Sri Lanka dry-zone dry evergreen forests
The Sri Lanka Dry-Zone Dry Evergreen Forests harbor one of Asia's largest and most viable Asian elephant (Elephas maximus) populations and a large protected area system designed specifically for elephant conservation.
Therefore, the ecoregion provides one of the best opportunities to conserve Asia's largest vertebrate over the long-term.
Unlike most other dry forests, the trees in the Sri Lanka Dry-Zone Dry Evergreen Forests retain their leaves during the dry season. Only two other ecoregions exhibit this phenology: the small East Deccan Dry Evergreen Forests and the Southeastern Indochina Dry Evergreen Forests in the Indochina bioregion. Because the evergreen dry forest ecoregion in the east Deccan Plateau is small and has lost most of its intact habitat, the Sri Lanka Dry-Zone Dry Evergreen Forests are the only viable example of evergreen dry forests in the bioregion.
Location and General Description
The Sri Lanka Dry-Zone Dry Evergreen Forests represent the tropical dry forests throughout most of the island of Sri Lanka, except for the southwestern quarter, the central mountain range, and the Jaffna Peninsula in the extreme north.
The island's geological roots date back to the Cretaceous period when, as part of the Deccan Plateau, it detached from Gondwanaland and drifted north to collide with the northern Eurasian continent about 50 million years later. Therefore, the ecoregion harbors elements of the ancient Gondwana biota. The island then became separated from the Deccan Plateau during the late Miocene about 20 million years later. Since that time, there have been several land bridges that allowed species exchanges between the island and the mainland until the final separation during the Pleistocene.
The ecoregion receives about 1,500-2,000 millimeters (mm) of annual rainfall in the December to March northeast monsoon but is mostly dry the rest of the year. Topographically, the ecoregion is flat, except for scattered inselbergs and isolated low hills. Ritigala, a 766-meter isolated peak in the central part of Sri Lanka, is the highest point between the central massif and the Western Ghats of India.
Tropical dry forests cover most of the ecoregion, but within the ecoregion there are a number of distinct habitat types (of sub-regional extent). These include patches of submontane savanna and grassland-known locally as talawa-especially along the eastern and southeastern slopes of the central massif. In the northeast, lowland grasslands, locally known as villus, are associated with the floodplains of the river systems. These grasslands provide critical water and fodder for herbivores during the dry season.
Most of this ecoregion was settled and cultivated until about 500 years ago; therefore, the forest is secondary. However, several patches of old-growth forests remain and are included within protected areas (e.g. Wasgomuwa National Park and parts of Ruhuna National Park).
The evergreen dry forests are dominated by Manilkara hexandra, Chloroxylon sweitenia, Drypetes sepiaria, Feronia limonia, Vitex altissima, Syzygium spp., Drypetes sepiaria, and Chukrasia tabularis, with the scrub and regenerating forests characterized by Bauhinia racemosa, Pterospermum suberifolium, Cassia fistula, and Dichrostachys cineria. Acacia thorn scrub grows in disturbed areas.
The talawa savannas are characterized by Terminalia chebula, T. belerica, Pterocarpus marsupium, Butea monosperma, Careya arborea, Anogeissus latifolia, Phyllanthus embilica, and Zizyphus spp.. The dominant grasses in the villus include Cymbopogon spp., Eragrostis spp., Themeda spp., and Imperata spp..
Ritigala, the isolated hill in central Sri Lanka, is a hotspot of endemic species within this ecoregion with several endemic plants such as Madhuca clavata.
Compared with Sri Lanka's rain forests, this ecoregion does not contain very high levels of endemism. Nevertheless, it harbors one of Asia's largest elephant populations, estimated at 2,500 to 4,000 animals. The large protected area system that was designed using the elephant as a focal species provides an excellent chance for the long-term conservation of this endangered species.
|Table 1. Endemic and Near-Endemic Mammal Species.|
|An asterisk signifies that the species' range is limited to this ecoregion.|
The seventy-four mammal species known from the ecoregion include four near-endemic species (Table 1).
Several of the ecoregion's mammals are also listed as threatened: the endangered Asian elephant, the Sri Lankan genotype of the common leopard (Panthera pardus kotiya), and the vulnerable sloth bear (Melursus ursinus), purple-faced leaf monkey (Semnopithecus vetulus), and slender loris (Loris tardigradus).
|Table 2. Endemic and Near-Endemic Bird Species.|
|Bucconidae||Ceylon grey hornbill||Ocyceros gingalensis|
|Cuculidae||Red-faced malkoha||Phaenicophaeus pyrrhocephalus|
|Phasianidae||Ceylon junglefowl||Gallus lafayetii|
|Phasianidae||Ceylon spurfowl||Galloperdix bicalcarata|
|Turdidae||Spot-winged thrush||Zoothera spiloptera|
|Timaliidae||Brown-capped babbler||Pellorneum fuscocapillum|
|Capitonidae||Yellow-fronted barbet||Megalaima flavifrons|
|Psittacidae||Ceylon hanging-parrot||Loriculus beryllinus|
|Psittacidae||Layard's parakeet||Psittacula calthropae|
|An asterisk signifies that the species' range is limited to this ecoregion.|
Bird richness is greater, with 270 species, of which nine species are near endemic (Table 2).
