Template:Sri Lanka lowland rain forests

Sri Lanka lowland rain forests

Published: May 8, 2014, 1:50 pm

Topics:

Conservation Biology (main) Biodiversity (main) Ecology (main)

Southwest Sri Lanka. Source: Eric Wikramanayake

WWF Terrestrial Ecoregions Collection

The Sri Lanka lowland rainforests occupy the extreme southwestern part of the nation of Sri Lanka, including the coastal zone. This ecoregion is classified within the Tropical and Subtropical Moist Broadleaf Forests biome, and comprises a land area of approximately 12,600 square kilometres. Dutta and Manamendra-Arachchi listed fifty-three amphibian species found in Sri Lanka. This number was a substantial increase from the thirty-five species described by Kirtisinghe in what was the preceding definitive work on the Amphibia of Sri Lanka for almost half a century. But dedicated amphibian surveys have since increased this number to more than 250 frog species (Biodiversity), most of them endemic to the rainforests in the southwestern quarter of the island.

The globally outstanding levels of endemism in the Sri Lanka lowland rainforests are epitomised by this assemblage of frogs.

Location and General Description

The Sri Lanka lowland rainforests represents the tropical rainforests below 1000 metres (m) in elevation in the southwestern quarter of Sri Lanka.

Source: World Wildlife Fund and Encyclopedia of Earth

A continental island, Sri Lanka is separated from the mainland Indian peninsula by the shallow Palk Strait. The island was part of Gondwanaland until the Cretaceous, when, as part of the Deccan Plate, it became detached and drifted northward. The Deccan Plate collided with the Asian mainland-the Southern Laurasian coastline-about 55 million years later. Therefore, the ecoregion harbors several ancient Gondwana taxonomic groups. The island first became separated from the mainland Indian subcontinent during the late Miocene. Since then, climatic changes have interposed drier conditions between the moist forests in southwest Sri Lanka and the Western Ghats in India, the closest other moist forests. Despite the several land bridge connections with the Indian Peninsula since the initial separation, the moist forest and its wet forest-adapted biota have been ecologically isolated.

The May to September southwest monsoon, extended by the inter-monsoonal season before and after the true monsoon, brings more than 5000 millimetres (mm) of rainfall to the ecoregion. Temperatures remain nearly constant, twenty seven to thirty degrees Celsius (^oC), year-round. Convectional winds from the ocean also ameliorate daily temperatures, especially along the coastal areas. Relative humidity is high (80 to 85 percent). The long years of isolation combined with these warm, moist conditions have resulted in the evolution of specialised species found nowhere else on Earth.

The ecoregion partially encircles the central massif, which rises to more than 2500 metres in elevation, and the detached Knuckles Mountain Range to the northeast. These mountains are placed in their own ecoregion, the Sri Lanka montane rainforests. The ecoregion's topography is characterised by deep valleys of the major rivers that radiate from the central mountains. The soils in this lowland wet-zone ecoregion are red-yellow podzolic soils.

The vegetation is influenced primarily by climate, with topography and edaphic conditions contributing secondarily. The lowland wet evergreen forests are characterized by two floral communities: the Dipterocarpus-dominated community and the Mesua-Shorea community. The former is characterised by Dipterocarpus zeylanicus and D. hispidus, with Vitex altissima, Chaetocarpus castanocarpus, Dillenia retusa, D. triquetra, Myristica dactyloides, and Semecarpus gardneri. The canopy of the Mesua-Shorea community consists of Anisophyllea cinnamomoides, Cullenia rosayroana, Mesua ferrea, M. nagassarium, Myristica dactyloides, Palaquium petiolare, Shorea affinis, S. congestiflora, S. disticha, S. megistophylla, S. trapezifolia, S. worthingtoni, Syzygium rubicundum, and a subcanopy of Chaetocarpus castanocarpus, Garcinia hermonii, Syzygium neesianum, and Xylopia championi. Undisturbed forests have four strata, with a main canopy at thirty to forty metres, a sub-canopy at fifteen to thirty metres, a five to fifteen metre high understory, and a sparse shrub layer. Emergent species (Biodiversity) rise above the upper canopy to forty five metres.

Among the distinct habitat types included within the ecoregion are patches of swamp forests closer to the coastlines, although most of these have long been converted to agriculture. Small patches of Avicennia-Rhizophora-Sonneratia-dominated riverine and fringing mangroves line the coastlines, especially near the mouths of the major rivers.

Biodiversity Features

Wiegmann's agama (Otocryptis weigmanni), Sri Lanka Source: Rahula Perera

Almost all of Sri Lanka's endemic flora and fauna are confined to the rainforests in the southwest quarter of the island, where the warm, moist climatic conditions and the longer period of isolation of the wet forest-adapted species have promoted the evolution of endemism and specialization.

