Yarlung Tsangpo arid steppe


The Yarlung Zambo arid steppe ecoregion covers the river valley of the Yarlung Tsangpo River on the southern edge of Tibet. The river runs parallel to the northern borders of Nepal, Bhutan and India, between the Himalayas to the south and the Tibet Plateau to the north. The river valleys are the most populated areas of Tibet, putting pressure on wildlife. The area ranges from cold desert in the west to steppe shrub land in the east; the few trees are in the lowest river valleys to the east.

Location and description

The Yarlung Tsangpo runs west to east for along the north slope of the Himalayas, but south of the Transhimalaya ranges of the Gangdise Shan and Nyenchen Tanglha Mountains. The ecoregion mostly follows the river valley and short tributary valleys, including the area north to Lhasa. Yamdrok Lake, one of the largest lakes of the Tibetan Plateau is in the region, and at Lhasa is an urban impoundment of water now protected as the Lalu Wetlands National Nature Preserve.

Climate

The climate of the valleys of the ecoregion have a Subarctic climate, dry winter. This climate is characterized by mild summers and cold winters having monthly precipitation less than one-tenth of the wettest summer month. Precipitation in the ecoregion is 200–500 mm/year, increasing from west to east. The valleys also benefit from the drying and warming effects of the katabatic wind.

Flora and fauna

Vegetation in the region changes from west to east, as the river valley gently descends from cold desert, through steppe and deciduous shrub areas, to some areas of confer-rhododenron forest in the east. The temperate slopes above the valley floors in the middle of the ecoregion are steppe and shrub communities, with species of feather grass, fountain grass, needlegrass, and other grasses and shrubs. Above 4,400 meters, vegetation grades into cold steppe species of feather grass and shrubs such as shrubby cinquefoil and honeysuckles. Above 5,000 meters, some areas of stable soil support species of Kobresia sedges, and cushion plants.