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



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9

THE RAFFLES BULLETIN OF ZOOLOGY 2005

THE RAFFLES BULLETIN OF ZOOLOGY 2005 Supplement No. 

12: 9–22

© National University of Singapore



PLANT BIOGEOGRAPHY AND CONSERVATION

OF THE SOUTH-WESTERN HILL FORESTS OF SRI LANKA

I. A. U. N. Gunatilleke, C. V. S. Gunatilleke and M. A. A. B. Dilhan

Department of Botany, University of Peradeniya, Sri Lanka

Email: savnim@slt.lk (IAUNG & CVSG); bdilhan@yahoo.com (MAABD)

(All correspondence to I. A. U. N. Gunatilleke)

INTRODUCTION

The south-west of Sri Lanka, encompassing approximately

20,000 km

2

, is the only aseasonal ever-wet region in the whole



of South Asia (Ashton & Gunatilleke, 1987). This area is of

considerable biogeographic significance to the South and

South-east Asian region for harbouring an exceptional

diversity of a relict biota distinct from that of the Western

Ghats of India (Ashton & Gunatilleke, 1987; Ayyappan &

Parthasarathy, 2001; Gunatilleke & Ashton, 1987; Morley,

2000; van Welzen et al., 2003). The moist rain forests of the

Western Ghats of peninsular India and the aseasonal rain

forests of south-west Sri Lanka are together considered a

refugium of the relict biota of the former Indian plate (Myers

et al., 2000). This plate rafted in isolation from other continents

for a period of over 25 million years in the mid-Paleocene to

late Eocene Epochs (60–35 million years) during which the

evolution of taxa within families and genera continued. Many

of them have subsequently receded in distribution as a

consequence of later competition from Eurasian taxa and

climatic changes accompanying the changing landscape.

These taxa now persist as isolated relicts, vicariants, or

endemics in climatically favourable enclaves like south-

western Sri Lanka and the Western Ghats of peninsular India

(Ashton & Gunatilleke, 1987; Morley, 2000; Swamy et al.,

2000).


In both regions, the natural forests are fast disappearing due

to expanding human populations. In southwest Sri Lanka,

much of the lowland and lower montane rain forests were

cleared in the latter part of the 19

th

 century primarily for



expansion of plantation agriculture and its attendant

anthropogenic influences. Recognising the regional as well

as global significance of these two regions of biogeographic

alliance, southwest Sri Lanka and the Western Ghats of

peninsular India have been declared one of the 25 global ‘Hot

Spots’ of biodiversity as they harbour exclusively in them 0.7

% of the plants and 1.3 % vertebrates listed in the global

literature with their habitats under threat (Myers et al., 2000).

Taking in to consideration the numbers of endemics and

ABSTRACT. – The south-western hill forests of Sri Lanka, harbouring a relict of the Deccan-Gondwana biota,

represent an important element of the Sri Lanka-Western Ghats Biodiversity Hotspot. The tree vegetation of

five of these forests along an altitudinal gradient from 300–1250 m a.s.l was quantitatively analysed. While tree

density over 30 cm gbh increased with increasing altitude, tree size decreased. The canopy, sub-canopy and

understorey tree strata in each forest type were largely dominated by species representing distinct forest

communities along this altitudinal gradient except for a few widespread species. Classification and ordination

analysis of three hill forests along this gradient broadly separated each forest into a distinct floristic/

bioclimatological forest community. These analyses further revealed the presence of ecologically distinct

species assemblages on the ridges, slopes and valleys within each forest type. These results highlight the

presence of both landscape and habitat level floristic heterogeneity in the south-western hill forests of Sri

Lanka, which need to be considered in their conservation management. A high proportion of the tree species

(41%) enumerated in Hinidumkanda, Sinhagala and Tibbottagala are globally threatened. The Rakwana-Deniyaya

hill range in the south-eastern lower montane zone is among the least protected owing to the inadequate

knowledge of their rich biological wealth, which is highlighted in this study. A landscape level integrated

conservation plan for the remaining natural ecosystems along the Gin Ganga (River) from its headwaters in the

Rakwana-Deniyaya hills through the southern Sinharaja forest cluster and the Kanneliya-Hinidumkanda cluster

extending to the Hikkaduwa marine sanctuary seascape at the confluence of the Gin Ganga with the Indian

Ocean is recommended as a model river basin landscape-seascape conservation area for this biodiversity

hotspot.

