Nepal's environment has suffered the effects of agricultural encroachment, deforestation and consequent soil erosion, and contamination of the water supply. Between the mid-1960s and the late 1970s, forestland declined from 30% to 22% of the total area, mainly because of the felling of timber for firewood, which supplies over 90% of Nepal's fuel requirements. Moreover, it is estimated that erosion causes the loss of about 240 million cu m of topsoil each year.
All of Nepal's forests were nationalized in 1957, but reforestation efforts have been minimal. A forest conservation program, begun in 1980, includes the establishment of village tree nurseries, free distribution of seedlings, and provision of wood-burning stoves of increased efficiency. By 1985, however, deforestation averaged 324 sq mi per year, while reforestation was only 4,000 hectares (9,900 acres) per year. An additional4.4% of forest and woodland were lost between 1983 and 1993. The FAO estimates that at the present rate of depletion, the forests will be virtually wiped out by 2015.
Air and water pollution are significant environmental problems in Nepal. According to United Nations sources, the nation produces 18,000 tons of carbon monoxide and 3,300 tons of hydrocarbons per year. Roughly one-third of the nation's city inhabitants and two-thirds of all rural dwellers do not have pure water, and the use of contaminated drinking water creates a health hazard. Untreated sewage is a major pollution factor: the nation's cities produce an average of 0.4 million tons of solid waste per year.
In 2001, 28 of Nepal's mammal species and 27 of its bird species were endangered, as were 7 plant species. Species classified as endangered in Nepal include the snow leopard, tiger, Asian elephant, pygmy hog, great Indian rhinoceros, Assam rabbit, swamp deer, wild yak, chir pheasant, and gavial.