Tree Diversity and Population Structure of a Protected Lowland Tropical Forest in Barail Hill Range, Northeast India

Tree species diversity and population structure of a lowland tropical forest in Barail Wildlife Sanctuary, Assam falling under the important Barail Hill Range of Northeast India was carried out during 2012-2015. 42 quadrat (20m x 25m) were laid in three forest stands selected on the basis of location and species dominance in the lowland forests of the sanctuary following random sampling method. The vegetation data collected were analyzed for density, frequency, basal area, and the Importance Value Index (IVI). Familial importance value was also worked out. Tree Species diversity was calculated following Shannon diversity index and Concentration of Dominance was calculated by Simpson’s Index. Population structure was worked out based on the girth of individual trees belonging to different species. A total of 109 tree species (≥ 30 cm gbh), belonging to 45 families were rerecorded from the sanctuary. Tree species richness was recorded highest for stand I that comprised 88 tree species, followed by stand III (69 tree species) and stand II (48 tree species). Meliaceae, Sapindaceae and Sterculaiceae were the dominant families in different stands. Shannon diversity index was found highest in stand I (4.01) followed by stand III (3.87) and stand II (3.61). The dominant species in stand I were Canarium strictum (IVI 17.58) While in stand II, it was Maniltoa polyandra (IVI 22.31) and Elaeocarpus macrocerus (IVI 19.84) in stand III. The population structure of all the three stands showed a reverse J-shaped curve where as in case of the dominant tree species, individuals in different stands were unequally distributed. The lowland forests of Barail Wildlife Sanctuary are a repository of huge biodiversity in the very important Barail Hill Range landscape of Northeast India that falls under the Indo-Burma Hotspot of biodiversity. Being the only protected area in the entire South Assam region, it acts as an important refuge for the native plants and animals, including the rare, endangered and threatened species of the region. The study would contribute a great deal towards the understanding of tree species composition, diversity, species coexistence and population structure of this very important wildlife sanctuary which will pave the way for its better management and conservation. Key Words: Species Diversity, Richness, Structure, Lowland Tropical Forest, Barail Wildlife Sanctuary