(Last Updated on : 21/10/2013)
The Brahmaputra Valley semi-evergreen rain forests in India are an integral part of India's ecosystem. These forests were historically considered as some of the most productive areas in the Indian Subcontinent bioregion. This eco-region lies along the alluvial plains of the Brahmaputra River that flows through the state of Assam and West Bengal in India. The valley has been densely settled by humans and cultivated for thousands of years, because of the eco-region's high productivity. The eco-region harbours an impressive biological diversity in the small fragments of habitat that lie scattered throughout. Some of the few remaining viable populations of India like the Asian elephants and the world's largest population of the greater one-horned rhinoceros can be found in these forests.
The Brahmaputra Valley semi-evergreen rain forests in India are located along the upper Brahmaputra River plains. Though most of the forests lie within the eastern Indian state of Assam, some small sections extend into the neighboring states of Arunachal Pradesh and Nagaland, as well. The eco-region represents the area where the northward-migrating Deccan Peninsula first made contact with the Eurasian continent during the early Tertiary period. It also represents a gateway for species exchanges between the typically Indian and Malayan faunas. There are several species that inhibit in both sides of the wide Brahmaputra River. While the species like golden langur, hispid hare, and pygmy hog are limited to the north bank of the river, the species like hoolock gibbon and stump-tailed macaque can be found only on the south bank.
The annual rainfall in the Brahmaputra Valley semi-evergreen rain forests in India ranges between 1,500-3,000 millimeters, depending on the topographic variation. The surface of the forests consists of deep alluvial deposits, for being washed down over the centuries by the Brahmaputra and other rivers like the Manas and Subansiri. Therefore, vegetation in these forests is greatly influenced by the rich alluvial soils and the monsoon rains. However, most of the original semi-evergreen forests in this eco-region have been converted to grasslands by centuries of fire and other human influences.
The Brahmaputra Valley semi-evergreen rain forests in India houses several varieties of tree species and the typical evergreen tree species found in these forests include the Syzygium, Cinnamomum, Artocarpus, and Magnoliacea. Apart from that, the common deciduous species include Terminalia myriocarpa, Terminalia citrina, Terminalia tomentosa, Tetrameles spp., and Stereospermum spp. Shorea robusta. The canopy trees in these forests are typically 20-30 meters high. The understory of the forests contain the species like Lauraceae, Anonaceae, Meliaceae, Mesua ferrea, Tetrameles spp., Stereospermum spp.. Apart from that, the species like Meliaceae, Anacardiaceae, Myristicaceae, Lauraceae, and Magnoliaceae and several bamboos like Bambusa arundinaria, Dendrocalamus hamilitonii, and Melocanna bambusoides, are also found in the forests.
Apart from harbouring the India's largest elephant population and the world's largest population of the greater one-horned rhinoceros, the Brahmaputra Valley semi-evergreen rain forests in India also houses several other animal species. These species include the Tigers, and Wild Water Buffalo. The forests also overlap with a high-priority (Level I) TCU that extends north to include the subtropical and temperate forests of the Himalayan mid-hills. The well known mammal fauns found in the forests include the families like Cercopithecidae and Bovidae. There are a total of 122 mammal fauna species, including 2 near-endemic species found in these forests. Out of these, the pygmy hog and the hispid hare are confined to the grassland habitats.
The Brahmaputra Valley semi-evergreen rain forests in India are also home to several threatened mammal species including the swamp deer, gaur, clouded leopard, hispid hare, pygmy hog, capped leaf monkey, Asiatic black bear, and sloth bear. The bird fauna in the forests is also quite rich with more than 370 species included in its habitant list. The 2 species that are near endemic among them include the families like Phasianidae and Timaliidae. The forests also overlap with BirdLife International's EBA, and Assam Plains that contains three restricted-range bird species. The Bengal florican is one of the most endangered species found in the forests and is largely limited to the protected areas.