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Sri
Lanka Dry-Zone Dry Evergreen Forests
Satellite view of the dry forest in northern Sri Lanka
Photograph by USGS
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 harbours 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).
Biome
Tropical and Subtropical Dry Broadleaf Forests
Size
18,700 square miles (48,400 square kilometers) -- about twice
the size of Vermont
Conservation statu
Vulnerable
The Sri Lanka Dry-Zone Dry Evergreen Forests [IM0212] harbour
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 [IM0212] retain their leaves during the dry season. Only
two other ecoregions exhibit this phenology: the small East
Deccan Dry Evergreen Forests [IM0204] and the South-eastern
Indochina Dry Evergreen Forests [IM0210] 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 [IM0212]
are the only viable example of evergreen dry forests in the
bioregion.
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 south-eastern 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).
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 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.
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