Description
Location and General Description
The Sri Lanka Dry-Zone Dry Evergreen Forests [IM0212] 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 (Deraniyagala 1992).
The ecoregion receives about 1,500-2,000 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-m isolated peak in the central part of Sri Lanka, is the highest point between the central massif and the Western Ghats of India (Jayasuriya 1984).
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 (Gunatilleke and Gunatilleke 1990). 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. (McKay 1973). The dominant grasses in the villus include Cymbopogon spp., Eragrostis spp., Themeda spp., and Imperata spp. (McKay 1973).
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 (Jayasuriya 1984).
Biodiversity Features
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.
The seventy-four mammal species known from the ecoregion include four near-endemic species (table 1).
Table 1. Endemic and Near-Endemic Mammal Species.
Family Species
Cercopithecidae Semnopithecus vetulus
Viverridae Paradoxurus zeylonensis
Muridae Mus fernandoni
Muridae Vandeleuria nolthenii
An asterisk signifies that the species' range is limited to this ecoregion.
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) (IUCN 2000).
Bird richness is greater, with 270 species, of which nine species are near endemic (table 2).
Table 2. Endemic and Near-Endemic Bird Species.
Family Common Name 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.
The spot-billed pelican (Pelecanus philippensis) is a globally threatened species. BirdLife International has included this entire ecoregion within an EBA, Sri Lanka (124) (Stattersfield et al. 1998).
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.
Current Status
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 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
Kudumbigala 40 IV
Yala East Block 1 230 II
Uda Walawe 320 II
Yala 230 I
Kataragama 10 IV
Katagamuwa 10 IV
Wirawila-Tissa 50 IV
Bundala 70 IV
Kalametiya Kalapuwa 10 IV
Maduru Oya Block 1 570 II
Nuwaragala 400 VIII
Nelugala 90 UA
Gal Oya Valley NE 120 IV
Gal Oya Valley 280 II
Sneanayake Samudra 80 IV
Gal Oya Valley SW 120 IV
Sagamam 2 IV
Lahugala Kitulana 170 II
Vavunikulam 20 IV
Madhu Road 250 IV
Kokilai Lagoon 50 IV
Giant's Tank 50 IV
Padaviya Tank 30 IV
Wilpattu Block 1 130 II
Wilpattu North 10 IV
Anaulandewa 310 VIII
Trincomalee Naval Headworks 170 IV
Great Sober Island 1 IV
Mahakandarawewa 10 IV
Anuradhapura 40 IV
Mihintale 7 IV
Hurulu 250 VIII
Seruwila-Allai 140 IV
Somawathiya Block 1 370 II
Tirikonamadu 240 IV
Ritigala 30 I
Minneriya-Giritale 60 IV
Victoria-Randenigala-Rantambe 140 IV
Floodplains 130 II
Polonnaruwa 10 IV
Minneriya-Giritale Block 1 140 IV
Wasgomuwa Lot 1 370 II
Total 6,790
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 [IM0212]. This ecoregion corresponds to MacKinnon's (1997) biounit S13 and overlaps with floristic zones 1 and 2 identified by Ashton and Gunatilleke (1987).
References
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List
Prepared by: Eric D. Wikramanayake and Savithri Gunatilleke
Reviewed by: