 2003 IUCN Red List. CR = critically endangered, EN= endangered, VU = vulnerable, LR/cd = lower risk:

conservation dependent; RIRL, NIRL = number of species recorded and not recorded in the Red List, respectively.

Study Sites Sampled

CR

EN



VU

LR/cd


Sub Total:

Sub Total:  Total

RIRL

NIRL


Hinidumkanda only

6

4



16

26

42



68

Sinhagala only

3

2

3



8

6



14

Tibbottagala only

1

1

2



4

11



15

Hinidumkanda & Sinhagala

3

2

10



15

4



19

Hinidumkanda & Tibbottagala

1

2

1



4

13



17

Sinhagala & Tibbottagala

8

6

14

12

26



Hinidum., Sinhagala & Tibbot.

9

5



28

4

46



19

65

 Total in all three sites



31

16

66



4

117


107

224


 Individual Study Sites

Total in Hinidumkanda

19

13

55



4

91

78



169

Total in Sinhagala

23

9

47



4

83

41



124

Total in Tibbottagala

19

8

37



4

68

55



123

19

THE RAFFLES BULLETIN OF ZOOLOGY 2005

recognised all the different forest communities encountered

in our survey. Interestingly, the six forests quantitatively

sampled by us, along this altitudinal gradient some 80 km

direct east from the south-west coast represent five different

forest types.

This study emphasizes the need for a quantitative analysis of

a much larger database including those from other forests in

the south-western region of Sri Lanka in order to identify

distinct floristic communities facilitating a review the existing

forest classifications in a more objective manner recognising

at the same time micro-scale habitat variations to capture the

habitats of localised endemics.

Floristic variation. – Both TWINSPAN and DCA of pooled

plots of the three hill forests revealed the presence of distinct

floristic communities akin to those described in literature along

the altitudinal gradient at landscape level. Separation of plots

in each of the three hill forests along axes 1 and 2 in the DCA

provides quantitative evidence for the presence of distinct

forest communities in the coastal lowland (Hinidumkanda),

interior mid-elevational (Sinhagala) and lower montane/

ecotone (Tibbottagala) hill forests confirming previous

qualitative classifications of the vegetation. The only

exception was the overlap of four steep slope plots (A39,

B39, A40 and B40) in Tibbottagala with the ridge and steep

slope plot cluster in Sinhagala (Fig. 8), owing to the higher

proportion of species shared between them.

Both analyses indicated a finer scale separation of floristically

recognizable local communities in valleys, lower and upper

slopes and high plateau or summit plots in each hill forest.

However, the plots on the ridges, summits or plateaux, slopes

and valleys in each hill forest separated from their counterparts

in both analyses suggesting their distinctiveness. This

provides evidence for spatial heterogeneity and ecological

differentiation of tree species along the finer-level climatic

and topographic gradients and consequently, provides the

scientific underpinning for conservation management

planning of these forests.

The presence of distinct species assemblages on the ridges,

slopes and valleys, along the altitudinal gradient of the Mesua-

Shorea (Doona) community in hilly topography has been

further supported by census data of the 25 ha Forest Dynamics

Plot (FDP) in Sinharaja, where all free standing woody plants

> 1 cm dbh have been enumerated and plotted on a contour

map (Gunatilleke et al., 2004). This FDP plot spans an elevation

range of only 150 m; yet it depicts eight different habitats

based on topography, convexity and slope. Further, at least

for some canopy dominant taxa, the ecophysiological

adaptations of their seedlings to micro-climatic gradients of

light, moisture and soil nutrients along the topographic

gradient during early establishment and recruitment phases

have been shown (Ashton et al., 1995; Gunatilleke et al.,

1996,1997,1998). All these studies, including the present study,

show habitat specialization of plants along small scale

gradients in the hill forests of Sri Lanka, which has important

Table 4. The south-western hill forests of the present study according to different  forest classifications in the literature.

Forest classification of

Hill forests

sampled in

de Rosayro

Koelmeyer

Gaussen et al.

Greller & Balasub-

present study

(1950)

(1957)


(1966)

ramaniam (1993)

Hinidumakanda

Dipterocarpus

Tropical wet



Doona-Dipterocarpus

Lowland mesophyllous

community

evergreen



Mesua series

evergreen dipterocarp rain

forests

forests


Vitex-Dillenia-

Chaetocarpus-

Anisopyllea

community

Sinhagala

Mesua-Doona

Tropical wet



Doona-Dipterocarpus

Lowland mesophyllous

community

evergreen



Mesua series

evergreen dipterocarp rain

forests

forests


Tibbottagala

Mesua-Doona

Tropical wet



Doona-Dipterocarpus

Lowland mesophyllous

community

evergreen



Mesua series

evergreen dipterocarp rain

forests

forests


Suriyakanda

Not recognized

Submontane

Doona-Dipterocarpus

Lower montane mesophyllous

evergreen

Syzygium series

evergreen dipterocarp rain

forests

forests


Handapan Ella

Not recognized

Not

Not


Lower montane mesophyllous

recognized

recognized

evergreen mixed rain forests



20

Gunatilleke et al.: South-western Hill Forests of Sri Lanka

conservation implications considering the fact that many of

these species are relict endemics.



