reserves. The rocks enriched in organic components are mudstones in Lambir, Miri and Tukau Formations of Middle Miocene-Lower Pliocene age. Significant quantities of Sarawak soil are lithosols, up to 60 per cent, and podsols, around 12 per cent, while abundant alluvial soil is found in coastal and riverine regions. 12 per cent of Sarawak is covered with peat swamp forest. Limestone with well-developed karst topography and cave systems is found scattered from west to east Sarawak, but concentrated in certain regions such as in the Bau district in the west and southwards near the Kalimantan border. There are thirty national parks, among which are Niah with its eponymous caves, the highly developed ecosystem around Lambir Hills, and the World Heritage Site of Gunung Mulu. The last contains Sarawak Chamber, one of the world's largest underground chambers, Deer Cave, the largest cave passage in the world, and Clearwater Cave, the longest cave system in Southeast Asia. Biodiversity Sarawak contains large tracts of tropical rainforest with diverse plant species, which has led to a number of them being studied for medicinal properties. Mangrove and nipah forests lining its estuaries comprise 2% of its forested area, peat swamp forests along other parts of its coastline cover 16%, Kerangas forest covers 5% and Dipterocarpaceae forests cover most mountainous areas. The major trees found in estuary forests include bako and nibong, while those in the peat swamp forests include ramin (Gonystylus bancanus), meranti (Shorea), and medang jongkong (Dactylocladus stenostachys). Animal species are also highly varied, with 185 species of mammals, 530 species of birds, 166 species of snakes, 104 species of lizards, and 113 species of amphibians, of which 19 per cent of the mammals, 6 per cent of the birds, 20 per cent of the snakes and 32 per cent of the lizards are endemic. These species are largely found in Totally Protected Areas. There are over 2,000 tree species in Sarawak. Other plants includes 1,000 species of orchids, 757 species of ferns, and 260 species of palm. The state is the habitat of endangered animals, including the borneo pygmy elephant, proboscis monkey, orangutans and Sumatran rhinoceroses. Matang Wildlife Centre, Semenggoh Nature Reserve, and Lanjak Entimau Wildlife Sanctuary are noted for their orangutan protection programmes. TalangSatang National Park is notable for its turtle conservation initiatives. Birdwatching is a common activity in various national parks such as Gunung Mulu National Park, Lambir Hills National Park,