The spot-billed pelican (Pelecanus philippensis) is a globally threatened species. BirdLife International has included this entire ecoregion within an Endemic Bird Area, Sri Lanka (124).
Viable populations of the freshwater and mugger crocodiles (Crocodylus porosus and C. palustris, respectively) are found along the rivers and estuaries and have also adapted to the numerous ancient reservoirs that formed part of the extensive irrigation system. Two other large lizards, the water monitor (Varanus salvator)-the second largest lizard in the world-and the Bengal monitor (V. bengalensis), which are persecuted and hunted throughout most of their ranges, have found a safe haven in this ecoregion.
About three-quarters of this ecoregion has been deforested; however, extensive areas of contiguous, intact forest remain in the north and north central area. Thirty-eight protected areas cover 7,842 square kilometers (km2), or 17 percent of the ecoregion area (Table 3). This represents the largest proportion of intact forests that are included within the protected area systems of the dry forest ecoregions in the Indo-Pacific region.
|Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.|
|Protected Area||Area (km2)||IUCN Category|
|Ruhuna (Yala) Block 1||1,030||II|
|Yala East Block 1||230||II|
|Maduru Oya Block 1||570||II|
|Gal Oya Valley NE||120||IV|
|Gal Oya Valley||280||II|
|Gal Oya Valley SW||120||IV|
|Wilpattu Block 1||130||II|
|Trincomalee Naval Headworks||170||IV|
|Great Sober Island||1||IV|
|Somawathiya Block 1||370||II|
|Minneriya-Giritale Block 1||140||IV|
|Wasgomuwa Lot 1||370||II|
|Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.|
Two of these protected areas complexes-Yala/Ruhuna and Wilpattu national parks-exceed 1,000 km2 in area, and several other reserves form contiguous complexes that exceed 500 km2. Many of these larger reserves and reserve complexes contain elephant populations that can contribute significantly to a regional conservation program.
Types and Severity of Threats
The primary overarching threats are from deforestation caused by agriculture, resettlements, and small-scale logging. Encroachment into protected areas, several of which lack adequate protection and management, also poses important threats that warrant attention. Overall, however, the protected area system is extensive enough to conserve the ecoregion's biodiversity, given effective management. The cultural and religious taboos against killing and hunting wildlife-most of the country is Buddhist-have served well to protect wildlife relative to the rest of Asia.
Justification of Ecoregion Delineation
The dry zone has been commonly used as a distinct bioclimatic zone in Sri Lanka. We used MacKinnon's (1997) map of original forest cover to separate the dry evergreen forests of Sri Lanka from the wet-zone moist forests and represented the former in the Sri Lanka Dry-Zone Dry Evergreen Forests. This ecoregion corresponds to MacKinnon's (1997) biounit S13 and overlaps with floristic zones 1 and 2 identified by Ashton and Gunatilleke (1987).
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.
- World Wildlife Fund Homepage
- Deraniyagala, S.U. 1992. The prehistory of Sri Lanka. An ecological perspective. Part I. Department of Archeological Survey. Govt of Sri Lanka. ISBN: 9559159003
- Jayasuriya, A.H.M. 1984. Flora of Ritigala strict natural reserve. The Sri Lanka Forester. XVI:61-155
- Gunatilleke, I.A.U.N. and C.V.S. Gunatilleke. 1990. Distribution of floristic richness and its conservation in Sri Lanka. Conservation Biology. 4:21-31
- McKay, G.M. 1973. Behavior and ecology of the Asiatic elephant in southeastern Ceylon. Smithsonian Contributions to Zoology. 125. Smithsonian Institution Press. Washington D.C.
- IUCN. 2000. 2000 IUCN Red list of threatened species. IUCN Red List of Threatened Species. Viewed November 2000. The IUCN Species Survival Commission and the International Union for Conservation of Nature and Natural Resources (IUCN & The World Conservation Union).
- Stattersfield, A. J., M. J. Corsby, A. J. Long, and D. C. Wege. 1998. Global Directory of endemic bird areas. Cambridge, UK: Birdlife International.
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