Himalayan subtropical broadleaf forests
The Himalayan subtropical broadleaf forests is an ecoregion that extends from the middle hills of central Nepal through Darjeeling into Bhutan and also into the Indian States of Uttar Pradesh and Bihar. It represents the east-west-directed band of subtropical broadleaf forest at an altitude of between along the Outer Himalayan Range, and includes several forest types traversing an east to west moisture gradient. Geography. The ecoregion covers an area of and is bisected by the Kali Gandaki River, which has gouged the world's deepest river valley through the Himalayan Range. It forms a  critical link in the chain of interconnected Himalayan ecosystems, where altitudinal connectivity between the habitat types is important for ecosystem function. The soil is composed of alluvium deposited over the ages by the rivers that drain this young mountain range. At lower elevations, the ecoregion is flanked by the Terai-Duar savannas and grasslands. Above , it yields to the Himalayan subtropical pine forests. Climate. Rainfall varies from east to west, but annual rainfall can be as much as . The Himalayas capture moisture from the monsoons that sweep in from the Bay of Bengal, and most of this rainfall is expended  in the eastern Himalayas. Therefore, the western Himalayas are drier, a trend reflected in the timberline that declines from in the east to about in the west. Flora. The ecoregion hosts a broad range of plant communities, based on its complex topography, differing soils, and variations in rainfall from the drier west to the more humid east. Its location on the south slope of the Himalaya allows the intermingling of plants and animals from the Indomalayan and Palearctic biogeographic realms. The main forest types include "Dodonaea" scrub, subtropical dry evergreen forests of "Olea cuspidata", northern dry mixed deciduous forests, dry  Siwalik sal ("Shorea robusta") forests, moist mixed deciduous forests, subtropical broadleaf wet hill forests, northern tropical semi-evergreen forests, and northern tropical wet evergreen forests. Fauna. Several mammals native to the ecoregion are threatened, including the Bengal tiger, Indian elephant, smooth-coated otter, clouded leopard, gaur, Sumatran serow, Irrawaddy squirrel, and particoloured flying squirrel. The endemic golden langur is distributed in a small range and limited to the broadleaf forest north of the Brahmaputra River. The bird fauna is very rich with more than 340 species. The chestnut-breasted partridge is endemic; the globally threatened white-winged wood duck and  five hornbill species are found here. Protected areas. Eight protected areas extend into this ecoregion covering , which is about 7% of the ecoregion's area: Two high-priority tiger conservation units (TCU) extend across adjacent ecoregions: