Brahmaputra Valley semi-evergreen forests, WWF ecoregion in southern Bhutan.

The Brahmaputra Valley semi-evergreen forests form a 56,700 km² ecoregion across the alluvial plain of the upper Brahmaputra in Assam, with small parts in Arunachal Pradesh, Nagaland, southern Bhutan and northern Bangladesh. The plain lies between the Himalayas and the Lushai hills; in the June–September monsoon the river floods it with up to 300 cm of water. Canopy trees include evergreen Syzygium, Cinnamomum and Magnoliaceae with deciduous Terminalia myriocarpa and Bombax ceiba, and bamboo understory.

The ecoregion's alluvial plain has been farmed for thousands of years, and that long clearance left the original semi-evergreen forest only in patches. In 1997 the WWF identified twelve protected areas, about 2,560 km2 or 5% of the ecoregion, including Manas, Kaziranga and Dibru-Saikhowa. The Rani Vulture Breeding Centre was set up in 2008 in Kamrup district with help from the Jatayu centre at Pinjore.

The valley has been densely populated and farmed for centuries, so the semi-evergreen forest survives only in patches, mostly inside national parks such as Manas, Dibru-Saikhowa and Kaziranga. The pygmy hog and hispid hare, the valley's endemic mammals, live in the grasslands along the riverbanks.

The June-to-September monsoon floods the plain with up to 300 cm of water, so low-lying grassland and riverbank tracks are submerged and access to the core zones of Manas, Dibru-Saikhowa and Kaziranga is by boat or elephant-back. The dry months that follow leave the floodplain easier to cross. The Brahmaputra itself separates many species, so which bank you are on determines what you can see.

This woodland holds one of the world's largest populations of the rare greater one-horned rhinoceros, found today in only a handful of places on Earth. Together with Asian elephants, it represents one of the last places where such large animals coexist.