Tree community structure, carbon stocks and regeneration status of disturbed lowland tropical rain forests of Assam, India

Tropical rain forests are global hotspots of biodiversity and key climate change regulators. Despite the decades of conservation efforts, tropical forests are increasingly under continuous threat from human activities. Therefore, understanding the impact of anthropogenic disturbances on biodiversity is necessary for better conservation and management. This study focused on a tropical rainforest located in Kakoi reserve, Assam, in the northeastern Himalayas, aiming to compare tree species composition, diversity, carbon stocks, and regenerating status in two forest sites experiencing disturbance regimes. A total of 55 tree species representing 36 genera and 26 families were recorded in the study area. The tree species richness was slightly higher in moderately disturbed (MD) Dirgha than in the highly disturbed (HD) Kakoi-Rajgarh forest. Tree density and basal area were 582 and 446 individuals ha−1, 38.43, and 32.63 m2 ha−1, respectively, in MD-Dirgha and HD-Kakoi-Rajgarh. Forest stand structure followed a typical reverse J-shaped trend in both sites, with a lesser density of large girth-class (>330 cm girth at breast height) individuals in HD-Kakoi-Rajgarh, reflecting the influence of past onsite disturbances. The analysis of the regeneration strata depicted that seedling and sapling density was 1.8 and 1.4 times lower in HD-Kakoi-Rajgarh compared to MD-Dirgha. Above-ground biomass and total carbon stocks were maximum in MD-Dirgha, followed by HD-Kakoi-Rajgarh. About 63.64% of the recorded tree species, including Critically Endangered Vatica lanceifolia are under IUCN Red List Categories, thus stressing the need for conservation. Our findings suggest that conserving species diversity and carbon reserves in tropical forests would principally depend on minimizing forest loss and degradation.