Sri Lanka is an island with an extant of 65610 km2 lying off the south eastern corner of the Indian sub continents. Approximately 75% of the island is coastal plain. It referred to as first peneplain covered mostly with isolated hills that are rising up to 600m or more. Inland from the first peneplain to third spread with mountain ranges comprising a South- Central massif which rises to over 2500m msl. There are 103 natural rivers basing which cover 90% of the land area of the country flow to Indian Ocean from all direction of the country.
Sri Lanka has a tropical climate with distinct rainy and dry seasons. The monsoon rains bring the higher percentage of annual rainfall. While inter monsoon and convectional rains also contribute to the annual rain fall significantly. South- west monsoon from May to September bring rains to south western low land and western slope of central highlands. From November to February is the north-east monsoon which brings the heavy rains and cover the dry zone of the country. In between get some convectional and inter monsoon rains with thunders and lightning.
The island is conventionally divided into wet zone, intermediate zone, dry zone and arid zones according to the prevailing climatic condition and vegetation. Climate is the main determinant of natural forest distribution. Tropical rain forest is the climax vegetation of the south west wet zone with wet evergreen forest present at higher altitudes. This zone gets an average annual rain fall about 2500 – 5000ml. The intermediate zones are seasonally dried. Northern and eastern plains have tropical semi-evergreen forest in the dry zone. Annual average rain falls about 2000- 2500 ml . Then the arid zone of the north western and south eastern extremities of the island is covered with tropical thorn forest. This zone gets an annual rain fall about 800 – 1200ml.
Even though Sri Lanka is smaller country in size, biologically most diverse country in Asia. It has been recognized as a biodiversity hotspot of global importance being one of the 250 sites of prime importance for the conservation of the world floristic diversity.