Sinharaja Forest Reserve is situated in the south-west lowland wet zone of Sri Lanka. Most of the area was originally declared a forest reserve on 1875 under the Waste Lands Ordinance and notified in the Ceylon Government, whereas the rest was notified a proposed forest reserve in the early 20th century. Sinharaja Forest Reserve, comprising the existing and proposed forest reserves, was declared a biosphere reserve in 1978.
This narrow strip of undulating terrain consists of a series of ridges and valleys. Two main types of forest can be recognized: remnants of Dipterocarpus forest occur in valleys and on their lower slopes; secondary forest and scrub occur where the original forest cover has been removed by shifting cultivation and in other places the forest has been replaced by rubber and tea plantations. Mesua-Doona forest is the climax vegetation in most of the reserve. Of Sri Lanka's 830 endemic species, 217 trees and woody climbers are found in the lowland wet zone. Other rare endemics are the palm, the latter being restricted to Sinhagala. A variety of plants of known benefit to man are present, of which palm (for jaggery, a sugar substitute), wewal, cardamom, dun (for varnish and incense) and weniwal (for medicinal purposes) are used intensively by villagers.
Endemism is high, particularly for birds, mammals and butterflies. Threatened mammals are leopard and Indian elephant. Birds considered to be endangered or rare are Sri Lanka wood pigeon, green-billed coucal, Sri Lanka white-headed starling, Sri Lanka blue magpie, ashy-headed babbler and red-faced malkoha. Of interest is the presence of the Sri Lanka broad-billed roller. Reptiles and amphibia include the python, which is vulnerable, and a number of endemic species. Noteworthy species include the rarest of all agamids on the island, the rough-nose horned lizard and a rare endemic microhylid. Threatened freshwater fish are combtail, smooth-breasted snakehead, black ruby barb, cherry barb and red-tail goby. Sri Lankan five-bar sword, which is considered to be very rare, is not uncommon in Sinharaja at certain times of the year.
The Sinharaja region has long featured in the legends and lore of the people of Sri Lanka. Its name, literally meaning lion (sinha ) king (raja ), perhaps refers to the original 'king-sized or royal forest of the Sinhalese', a people of the legendary 'lion-race' of Sri Lanka, or to the home of a legendary lion of Sri Lanka.
There are two villages within the south-west of the reserve, and about 52 families live in the north-western sector. At least 20 other settlements occur on the periphery, an unknown number of which have been illegally established on state land without approval from the relevant authorities.
Sinharaja Forest Reserve is the last viable remnant of Sri Lanka's tropical lowland rainforest; over 60% of the trees are endemic and many of these are rare; and there are 21 endemic bird species as well as a number of rare insects, reptiles and amphibians.