KEY WORDS. – Sri Lanka, biogeography, conservation, lowland hill forests, biodiversity hotspot.


10

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

endemic species/area ratios for both plants and vertebrates,

and their habitat loss, the Sri Lanka/Western Ghats region is

also ranked among the eight ‘hottest hotspots’ underlining

the global significance of their conservation.

The south-western hills of Sri Lanka are defined as the hills

and hill ranges in the lowland and lower montane aseasonal

climatic regions, to the south and south-west of the central

massif of the island. The rain forests of the south-western

hills are threatened as a result of unabated habitat destruction.

Consequently, the natural vegetation that remains is often

restricted to isolated peaks such as Kalubowitiana (Fig. 1 )

and to the hill ranges such as Kanneliya, Nakiyadeniya,

Dediyagala, Polgahakanda and Hinidumkanda in the coastal

lowlands, the Sinharaja cluster of forests at middle altitudes

(Fig. 2) and the lower montane forests and table-lands of the

Rakwana-Deniyaya hills at the eastern boundary, which abut

the seasonally dry forests to their east (Figs. 3A–C). The

south-western hills are well separated from and located

southwest of the central massif of the island. Abbey Rock

(1300 m) and Gongala (1358 m) represent the highest peaks of

the Rakwana–Deniyaya hills. The south-western coastal hill

ranges commencing immediately east of Kalutara and forming

an arc up to about 30 km wide and parallel to the coast-line

towards the south-east, terminating just inland of Hulandawa

in Matara District, is considered as the floristically richest

area of Sri Lanka and indeed of all South Asia (area 7 of Fig. 6;

Ashton & Gunatilleke, 1987: 275).

Geology. – The main lithotectonic unit of almost the entire

southwest of Sri Lanka is known as the Highland Complex. It

comprises metamorphosed Precambrian sediments and

gneisses of igneous origin (Cooray, 1997). In the extreme

south-western part of this Highland Complex, the crystalline

metamorphic rocks are considered as a separate group, as

they are predominant in granitic gneisses, relatively rare in

the rest of the Highland Complex that extends to the central

massif and north-eastern lower peneplain (Cooray, 1984). The

main metasedimentary rock types in the south-western region

are hypersthene bearing charnockite gneiss of granitic origin,

inter-banded with garnet-sillimanite-graphite gneisses

(schists), cordierite-bearing gneisses and garnet-quartz-

feldspar granulites and gneisses (Cooray, 1988).

A conspicuous geological feature within this region is the

presence of a metabasic (amphibolite and pyroxine granulites)

band of intrusive rocks, extending over 30 km in the SE-NW

direction, known as the ‘Sinharaja basic zone’. This zone is

characterised by a marked aeromagnetic anomaly due to the

high percentage of magnetite present in these basic rocks

(Cooray, 1984).

Land form. – The land form of the Sabaragamuwa hills, of

which the Rakwana-Deniyaya hills form a part, represents a

series of sub-parallel strike ridges running in a SSE-NNW

direction. These ridges have been etched out of a much larger

metamorphic bedrock structure by differential weathering and

erosion of lithologically less resistant beds (Erb, 1984). Heavy

rainfall (>500 cm yr

-1

) from both the south-west and north-



east monsoons has resulted in deep weathering and active

Fig. 1. Kalubowitiana kanda: an isolated lowland hill (735 m) to the

south of the Sinharaja World Heritage Site, surrounded at the base

by paddy fields and home gardens.

Fig. 2. The mid-elevational hill forests (300900 m) in Sinharaja

World Heritage site dominated by Mesua-Shorea (Doona) forest

formations.


11

THE RAFFLES BULLETIN OF ZOOLOGY 2005

erosion almost to base level in the south and south-west

flowing Nilwala, Gin and Kalu rivers. In contrast, the lower

rainfall to the east has resulted in less weathering and erosion,

giving rise to waterfalls and rapids in tributaries of east-

flowing rivers such as the Walawe.

