Sri Lanka lowland rain forests

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Southwest Sri Lanka (Photograph by Eric Wikramanayake)

Dutta and Manamendra-Arachchi listed fifty-three amphibian species from Sri Lanka. This was a substantial increase from the thirty-five species-groups described by Kirtisinghe in what was the 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, most of them endemic to the rain forests in the southwestern quarter of the island.

The globally outstanding levels of endemism in the Sri Lanka Lowland Rain Forests are epitomized by this assemblage of frogs.

Location and General Description

The Sri Lanka Lowland Rain Forests represents the tropical rain forests below 1,000 meters (m) in elevation in the southwestern quarter of Sri Lanka.

caption Source: WWF

A continental island, Sri Lanka is separated from the 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 intermonsoonal season before and after the true monsoon, brings more than 5,000 millimeters (mm) of rainfall to the ecoregion. Temperatures remain nearly constant, 27-30 degrees Celsius (oC), year-round. Convectional winds from the ocean also ameliorate daily temperatures, especially along the coastal areas. Relative humidity is high (80-85 percent). The long years of isolation combined with these warm, moist conditions have resulted in the evolution of specialized species found nowhere else on Earth.

The ecoregion partially encircles the central massif, which rises to more than 2,500 m, and the detached Knuckles Mountain Range to the northeast. These mountains are placed in their own ecoregion, the Sri Lanka Montane Rain Forests. The ecoregion's topography is characterized by deep valleys of the major rivers that radiate out of 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 dominated 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 30-40 m, a sub-canopy at 15-30 m, a 5-15 m understory, and a sparse shrub layer. Emergent species rise above the upper canopy to 45 m.

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

caption Lizard (Otocryptis weigmanni), Sri Lanka (Photograph by Rahula Perera)

Almost all of Sri Lanka's endemic flora and fauna are confined to the rain forests 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 60 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 61 species are shared with the montane rain forests and dry forests. Of the twelve endemic floral genera on the island, eleven are confined to the rain forests. Ninety-eight percent of the fifty-eight species in the family Dipterocarpaceae-the dominant tree family in Asian rain forests-are endemic to the rain forests, 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 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 species, 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

An asterisk signifies that the species' range is limited to this ecoregion.

The two endemic shrews, Suncus zeylanicus and Suncus 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). Unlike the larger elephant populations in the dry-zone ecoregion, this small rain forest population is greatly threatened by habitat loss and fragmentation.

The ecoregion is completely contained within an EBA, Sri Lanka (124). Sixteen birds 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 considered 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.

caption Tree frog (Polypedates longinasus, Sri Lanka (Photograph by 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 rain forests 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 kilometers (km2), and are now limited to the undisturbed habitat fragments. Thus, extinctions surely must have accompanied the widespread habitat loss in this ecoregion.

Current 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 8 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 habitat needs, these patches can provide adequate refuge if effectively protected and managed to ameliorate edge effects and other external threats.

Currently, just about 2 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 rain forest 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 rain forest ecoregions, the current level of 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 43 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 will 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

caption 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 25 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. We used MacKinnon's regional classification as a guiding framework in delineating ecoregions across the Indo-Pacific region. But because we differentiated between lowland and montane forests in delineating ecoregions, we used the 1,000-m contour to extract and place the lowland rain forests into a distinct ecoregion, the Sri Lanka Lowland Rain Forests. The ecoregion also overlaps with floristic zones 5, 6, 7, and 11 identified by Ashton and Gunatilleke.

Additional information on this ecoregion

 

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth may have edited its content or 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.

 

 

 

Glossary

Citation

Fund, W. (2014). Sri Lanka lowland rain forests. Retrieved from http://www.eoearth.org/view/article/156230

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