Nepal is a landlocked central Himalayan country in South Asia. Nepal has a diverse geography, including fertile plains, subalpine forested hills, and eight of the world's ten tallest mountains, including Mount Everest, the highest point on Earth. Nepal is commonly divided into three physiographic areas: Mountain, Hill and Terai. These ecological belts run east–west and are vertically intersected by Nepal's major, north to south flowing river systems. The dramatic differences in elevation found in Nepal result in a variety oF biomes, from tropical savannas along the Indian border, to subtropical broadleaf and coniferous forests in the Hill Region, to temperate broadleaf and coniferous forests on the slopes of the Himalaya, to montane grasslands and shrublands and rock and ice at the highest elevations. At the lowest elevations is the Terai-Duar savanna and grasslands ecoregion. These form a mosaic with the Himalayan subtropical broadleaf forests, which occur from 500 to 1,000 metres (1,600 to 3,300 ft) and include the Inner Terai Valleys. Himalayan subtropical pine forestsoccur between 1,000 and 2,000 metres (3,300 and 6,600 ft). Above these elevations, the biogeography of Nepal is generally divided from east to west by the Gandaki River. Ecoregions to the east tend to receive more precipitation and to be more species-rich. Those to the west are drier with fewer species. From 1,500 to 3,000 metres (4,900 to 9,800 ft), are temperate broadleaf forests: the eastern and western Himalayan broadleaf forests. From 3,000 to 4,000 metres (9,800 to 13,100 ft) are the eastern and western Himalayan subalpine conifer forests. To 5,500 metres (18,000 ft) are the eastern and western Himalayan alpine shrub and meadows. In a land once thickly forested, deforestation is a major problem in all regions, with resulting erosion and degradation of ecosystems.