The Rakwana-Deniyaya hills are characterised by a number

of remnants of ancient structurally controlled erosion surfaces,

including the Handapan Ella plateau at 1250 m above sea

level (a.s.l.) and the Thangamale plateau at 1128 m a.s.l. The

Handapan Ella plains have a central undulating valley, several

km

2



 in extent, covered by grasslands and forests. It is

surrounded by a rim of mountain ranges clad in windswept

lower-montane forests (Fig. 4). Across these ranges, the peaks

of Ilumbekanda (1192 m), Beralagala (1385 m), Suriyakanda

(1310 m), Kabaragala I (1234 m) and Kabaragala II (1291 m)

stand out. The Sabaragamuwa hills drain mainly along a series

of more or less parallel strike-, fault- and joint-controlled valleys

running in the SSE-NNW direction (Erb, 1984). Weathering of

these hills has been intense. Consequently, extensive

deposits of talus and colluvial material resulting from active

mass-wasting have formed deep residual soils, characteristic

of this region.



Soils. – The modal soils of the entire south-western region of

Sri Lanka, except certain parts of the coastal plains, are the

Red-Yellow Podzolic soils with low base saturation. They

belong to the modern Soil Taxonomic Order Ultisols and

Suborders Udults and Humults (Panabokke, 1996). The

coastal plains, especially the lower floodplains and river deltas,

Fig. 3. A, lower montane forests (1000 1300 m) in the Eastern

Sinharaja region. The canopy is dominated by hill dipterocarp

species (Shorea trapezifolia and S. gardneri). B, lower montane

forest above Ensalwatta tea plantation. The rocky outcrop to the

far right is Gongala (1358 m), the highest peak in the Rakwana-

Deniyaya hill range. C, land-use pattern in lower montane areas in

Deniyaya. The Lower valleys are predominantly home gardens,

lower and middle slopes are planted with tea, and only the upper

crests remain clothed with natural forests.

A

B

C

Fig. 4. The stepping-stone arrangement of rocks at the top of the

Handapan Ella, a waterfall dried out in the dry season.


12

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

have recently-formed alluvial soils of the Order Entisols

belonging to the Sub Orders Aquents, Fluents and

Psamments. Within the coastal plains, there are isolated

residual hilly areas of Red-Yellow Podzolic soils with soft and

hard laterites (Great Soil Group Plinthudults).

Objectives. – The objectives of this study were to: examine

the variation in structure and floristic composition of the tree

flora in the vegetation of the south-western hill forests of Sri

Lanka with increasing altitude; analyse the community

structure of three hill forests along the altitudinal gradient in

order to provide scientific underpinning for the conservation

of plant communities recognized in the south-western hill

forests; and estimate the number of globally threatened plant

species in the IUCN Red List for Sri Lanka that are harboured

in each study site in order to strengthen the cause for the

conservation of their habitats.

MATERIALS AND METHODS

The information gathered on phytosociological surveys of

four hill forests (Gunatilleke & Gunatilleke, 1984, 1985) and

one plateau have been re-examined in this paper so as to meet

the above objectives. At some of these sites (Hinidumkanda,

Sinhagala, Tibbottagala), quantitative data were collected from

20 randomly placed 0.25 ha paired plots. In the remaining

sites, floristic information were collected from fewer and

smaller number of plots during short visits to these sites. The

geographical locations of these study sites and their altitudinal

ranges are given in Table 1 and Fig. 5.

Study sites. – A brief description of the study sites follows:

Hinidumkanda or Haycock (300–668 m a.s.l.) is a prominent

lowland hill forest located in the hinterland of the south-

western coastal plains. It is a member of the broader

Kanneliya-Nakiyadeniya-Dediyagala cluster of forests, but

separated from it by the valley of the Gin Ganga [ = river]. In

the more interior Sinharaja range of forests, is Sinhagala (550–

730 m a.s.l.), also a lowland hill forest, and east of it is

Tibbottagala (670–900 m a.s.l), which represents the upper

limits of the lowland rain forests. Still further east and up the

altitudinal gradient on the broader south-western landscape,

the Sinharaja range extends to the Rakwana-Deniyaya hills,

Suriyakanda to the north and Gongala and Abbey Rock to

the south. This area encompasses Illumbekanda, Handapan

Ella, Suriyakanda, Thangamale Plains and Gongala, and the

natural vegetation represents lower montane evergreen

forests (Fig.5).

Vegetation Sampling. – In Hinidumkanda, Sinhagala and

Tibbottagala, 5–5.5 ha of primary forest per site were

quantitatively sampled (Table 1). In each site 10–12 locations

along the elevation gradient were selected randomly. At a

given location, two plots, each 0.25 ha in extent, adjacent to

each other, were demarcated, when space was available.

