High Dominance of Shorea robusta Gaertn. in Alluvial Plain Kamrup Sal Forest of Assam, N. E. India

The study emphasizes on the community characteristics of naturally regenerated sal forest of Kamrup district, Assam, India. Sal is one of the most important timber yielding plants and also good source of aromatic gum and non- timber forest product. These forests are exposed to over-exploitation, deforestation, encroachment and alteration in land use and land cover and in return being replaced by secondary regenerated sal forest. Altogether, 71 plant species were recorded from the selected sal forest. Herbaceous layer of the forest was most species rich (30 species) layer followed by tree and shrub species. Leguminosae and Asteraceae were among the most dominant families in the forest while large number of families was monospecious. Shorea robusta has contributed about 90% of the total stand density (2559 individual ha-1) of the forest, while species like Erythrina suberosa, Delonix regia and Pterospermum acerifolium were represented by single stem. Similar to that of stand density, sal have contributed to the maximum basal area of the forest. The girth class distribution confirmed a reverse J-shaped distribution, with higher density in lower girth classes and sharp decline thereafter. Total density of shrubs and herbs was recorded 2 individuals m-2 and 63 individuals m-2, respectively. Based on the dominance, Shorea robusta showed highest dominance followed by Zizyphus rugosus. Diversity index for tree, shrub and herb species was recorded 1.43, 2.30 and 3.28, respectively. Dominance index showed reverse trend to that of diversity index. About 84% of the plant species showed contagious distribution, however none of the species exhibited regular distribution. The forest is heterogenous in composition with high dominance of Shorea and is under regenerating stage. Therefore, for sustainability of the forest it requires effective conservation measures for sal and its associate plant species.