fast-flowing rivers have carved out deep gorges in the lower mountain areas. The forests of the central Bhutan mountains consist of Eastern Himalayan subalpine conifer forests in higher elevations and Eastern Himalayan broadleaf forests in lower elevations. The Woodlands of the central region provide most of Bhutan's forest production. The Torsa, Raidak, Sankosh, and Manas are Bhutan's main rivers, flowing through this region. Most of the population lives in the central highlands. In the south, the Shiwalik Hills are covered with dense Himalayan subtropical broadleaf forests, alluvial lowland river valleys, and mountains up to around above sea level. The foothills descend into the subtropical Duars Plain, which is the eponymous gateway to strategic mountain passes (also known as dwars or dooars; literally, "doors" in Assamese, Bengali, Maithili, Bhojpuri, and Magahi languages). Most of the Duars is in India, but a -wide strip extends into Bhutan. The Bhutan Duars is divided into two parts, the northern and southern Duars. The northern Duars, which abut the Himalayan foothills, have rugged, sloping terrain and dry, porous soil with dense vegetation and abundant wildlife. The southern Duars have moderately fertile soil, heavy savanna grass, dense, mixed jungle, and freshwater springs. Mountain rivers, fed by melting snow or monsoon rains, empty into the Brahmaputra River in India. Data released by the Ministry of Agriculture showed that the country had a forest cover of 64% as of October 2005. Climate Bhutan's climate varies with elevation, from subtropical in the south to temperate in the highlands and polar-type climate with year-round snow in the north. Bhutan experiences five distinct seasons: summer, monsoon, autumn, winter and spring. Western Bhutan has the heavier monsoon rains; southern Bhutan has hot humid summers and cool winters; central and eastern Bhutan are temperate and drier than the west with warm summers and cool winters. Biodiversity Bhutan signed the Rio Convention on Biological Diversity on 11 June 1992, and became a party to the convention on 25 August 1995. It has subsequently produced a National Biodiversity Strategy and Action Plan, with two revisions, the most recent of which was received by the convention on 4 February 2010. Animals Bhutan has a rich primate life, with rare species such as the golden langur. A variant Assamese macaque has also been recorded, which is regarded by some authorities as a new species, Macaca munzala. The Bengal tiger, clouded leopard, hispid hare and the sloth bear