Mostly rectangular plots (25×100 m) were used to keep within-

plot heterogeneity at a minimum. Where space was limiting,

especially near the summits and ridge tops, square plots (50×50

m) were selected. In each plot, all trees > 30 cm gbh were

sampled by measuring their girth at 1.3 m above the ground.

In the lower montane forests at Suriyakanda only 0.25 ha was

sampled and trees > 30 cm gbh were enumerated; at Handapan

Ella, as the trees were all much smaller, only 0.1875 ha was

studied and the lower limit of trees enumerated was 15 cm

gbh, compared to those in the rest of the study sites.

Herbarium material from trees enumerated was collected for

identification to their respective species, based on

Dassanayake et al. (1980–2000).

Multivariate Vegetation Analyses. – A vegetation

classification based on Two Way Indicator Species Analysis

(TWINSPAN) and an ordination based on Detrended

Correspondence Analysis (DCA, DECORANA) using PCORD

version 4 software (McCune & Mefford, 1999) were performed,

with species abundance data of Hinidumkanda, Sinhagala and

Tibbottagala as three representative hill forests along the

altitude gradient of south-west Sri Lanka from 300–900 m a.s.l.

The data were analysed for all three sites together as well as

separately.



Assessment of threatened species. – To assess the threatened

status of the species identified in the study sites, they were

compared with the threatened Sri Lankan plant species

documented in the IUCN Red List (IUCN, 2003).



RESULTS

Structure and floristic composition of tree vegetation. – A

stratigraphic profile of an idealized broad sector of the island’s

floristically rich south-western landscape, from the coastal

region to the eastern boundary of the Rakwana-Deniyaya

hills, depicts its major geomorphology, soil and natural

vegetation features at a glance (Fig. 5). Salient landscape

level differences of these features from the coastal south-

western lowlands to south-central hills in the Rakwana-

Deniyaya range are also summarized in Fig. 5. The structural

features, floristic composition and the dominant species in

the canopy, subcanopy and understorey tree strata of the

forests studied are given in Tables 1 and 2. A comparison of

structural features, such as density (ha

-1

) of the forests shows



a steady increase from the south-western lowland hills to the

lower montane plateau (Table 2), with a concomitant decrease

in tree height and girth. At the lower montane altitude, there

is a preponderance of individuals with girth lower than 30 cm.

In the Handapan Ella plains, the density of individuals

between 15 and 29.9 cm gbh was 3,386 trees ha

-1

. In other



areas, individuals of this size-class were not enumerated and

comparison was therefore not possible.

The dominant tree species in the canopy, subcanopy and

understorey tree strata varied among sites, with the exception

of a few widespread species (Palaquium petiolare,

Anisophyllea cinnamomoides, Myristica dactyloides,

Calophyllum trapezifolium and Garcinia hermonii) (Table

2). In general, the dipterocarp-dominated lower montane

forests shared more species with their lowland counterparts

than with those in the Handapan Ella plateau.



13

THE RAFFLES BULLETIN OF ZOOLOGY 2005

Table 1. Some site details and structural and floristic composition of the tree flora (> 30 cm gbh) of lowland hill forests and lower montane

forests in the southwest of Sri Lanka. Numbers within brackets represent unidentified species.

Site details and

Hinidum-

Sinha-


Tibbotta-

Suriya-


Handapan-

features of vegetation

kanda

gala


gala

kanda


Ella

Geographical location ( ° N, ° E)

6.13, 80.18

6.23, 80.28

6.24, 80.32

6.26, 80.38

6.26, 80.36

Elevation range (m)

300–668

550–730


670–910

950–1310


1250–1300

Area sampled (ha)

5

5.5


5

1.25


0.1875

Density ha

-1

764


769

712


848

2341


Number of species

140 (21)


125 (15)

140 (17)


75 (21)

40 (23)


Endemic species (%)

75

75



60

>50


>50

Fig. 5.


Above: a diagramatic sketch of the relief profile of hills of southwest Sri Lanka, indicating their geology,

soil and forest types. The elevation at the peak of each hill is given along side its name. Below: geographical

distribution of natural forests in southwest Sri Lanka showing their fragmented nature and the approximate

locations (numbers in map) of some of the hill forests.



14

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

Table 2. The dominant species in different canopy, sub canopy and understorey tree strata in hill forests in the southwest of Sri Lanka. (Calo.

= Calophyllum, S. gard. = Shorea gardneri, Syzyg.= Syzygium, Elaeoc. = Elaeocarpus).