For instance, more than sixty percent of the 306 tree species that are endemic to Sri Lanka are found only in the lowland rain forests represented by this ecoregion, and another sixty-one species are shared with the montane rainforests and dry forests. Of the twelve endemic floral genera on the island, eleven are confined to the rainforests. Ninety-eight percent of the fifty-eight species in the family Dipterocarpaceae, the dominant tree family in Asian rainforests, endemic to the rainforests, and these include two endemic genera, Doona and Stemonoporus. An endemic ground orchid, Anoectochilus setaceus, commonly known as the king of the forest or wanaraja, is found only in undisturbed portions of these rain forests. Several other plants have highly localized distributions. Examples include Diospyros oppositifolia, which is confined to the top of a small but species-rich peak known as Hinidumkanda, Stemonoporus moonii, and Mesua stylosa, which are known only from an inland marsh forest in Bulathsinhala, and an aquatic Cyperaceae, Mappania immersa, which is limited to some streams at Sinharaja. Floristically, the lowland and lower hill forests are the biologically richest in Sri Lanka and of all South Asia.

As a small island, Sri Lanka lacks the space to support many of the megavertebrates found on the mainland, although the fossil record indicates that ancestral forms of rhinoceroses, hippopotamuses, and lions once roamed here. Despite the small number of large faunal species (Biodiversity), the ecoregion contains several near-endemic mammals, including one strict endemic (Table 1).

Table 1. Endemic and Near-Endemic Mammal Species.
Family	Species
Soricidae	Suncus montanus
Soricidae	Suncus zeylanicus*
Rhinolophidae	Hipposideros halophyllus
Cercopithecidae	Semnopithecus vetulus
Viverridae	Paradoxurus zeylonensis
Sciuridae	Funambulus layardi
Muridae	Petinomys fuscocapillus
Muridae	Mus fernandoni
Muridae	Vandeleuria nolthenii
(

The two endemic shrews, Suncus zeylanicus and Suncs montanus, are Endangered and Vulnerable, respectively. The Sri Lankan leopard (Panthera pardus kotiya) is considered a threatened genotype. The ecoregion also contains a small population of the Endangered Asian elephant (Elephas maximus). The Vulnerable Grey long-tailed goral (Naemorhedus griseus) also is found in the ecoregion. Unlike the larger elephant populations in the dry-zone ecoregion, this small rainforest population is greatly threatened by habitat loss and fragmentation.

The ecoregion is completely contained within an EBA, Sri Lanka (124). Sixteen avian species are considered near-endemic species, and two are strict endemics (Table 2). The endemic Green-billed coucal and Sri Lanka whistling-thrush (Myiophonus blighi) are classified as Threatened.

Table 2. Endemic and Near-Endemic Bird Species.
Family	Common Name	Species
Columbidae	Ceylon wood-pigeon	Columba torringtoni
Bucconidae	Ceylon grey hornbill	Ocyceros gingalensis
Cuculidae	Red-faced malkoha	Phaenicophaeus pyrrhocephalus
Cuculidae	Green-billed coucal	Centropus chlororhynchus*
Phasianidae	Ceylon spurfowl	Galloperdix bicalcarata
Phasianidae	Ceylon junglefowl	Gallus lafayetii
Corvidae	Ceylon magpie	Urocissa ornata
Turdidae	Spot-winged thrush	Zoothera spiloptera
Sturnidae	White-faced starling	Sturnus senex
Sturnidae	Ceylon myna	Gracula ptilogenys
Muscicapidae	Kashmir flycatcher	Ficedula subrubra
Timaliidae	Brown-capped babbler	Pellorneum fuscocapillum
Timaliidae	Orange-billed babbler	Turdoides rufescens
Dicaeidae	White-throated flowerpecker	Dicaeum vincens*
Capitonidae	Yellow-fronted barbet	Megalaima flavifrons
Psittacidae	Ceylon hanging-parrot	Loriculus beryllinus
Psittacidae	Layard's parakeet	Psittacula calthropae
Strigidae	Chestnut-backed owlet	Glaucidium castanonotum
An asterisk signifies that the species' range is limited to this ecoregion.

Among the other vertebrate groups, two reptiles, the Mugger crocodile (Crocodylus palustris) and the Spineless forest lizard (Calotes liocephalus), are listed as Endangered, as are eight freshwater fish species.

Southern whipping frog (Polypedates longinasus), Sri Lanka. Source: Rahula Perera

Several other taxonomic groups also exhibit high levels of endemism. The rhacophorid frogs, in particular, have undergone a remarkable radiation, and this richness places these rainforests at the apex, in terms of amphibian species numbers per unit area. Many of these species have only limited range distributions, often less than 0.5 square kilometres (km²⁾, and are now limited to the undisturbed habitat fragments. Thus, extinctions surely must have accompanied the widespread habitat destruction in this ecoregion.

Prehistory

Prehistorical human settlement in Sri Lanka is thought to have begun at least 100,000 years ago, with documented paleolithic settlements approximately 35,000 BC at Pahiyangala and somewhat more recently at Batadombalena. Remains of distinctly modern man were found in the caves at Belilena, with evidence that the latter civilisation was likely involved with sedentary agriculture. 

