threats to biodiversity in Sri lanka
The wet zone districts that harbour more than 60 species of threatened vertebrates and plants, respectively, have a relatively low forest cover. Near-primary forest cover in the wet zone accounts for a little less than 5% of the total land area, what remains are small (less than a km2), isolated patches in a sea of human development. Even the existing protected forests in the wet zone, which harbour high biodiversity, continue to be degraded due to illegal encroachment, and suffer further fragmentation. Typical examples of such forests include the Hakgala Strict Nature Reserve, Peak Wilderness Sanctuary, Kanneliya-Dediyagala-Nakiyadeniya Forest Reserves, Gilimale-Eratne Forest Reserve, Namunukula Forest Reserve, and the Sinharaja World Heritage Site. The implication of habitat loss, especially in the wet zone of the island, is clearly evident by the fact that 18 species of amphibians and 72 species of plants have become extinct during the past two centuries.
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Recent studies on the plant biogeography in south-western hill forests by botanists clearly highlight the conservation significance of these remaining forest patches in the island, where it was revealed that each of them are distinct floristic / bioclimatological forest communities, with ecologically distinct plant species assemblages occurring in the ridges, slopes, and valleys within each forest. The current assessment revealed that a higher number of endemic trees belonging to the Family Dipterocarpaceae are threatened, and these species occupy the canopy and sub-canopy of the above forests. The future survival of the large number of threatened endemic epiphytic orchids also depends on these forest patches in the wet zone.
According to experts who provided information for the present assessment, several species of endemic fauna and flora in the wet zone have already undergone local extinctions during the last three decades, due to the loss of natural habitats. For instance, among the threatened mammals, isolated populations of three arboreal endemic mammals - the Purple-faced Leaf Monkey (Semnopithecus vetulus), the Golden Palm Civet (Paradoxurus zeylonensis) and the Red Slender Loris (Loris tardigradus), have disappeared from several localities in the Western Province, due to loss of tree cover. Among the threatened endemic birds, the Orange-billed Babbler (Turdoides rufescens) has apparently undergone local extinction from some degraded and fragmented forest patches (ie., Nambapana) in the south-western region. Similarly, the endemic Whistling Thrush (Myophonus blighi) is threatened due to extensive clearance and degradation of montane forests through conversion to timber plantations and agriculture.
The current threatened list of mammals includes 10 species of endemic small mammals (6 rodents and 4 shrews). Several scientists have stated that several ecological traits of endemic small mammals render them more susceptible to anthropogenic habitat destruction than the widespread species. A study carried out in the Sinharaja rainforest across habitats representing varying levels of disturbance has clearly demonstrated that endemic rodents and shrews are incapable of utilizing disturbed areas surrounding the natural forest. The latter survey clearly highlights the importance of undisturbed natural forests in the wet zone of Sri Lanka, to sustain the populations of threatened endemic small mammals. Several studies have highlighted the pressures of deforestation and forest fragmentation, on the unique and threatened shrub frogs (Pseudophilautus sp.) restricted to the wet zone of Sri Lanka.
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