*

 = species endemic to Sri Lanka. 



**

 = subspecies

endemic to Sri Lanka. L/LH = lowland/lower montane; RF = rain forest.

Hill forest studied

Forest type

lowland


lowland

lowland/lower-

lower

lower


(hill) RF

(hill) RF

montane RF

montane RF

montane RF

Vegetation community



Diptero-

Mesua-

Calo.-

S. gard.-

Syzyg.-

carpus

Shorea

Shorea

Calo.-

Calo.-

(Doona)

Cullenia

Elaeo.-

 Canopy and Sub-canopy dominants:



Dipterocarpus zeylanicus (Dipterocarpaceae)

*

+



Chaetocarpus castanocarpus (Euphorbiaceae)

+

Cyathocalyx zeylanica (Annonaceae)

+

Palaquium petiolare (Sapotaceae)

*

+



+

Anisophyllea cinnamomoides (Rhizophoraceae)

*

+



+

+

Myristica dactyloides (Myristicaceae)

+

+

+



Mesua nagassarium (Clusiaceae)

**

+



Mesua ferrea (Clusiaceae)

*

+



Shorea worthingtonii (Dipterocarpaceae)

*

+



Shorea affinis (Dipterocarpaceae)

*

+



Cullenia rosayroana (Bombacaceae)

*

+



Cullenia ceylanica (Bombacaceae)

*

+



Calophyllum trapezifolium (Clusiaceae)

*

+



+

+

Shorea trapezifolia (Dipterocarpaceae)

*

+

+



Shorea zeylanica (Dipterocarpaceae)

*

+



Shorea gardneri (Dipterocarpaceae)

*

+



Hydnocarpus octandra (Flacourtiaceae)

*

+



Elaeocarpus glandulifer (Elaeocarpaceae)

*

+



Axinandra zeylanica (Crypteroniaceae)

*

+



Palaquium laevifolium (Sapotaceae)

*

+



Syzygium revolutum (Myrtaceae)

+

Syzygium micranthum (Myrtaceae)

*

+

Syzygium cordifolium (Myrtaceae)



*

+

Garcinia echinocarpa (Clusiaceae)

+

Agrostistachys coriacea (Euphorbiaceae)

*

+



 Understorey Tree Dominants:

Gyrinops walla (Thymelaeaceae)

+

+



Garcinia hermonii (Clusiaceae)

*

+



+

+

Xylopia championii (Annonaceae)

*

+

+



Dillenia triquetra (Dilleniaceae)

+

Humboldtia laurifolia (Fabaceae)

+

Diospyros insignis (Ebenaceae)

+

Fahrenheitia zeylanica (Euphorbiaceae)

+

Strobilanthes spp. (Acanthaceae)

+

Bamboo sp. (Poaceae)



+

Hinidumkanda

300

 668 m


Sinhagala

550


 730 m


Tibottagala

(*Ecotone) 670 



900 m


Suriyakanda 950 

1050 m


Handapan Ella

1250


 1300 m


15

THE RAFFLES BULLETIN OF ZOOLOGY 2005

Among the lowland hill forests sampled, the number of

tree species enumerated was comparable in Hinidumkanda

and Tibbottagala, but lower in Sinhagala. Their numbers

declined progressively in the lower montane forests, again

partly due to the lower girth limit of 30 cm selected for

comparison among sites. Interestingly, the number of

endemic woody species was highest in the lowland forests

and decreased with altitude.

The canopy/sub canopy layer. – The most abundant

species at Hinidumkanda were Dipterocarpus zeylanicus

(Dipterocarpaceae), Palaquium petiolare (Sapotaceae),

Cyathocalyx zeylanica (Annonaceae), Chaetocarpus

castanocarpus (Euphorbiaceae), Anisophyllea

cinnamomoides (Rhizophoraceae) and Myristica

dactyloides (Myristicaceae) (Table 2). However, both the

structure and the abundant species around the peak of

Hinidumkanda differed from those of the middle and lower

elevations (Gunatilleke & Gunatilleke, 1984). Cullenia



rosayroana (Bombacaceae), Myristica dactyloides,

Stemonoporus canaliculatus (Dipterocarpaceae)

dominated the canopy, subcanopy and the understorey

tree layer of the summit vegetation, respectively.