Localized distribution of threatened species. – Comparison

of the species in the IUCN Red List (Table 3) in the three

quantitatively sampled forests, shows that 43% of the 224

species identified were found only in one of the three sites,

depicting very localized distribution of these species,

particularly in Hinidumkanda with as many as 68 species.

With 169 tree species it is also the richest among the study

sites sampled. Among the endangered species in the IUCN

Red list that are highly restricted in their distribution and

enumerated in Hinidumkanda are Shorea dyeri, S. lissophylla



and Diospyros oppositifolia. The results of this study also

show that tree species richness decreases with altitude,

Hinidumkanda ranking highest and Handapan Ella the lowest,

the latter probably being also due to the smaller extent of

forest studied. On the other hand most, if not all, studies in

Sri Lanka, including our own, have so far failed to investigate

the diversity of the herbaceous and lower plant floras,

components of the vegetation known to increase in diversity

with altitude.

The remaining forests in southwest Sri Lanka represent only

a small fraction of less than 9% of their original extent. Today

even these are also highly fragmented, most small in extent,

with receding boundaries due to a multitude of human impacts.

Hinidumkanda is one of the few protected areas that represent

the Dipterocarpus community. High point-endemism and high

habitat specialization in Sri Lanka’s rain forest species

demands that the remaining forests in its south-western

quarter, however disturbed or fragmented they are, need to

be conserved with a sense of urgency. Among these are the

representatives of the Dipterocarpus community in the coastal

belt and hill forests and high plateaux of the Rakwana-

Deniyaya hill range representing the lower montane

notophyllous evergreen mixed/Dipterocarp rain forests.

Compared to these forests types, the Mesua-Doona

community is better protected in the Sinharaja and the

Kanneliya-Dediyagala-Nakiyadeniya groups of forests.



Conservation issues. – In response to criticism mounted

against the first Forestry Master Plan for Sri Lanka (Anon.,

1986) and subsequent assessment of the environmental

implications of the Forestry Sector Development Project,

an Environmental Management component was included

in this project (Anon., 1997). This component was

mandated to evaluate all remaining natural forests in the

country with respect to their importance for biodiversity,

in terms of ecosystem and species diversity, and their value

for soil and water conservation. This study, commonly

referred to as the National Conservation Review (NCR),

inventoried and analysed the data of selected groups of

plant and animal species in 204 forests in the island. Among

the recommendations of the NCR, those related to the

present study are, (a) all montane forests should be strictly

protected by upgrading the status of proposed reserves

to conservation forests, or even national heritage

wilderness areas; and (b) the largest remaining forests in

the wet zone should be designated in their entirety as

conservation forests, inter alia, Sinharaja complex (a group

of 13 forests including Handapan Ella Plains, Diyadawa

and Dellawa) and broader Kanneliya, Nakiyadeniya and

Dediyagala (KDN) complex so that the long-term

conservation of biodiversity could be ensured.

The biological value of the forests in close proximity to the

northern, western and southern borders of the Sinharaja World

Heritage Site (WHS) has been recognised and identified as

conservation forests, based on recommendations of the NCR.

However, forests along the eastern perimeter of the Sinharaja

WHS, where part of this study has focused (Suriyakanda and

Handapan Ella), have yet to receive the attention they merit.

These areas were not adequately surveyed for their biological

wealth even during the NCR. With respect to plants, they

harbour an exceptionally diverse herbaceous and epiphytic

flora including orchids, balsams, ferns, bryophytes, lichens,

fungi & algae, a component of the vegetation in all

ecosystems, which was not studied by the NCR and for that

matter, has almost entirely been neglected in Sri Lankan

biodiversity surveys.

Therefore, relying entirely on the NCR as the source of

quantitative scientific information for purposes of

conservation planning could lead to serious omissions of

areas rich in herbaceous and epiphytic plants which are at

greater threat of extinction considering their sensitivity to

habitat alteration and habitat size decrease. Consequently,

due to the dearth of adequate scientific information,

particularly with respect to the rich flora of herbaceous and

lower-plant taxa, some areas of the Rakwana-Deniyaya hills

are not included in the current protected area system. Hence,

they are in imminent danger of being degraded further through

poaching, timber and firewood harvesting, cardamom

cultivation, illicit gem prospecting and other activities inimical

to biodiversity.

