Nepal is a land of geographical extremes, ranging from near sea level elevations in the southern Terai to the world's highest mountains. The country contains a variety of ecosystems, treeless sub alpine pastures and dense fir forests of the high valleys, oak and rhododendron woods of the middle hills, and tall sal forests of the south. Along the southern borders of Nepal are preserved much of the lowland jungles and grasslands that once covered this part of the sub continent. Here one can see birds and mammals found nowhere else, Although animal habitat has been somewhat depleted as a result of agriculture, deforestation and other causes, through Nepal's extensive and effective park and reserve system, the country still has more varied flora and fauna than any other area in Asia.
Tropical Deciduous Monsoon Forest
This includes the Terai plains and the broad flat valleys or Duns found between hill ranges. The dominant tree species of this area are Sal (Shorea robusta), sometimes associated with Semal (Bombax malabricum), Asna (Terminalia termentosa), Dalbergia spp. and other species, and Pinus roxburghi occuring on the higher ridges of the Churia hills, which in places reach an altitude of 1,800 meters.Tall coarse two meter,high elephant grass originally covered much of the Dun valleys but has now been largely replaced by agricultural settlement. This tropical zone is Nepal's richest area for wildlife, with gaurs, wild buffalo Four species of deer, tiger, leopard and other animals, Rhinoceros, swamp deer and hog deer are found on the grasslands and two species of crocodile and the Gangetic dolphin inhabit the rivers.
Subtropical Mixed Evergreen Forest
This includes the Mahabharat Lekh which rises to a height of about 2,400 meters and comprises the outer wall of the Himalayan range. Great rivers such as the Karnali, Narayani, and Sapta Koshi flow through this area into the plains of the Terai. This zone also includes the so called "middle hills", which extend northward in a somewhat confused maze of ridges and valleys to the foot of the great Himalaya. Among the tree species characteristic of this region are Castenopsis indicia in association with Schima wallichi, and other species such as Alnus nepalensis, Acer oblongum and various species of oak and rhododendron, which cover the higher slopes where deforestation has not yet taken place. This zone is generally poor in wildlife. The only mammals which are at all widely distributed are wild boar, barking deer, serow, ghoral and bear. Different birds are also found in this zone .
Temperate Evergreen Forest
Northward on the lower slopes and spurs of the Great Himalaya, oaks and pines are the dominant species up to an altitude of about 2,400 meters Above these are found dense conifer forest of Picea, Tsuga, Larix and Betula spp. Abies and Betula are usually confined to higher elevations, with Betula typically marking the upper limit of the tree line. At about 3,600 to 3,900 meters rhododendron, bamboo and maples commonly mingle with the conifers. The compositions of the forest varies considerably, with coniferous predominating in the west and eracaceous in the east. The wildlife of this region includes the Himalayan bear, serow, ghoral, barking deer and wild boar, with the Himalayan tahr sometimes being seen on steep rocky faces above 2,400 meters. The red panda is among the more interesting of the smaller mammals found in this zone ; it appears to be fairly well distributed in suitable areas of the forest above 1,800 meters. The rich and varied avifauna of this region includes several spectacular and beautiful pheasants, including the Damphe pheasant, Nepal's national bird.
Subalpine and Alpine Zone
Above the tree line, rhododendron, juniper scrub and other procumbent woody vegetation may extend to about 4,200 meters where they are then succeeded by a tundra?like association of short grasses, sedge mosses and alpine plants wherever there is sufficient soil. This continues up to the lower limit of perpetual snow and ice at about 5,100 meters. The mammalian fauna is sparse and unlikely to include any species other than the Himalayan marmot, mouse hare, tahr, musk deer, snow leopard and occasionally blue sheep. In former times, the wild yak and great Tibetan sheep could also be sighted in this region and it is possible that a few may still be surviving in areas such as Dolpa and Humla. The bird life at these altitudes includes several interesting species such as the lammergeyer, snowcock, snowpartridge, chough and bunting, with redstarts and dippers often seen along the streams and rivulet.