Endangered species like Diospyros oppositifolia

(Ebenaceae) and Schumacheria angustifolia (Dilleniaceae)

are restricted to the summit of Hinidumkanda. This hill

forest represents the Dipterocarpus and Vitex-Dillenia

(Wormia)-Chaetocarpus-Anisophyllea communities in de

Rosayro’s forest classification (de Rosayro, 1950).

Sinhagala, unlike Hinidumkanda, is dominated by the Mesua-



Shorea (Doona) association, which is the climax forest

community in the mid-elevational lowland wet evergreen (rain)

forests of Sri Lanka (de Rosayro, 1950; Gaussen et al., 1966;

Greller & Balasubramanium, 1993). The species characteristic

of the ridge plots in Sinhagala were Mesua nagassarium and

M. ferrea (Clusiaceae), Humboldtia laurifolia (Fabaceae),

Shorea worthingtoniiS. affinisS. cordifolia, S. disticha

(Dipterocarpaceae) and Palaquium laevifolium (Sapotaceae).

At middle and lower elevations of this hill forest, the most

abundant canopy species were Anisophyllea cinnamomoides

(Anisophylleaceae), Dillenia triquetra (Dilleniaceae), Shorea

congestiflora (Dipterocarpaceae) and Campnosperma

zeylanica (Anacardiaceae). The highest diversity of genus

Shorea among the sites sampledrepresented by five species,

was recorded in this hill forest.

In the lower montane ever-wet forests of Tibbottagala (670 –

900 m a.s.l), the most abundant canopy and subcanopy

species were Calophyllum trapezifolium (Clusiaceae), Shorea

trapezifolia (Dipterocarpaceae), Palaquium petiolare

(Sapotaceae), Anisophyllea cinnamomoides (Anisophyll-

eaceae) and Myristica dactyloides (Myristicaceae) (Table 2;

Gunatilleke & Gunatilleke, 1985). The latter two species are

also abundant in the two lower-elevation forests (Table 2).

In Suriyakanda (950–1050 m a.s.l.), the lower montane rain

forests were dominated by Shorea gardneri (Dipterocarp-

aceae), Calophyllum trapezifolium (Clusiaceae) and Cullenia

spp. (Bombacaceae). Similar forest types have been observed

in sites abutting the tea estates in Rakwana-Deniyaya hills.

These forests represent the Shorea (Doona)-Cullenia-

Calophyllum community of the lower montane notophyllous

evergreen dipterocarp rain forest type of Greller &

Balasubramanium (1993).

In Handapan Ella plateau (1250–1300 m a.s.l.), a forest

resembling the lower montane notophyllous evergreen mixed

rain forest of Jayasuriya et al. (1993) and Greller &

Balaubramanium (1993) dominated by the Syzygium-

Calophyllum-Eleocarpus association was observed. This

climatically and edaphically influenced vegetation on the

plateau was short-statured, sometimes exposed to mist and

during the dry months of the year to strong desiccating winds.

It is heterogeneous in its floristic composition, harbouring

elements from lowland and lower-montane rain forests and to

a lesser degree those from the upper-montane forests. Among

the common canopy tree species recorded in plots as well as

in general field collecting were those of Syzygium (Myrtaceae),

Semecarpus (Anacardiaceae), Memecylon (Melastomataceae),

Symplocos (Symplocaceae), Palaquium (Sapotaceae),

Calophyllum and Garcinia echinocarpa (Clusiaceae).

However, the dominant forest species of Handapan Ella

plateau on shallow soils with impeded drainage were not

shared by those of any other forest type examined in this

study (Table 2). This forest type may be an edaphically

influenced variant in shallow soils. Interspersed with the lower

montane rain forests of Handapan Ella and Thangamale plains

and beyond them at Ensalwatta and Beverly estates (although

to a lesser extent) are grasslands, quaking bogs and marshes,

each with their own characteristic biodiversity, which remain

poorly studied to-date.

Understorey Vegetation.– Among the most abundant

understorey tree species were Garcinia hermonii and



Gyrinops walla (Thymelaeaceae) in the lowland hill forests

of Hinidumkanda. In the entire Sinharaja range Garcinia



hermonii and Xylopia championii (Annonanceae) dominated

the undersorey stratum based on the Important Value Indices

(Gunatilleke & Gunatilleke, 1985). Diospyros insignis

(Ebenaceae) and Fahrenheitia zeylanica (Euphorbiaceae)

dominated the understorey of the lower montane forests in

Suriyakanda (Table 2).