Forest degradation and destruction. – The threats to the

many fragile ecosystems of the Handapan Ella plains appear

to be extensive, particularly in the grasslands and stream

banks, where thousands of gem pits (most ~1 m deep) have

been dug over the years. These illegal encroachers have caused

extensive damage to the forest by cutting wood and poaching

animals in this fragile ecosystem.

In early 2004 there was an even more sinister threat to the

relict forest fragments adjoining the eastern boundary of the

Sinharaja WHS, despite repeated requests and

recommendations made to annex them to the Sinharaja WHS

to increase its conservation value. Instead, these state-owned

forest lands were blocked out and sold for tea and cardamom

cultivation. This irresponsible act, amidst public protests,

including those of scientists familiar with the biological wealth

of the region and its conservation value, has irreparably

damaged this fragile ecosystem, critically endangering some

of the threatened animal and plant taxa exclusive to the

Rakwana-Deniyaya hills.

The forests near the south-eastern boundary of the

Sinharaja WHS abutting the Sinharaja Division of the


21

THE RAFFLES BULLETIN OF ZOOLOGY 2005

Ensalwatta Plantation and also Beverley and Manikkawatta

Estates are on long-term lease to plantation companies.

These appear to be relatively free of any encroachments

for gem prospecting and wood-cutting. The forests

surrounding the Sinharaja Division of the Ensalwatta

Plantation represent Shorea gardneri (Sinhala: Rath Dun)

and Shorea trapezifolia (S: Yakahalu Dun) tree formations

at their very best (Figs. 9, 10). These magnificent forest

stands, traversed by streams and spectacular waterfalls,

harbour abundant wildlife, including a small herd of

elephants, and are an important watershed for the

downstream communities.

Similarly, forests in the highest peaks of the Rakwana-

Deniyaya hills, viz., Abbey Rock (1300 m) and Gongala (1358

m), those near Panilkanda and Aninkanda estates, Naigala,

Kabaragala, Beralagala, Suriyakanda and Kurulugala deserve

to be conserved. Apart from a few explorations for taxonomic

and preliminary ecological study purposes, their conservation

value is yet to be evaluated and documented (Jayasuriya et

al., 1993). Several animal species endemic to the Rakwana-

Deniyaya hills and new to science have been collected from

this region (Bahir & Ng, 2005; Manamendra-Arachchi &

Pethiyagoda, 2005; Pethiyagoda & Manamendra-Arachchi,

1998).

Extension of the current eastern boundary of the Sinharaja



WHS to include these forests within an appropriate protected-

area category is proposed once again (Gunatilleke & Ashton,

1987), as an urgent measure to conserve their rich biodiversity.

The presence of a small herd of elephants in the Rakwana-

Deniyaya hills is an important criterion for establishing a

wildlife reserve in this region. Their migratory routes need to

be studied in order to demarcate and establish habitat corridors

connecting the surrounding forests, particularly to the north

of the Rakwana-Deniyaya hills. As a dwindling population of

elephants similar to that inhabiting the Peak Wilderness area,

a conservation management plan for wet zone elephants

should also be considered. The role of the elephant in the

functioning of these complex rain forests is virtually unknown.

Such a study would especially benefit nature-based tourism

in this region.

The issues highlighted in this paper should be addressed

coherently with a sense of urgency, before the next wave of

‘development’ overwhelms Sri Lanka. Conservation planning

for Sri Lanka’s south-western region should not be done

piece-meal or on a short-term basis, but at landscape level

that takes long-term impacts into consideration. Appropriate

corridors and buffer zones including multi-species home

gardens, where appropriate, could be used to link the different

ecosystems and forest types in this region.

The present study provides sound evidence that the south-

western hills and, the Rakwana-Deniyaya range of lower

montane forests in particular, indeed possess high

conservation value. However, they have hitherto remained

relatively unprotected owing to their biological and ecological

value not having been adequately assessed in previous

biological surveys. We hope that this study will serve as a

stimulus for demarcating such high-priority conservation

landscapes (both protected and yet unprotected) along the

Gin Ganga basin from its headwaters in the Gongala area

through southern Sinharaja, KDN complex and Hinidumkanda

and remaining mangroves, together with the Hikkaduwa

Marine sanctuary seascape beyond its confluence with the

Indian Ocean at Gintota as an integrated model river basin

landscape-seascape conservation area. Where feasible,

linking of neighbouring forest areas through restoration

corridors with already available research experience for this

region Gunatilleke (1999) is also strongly recommended. The

stratigraphic profile accompanying the map of the south-west

Sri Lanka in Fig. 5 provides some directions for the initial

identification of the relevant areas for this exercise.

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