North-east India, represents the confluence zone between the Indian, Indo-Malayan and Indo-Chinese biogeographical regions. The North-east zone is therefore the "biogeographical gateway" for much of India's fauna and flora, and as a consequence, one of the richest in biological values. The state of Assam is the largest part of zone- 8 representing the North-east India (Rodgers & Panwar, 1988). Of all zones of India, it is perhaps the richest in communities, in species and in endemism.

The variety of flood plains of Brahmaputra river and the forested hills with a mixture of swampy grasslands, evergreen, deciduous and sub-tropical forests are floristically extremely rich and also contain significant primate, carnivore and bird communities. The herbivore fauna of the swamp grassland communities is represented by elephant, rhinoceros, buffalo, swamp deer, hog deer, pigmy hog, and hispid hare. North-east India contains 10 of the 15 known species of primates (Choudhury, 1989). Some of the very rare primates like pig tailed and stump tailed macaque, phayrey's leaf monkey, golden langur and hollock gibbons are characteristic of the forested area of this zones. The state also offer a home to a wide variety of birds particularly the pheasants and the hornbills.

It has been observed in the recent years, that the basic ecological format of the state is changing due to multifaceted impacts of various developmental projects that are essential parts of modernization and industrialization in the state (Bhattacharjee, 1996). The number of forest based industries in the state of Assam is fairly significant. There are about 52 plywood mills, 552 saw mills, 1 match factory, 3 match splint unit, 2 paper mills, currently operating. River valley projects have also exerted tremendous pressure on the natural habitat of Assam. The projects like Borapani Hydro Electric Power (HEP), Dhansari Hydel scheme and Puthjmari projects are some of the proposed projects that are likely to result in the decimation of areas under wildlife habitats. Taking forest cover alone as a simple index of habitat loss, one can predict the adverse effect of this loss, on animal population. According to the assessment of the forest cover of the country on a two year cycle conducted by Forest Survey of India, the forest cover of the north eastern states are declining at the rate of 0.5 percent which is much higher than the national average (0.2 percent) per two years.

In such a precarious situation, it becomes all the more crucial to make a careful assessment of the possible implications of all the developments, whether big or small in different sectors. Environmental Impact Assessment of any proposed developmental project not only provides an adequate understanding of the likely environmental impacts but also provides the scientific basis for evolving mitigatory strategies and environmental safeguards wherever possible.