On the Handapan Ella plains, the members of Rubiaceae and

Acanthaceae (Strobilathes spp.) were frequent in the

understorey. Bamboo species along with those of Eriocaulon

and Osbeckia, common also in the open grasslands near rocky

outcrops, extend into the forest interior in some areas. On the

plains as well as its outer and inner forested rim an

exceptionally rich orchid flora, some rare and endangered

elsewhere in the island, is present. The rare and cryptic root

parasite Christisonia (Orobanchaceae), only visible when in

flower, is locally abundant on the forest floor in a few areas.

No less than 55 species of orchids, some rare and threatened,

as well as probable new species of Loranthaceae,

Hymenophyllaceae, Lycopodiaceae, Gesneriaceae and

Eriocaulaceae have also been reported from Handapan Ella

and Ensalwatta forests (Suranjan Fernando, pers. comm.).

Three main streams that flow through the plains converge on



16

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

a rocky substratum at the north-eastern edge giving rise to a

waterfall, overlooking the Deepdene estate and Rakwana-

Kalwana road down below. On this escarpment, either side of

the water fall, is an extensive stand of Loxococcus rupicola

(an endemic and monotypic genus), a palm species

characteristic of rocky steep habitats (Fig. 6).



Multivariate analyses. – In the TWINSPAN classification

using all 62 plots from the three hill forest sites (Fig. 7), the

first division based on the indicator species Cullenia

ceylanica and Bhesa zeylanica clumped the 22 Sinhagala

plots and the 20 Tibbottagala plots as group 1 (mid-elevational

and lower montane forests) and all 20 Hiniduma Kanda plots

as group 2 (coastal lowland hill forest) based on the indicator

species Cyathocalyx zeylanicaVitex altissima and

Calophyllum moonii. In further divisions of group 1, 10 of

the Tibbottagala plots, representing those in the high plateau

and the valley, grouped together and the remaining 10 with

the 22 Sinhagala plots. Subsequent divisions of the latter

group separated the Tibbottagala slope plots, from the

Sinhagala valley plots in one branch and the Sinhagala ridge

and upper slope plots in the opposite branch. The successive

divisions of the Hinidumkanda plots in group 2 separated the

valley plots, ridge plots and the upper and lower slope plots

into four clusters. The dendrogram (Fig. 7) gives the details

of the clusters, the indicator species and the Eigen values at

each level of division. By comparing the results of the

TWINSPAN analyses and ordination, the divisions in the

classification were ecologically meaningful at level 4 where

plot clusters in valleys, slopes, ridges summits and plateaux

in respective hill forest separated out (Figs. 7, 8).

The groups of plots in each of the three hill forests

separated out in the two-dimensional ordination (Fig. 8).

Those groups in each study site that emerged in the

classification fall in close proximity to each other, and away

from plots in the other two study sites, with one exception,

where the Sinhagala plots on the ridge and upper slopes

clustered adjacent to the Tibbottagala plots on steep

slopes. In a given site the greatest separation among plots

along these two axes is shown by the Tibbottagala plots,

suggesting that this site has more community diversity

than either the Hinidumkanda or Sinhagala forests. Within

each site, finer scale clustering into ridge, slope and valley

plots were evident from both the ordination and

classification (Figs. 7, 8). The multivariate analyses done

for each site separately showed results similar to that

obtained in the analyses of all three sites considered

together, and is therefore not detailed here.

Globally Threatened species. – In the three study sites,

Hinidumkanda, Sinhagala and Tibbottagala, that were

quantitatively sampled with greater intensity than the other

two sites, 224 woody species were recorded (Table 3). By

comparing these species with those reported in the IUCN

Red List, their threatened status was examined. There are 290

globally threatened Sri Lankan species in the 2003 IUCN Red

List (IUCN, 2003). Among them, 78 are Critically Endangered,

73 are Endangered, 129 are Vulnerable and the remaining 10

belong to the Lower Risk, Extinct and Data Deficient

categories. In the three hill sites studied, 118 (41%) of these

species were recorded in the following categories: 31 Critically

Endangered, 16 Endangered, 66 Vulnerable, and 4 Lower Risk.

The data for individual sites (Table 3; Gunatilleke &

Gunatilleke, 1991) show that the number of threatened species

at Hinidumkanda is 91, which ranks highest, followed by

Sinhagala with 83 and Tibbottagala with 68; the number of

threatened species restricted to each of these sites is 26, 8

and 4, respectively.

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