The Sinharaja Forest Reserve is one of the least disturbed and biologically unique lowland rainforests in Sri Lanka. This forest covers an area of about 11,187 hectares from east to west. The length of the forest is about 21 km and the width from north to south is about 3.7 km. It was declared a Man and Biosphere Reserve (MAB) in 1978 as a representative of the tropical humid evergreen forest ecosystem in Sri Lanka and has been recognized by UNESCO as part of its International Network of Biosphere Reserves. It was declared a national wilderness area in 1988 and, more recently, a World Heritage Site in 1989. It is situated in the lowland humid zone of the south-west of the country in the districts of Ratnapura, Galle and Matara. The average annual temperature in Sinharaja is 23.6 °C. The annual rainfall is more than 2500 mm. Rain is well distributed during the two monsoons; From May to July and from October to December.