The Yakshas and Nagas are some of the earliest identifiable ancient tribes, with early burial grounds dating to roughly 600 BC. The Anuradhapura Kingdom, somewhat to the north of the subject ecoregion, was known to have existed in Sri Lanka circa 380 BC, with the early rule by Pandukabhaya of Anuradhapura. 

Current Ecological Status

During the past two centuries, nearly all the natural forests in this ecoregion have been cleared for tea, rubber, and coconut plantations, rice paddies, and human settlements. Only about eight percent of the lowland wet forests now remain, as several small, isolated patches in a highly fragmented landscape. Nevertheless, because many of the endemic species in the ecoregion have small areal habitat needs, these patches can provide adequate refuge, if they are effectively protected and managed to ameliorate edge effects and other external threats.

Currently, just about two percent of the ecoregion's intact habitat is protected within five protected areas (Table 3). The most important of these are undoubtedly the Sinharaja Natural Heritage Wilderness Area and Peak Wilderness Sanctuary. The latter extends into the montane rainforest ecoregion. Together, these two protected areas represent the two largest forest patches. However, because most of Sri Lanka's endemic species and species richness lie within the rainforest ecoregions, the current level of habitat protection is inadequate. The Forest Department has also set aside several conservation areas from its portfolio of forest reserves to address conservation gaps. The Sinharaja reserve is contiguous with several forest reserves, namely Morapitiya, Runakanda, Panagala, and Delgoda, that together form the largest forest block, accounting for about forty three percent of the remaining wet-zone forests. Although these reserves will contribute significantly to the overall protected areas system, it is imperative that all remaining habitat patches be conserved to safeguard the remaining beta-diversity. Unless additional protection with effective management is provided, Sri Lanka's most important elements of biodiversity could be lost forever.

Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.
Protected Area	Area (km2)	IUCN Category
Sri Jayewardenepura Bird Sanctuary	30	IV
Sinharaja	100	IV
Telwatte	20	IV
Attidiya Marsh	10	IV
Peak Wilderness [IM0155]	100	IV
Total	260
Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

Types and Severity of Threats

Sinharasa, Sri Lanka (Photograph by Eric Wikramanayake)

Fifty-five percent of Sri Lanka's human population lives in this small ecoregion, which represents less than twenty five percent of the land area. Clearing land for agricultural expansion and settlements to support this population and illegal logging, albeit small-scale, in the remaining forests are the most serious threats to the survival of the endemic species.

Justification of Ecoregion Delineation

Sri Lanka's forests have been divided into two broad climatic sub-regions, the wet zone and the dry zone. In a previous analysis of conservation units of the Indo-Malayan realm, MacKinnon placed the wet-zone forests into a single biounit, Ceylon Wet Zone 02. Here MacKinnon's regional classification is employed as a guiding framework in delineating ecoregions across the Indo-Pacific region. But because one differentiates between lowland and montane forests in delineating ecoregions, the 1000-metre contour is invoked to extract and place the lowland rainforests into a distinct ecoregion, the Sri Lanka lowland rainforests. The ecoregion also overlaps with floristic zones 5, 6, 7, and 11 identified by Ashton and Gunatilleke.

References and Further Reading

• R. A. E. Coningham. 1994. Anuradhapura Citadel Archaeological Project: Preliminary Results of a Season of Geophysical Survey. South Asian Studies 10: 179-188
• Deraniyagala, Siran U.  1996. Pre and Protohistoric settlement in Sri Lanka. International Union of Prehistoric and Protohistoric Sciences. XIII U. I. S. P. P. Congress Proceedings- Forli, 8–14 September 1996. 
• Kennedy, Kenneth A. R., Disotell, T. W., Roertgen, J., Chiment, J., Sherry, J. Ancient Ceylon 6: Biological anthropology of upper Pleistocene hominids from Sri Lanka: Batadomba Lena and Beli Lena caves
• Kalana Maduwage and Anjana Silva. 2012. Hemipeneal Morphology of Sri Lankan Dragon Lizards (PDF). Ceylon Journal of Science. Retrieved 27 September 2012
• Sander, P. Martin. (2012). "Reproduction in early amniotes". Science. 337 (6096): 806–808. doi:10.1126/science.1224301. PMID 22904001.
• Somaweera, Ruchira (2004). Sri Lanka - a world Reptile Hotspot. pdn.ac.lk. University of Peradeniya

• Senarathna, P.M. (2005) Sri Lankawe Wananthara (1st ed.). Sarasavi Publishers. pp. 25–27. ISBN 955-573-401-1.

Additional information on this ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
• To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.

Disclaimer: This article is contains some information that was originally published by, the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

Citation

World Wildlife Fund and C. Michael Hogan (2014) Sri Lanka lowland rainforests. Retrieved from http://editors.eol.org/eoearth/wiki/Sri_Lanka_lowland_rain_forests