Distribution of Tropical Rain Forests in Africa and Asia.

Around 150 to 200 years ago, tropical rain forests stretched as an unbroken green belt over the humid tropics, in three main blocks in the. Amazonian, African and Far-Eastern regions. Today they are greatly reduced and are in a fragmented state. The rain forests of Sri Lanka belong to the Far-Eastern group which includes the rain forests of South and South-East Asia. The centre of this block is the Malayan Archipelago stretching eastward to New Guinea. Although, the rain forests of south-west Sri Lanka share many features common to this group, they also contain elements that are peculiar to themselves alone.The origin of Sri Lankan rain forests . and their unique species composition i.e. a large proportion of endemics, have been explained in relation to the island's geological history. During the Paleozoic era. Sri Lanka was part of the Southern super continent or Gondwanaland. About 140 million years ago this continent began to break up and 55 million years ago, during the mid - Cretaceous period, the fragment known as the Deccan Plate which comprised India and Sri Lanka drifted off towards the equator to collide with the Northern continent of Laurasia. Under equatorial climatic conditions, a tropical community was established on the Dec-can Plate. These conditions however did not remain stable, for continuous fluctuations of climate and sea level in the tropics occurred during the Glacial and Inter-glacial periods. With the submersion of the land connection with the Indian subcontinent 20 million years ago, Sri Lanka separated out as an island. Since then, temporary land connections with the subcontinent have been formed from time to time. The Glacial periods have resulted in alternating climatic conditions of ever-wet and seasonally dry, cool weather prevailing on the island. .As these occurred, rain forests expanded over to the mainland and contracted back into the ever-wet pockets we have today.The rain forest species presently found in Sri Lanka therefore have affinities to Gondwanic flora and fauna as well as to those of the Deccan Plate. While some elements may have been maintained without change, others have evolved into new plants and animals. From a biogeographic point of view therefore the species found in the rain forests of Sri Lanka are of extraordinary interest, a fact which has still not been widely recognized. Together with the rain forests of the Mascarene Islands (Rodriguez, Reunion and Mauritius), East Madagascar, the Seychelles, and the Andamans, the rain forests of Sri Lanka represent* the few surviving links between the rain forests of one major block, (the African) and another (South-East Asian).