Patterns of forest community diversity, regeneration potential and carbon storages along an altitudinal gradient in Eastern Himalaya, India

This study showed changing patterns in the plant species composition, diversity, and carbon storage potential of different forests along altitudinal gradients (i.e. 100 - 1900 m) in Eastern Himalayan India. Different tree, shrub and herb species were sampled along the altitudinal gradients ranging from tropical to temperate forests through Nested Plot design. In each forest, vegetation sampling was made by establishing a permanent plot of 250 m x 250 m as per ISRO-GBP/NCP-VCP protocol. Individuals of trees >= 10 cm girth at breast height (GBH), shrubs and herbs were recorded in 4, 8 and 16 subplots of 31.62 m x 31.62 m, 5 m x 5 m and 1 m x 1 m, respectively. Community attributes such as species richness, density, basal area, diversity indices and biomass and carbon storages were computed for each study site. A total of 5 forest communities (2 each from tropical and subtropical and one from temperate forest) were identified. The woody species diversity was highest in the subtropical forest followed by tropical and temperate forest. Altitude played an important role in the Eastern Himalayan Mountains in the establishment and distribution of forest community. Forest community composition changes with elevation, for instance, the dominant communities like Dipterocarpus retusus-Phoebe goalparensis-Schima wallichii (D-PS), Gmelina arborea-Schima wallichii-Duabanga grandiflora (G-S-D), Schima wallichii-Duabanga grandiflora-Alstonia scholaris (S-D-A), Alstonia scholaris-Terminalia myriocarpa-Bischofia javanica (A-T-B) and Acer thomsonii-Rhodendron arboreum-Quercus lamellose (A-R-Q) were present at elevational ranges of 100-300 m, 300-700 m, 700-1100 m, 1100-1500 m and 1500-1900 m, respectively. The study showed that about 41-57% of the tree species exhibited good regeneration followed by 23-30% as fair, 6-16% as poor, and 6-21% species did not show regeneration along the altitudinal gradient. The total biomass carbon (Mg C ha-1) varied from 84.74 to 163.56 in tropical, 103.12 - 156.41 in subtropical and 133.05 in temperate forest. In conclusion, community composition, regeneration pattern and biomass carbon storage changes along altitude because of altered biophysical characteristics. However, despite variations in elevation, factors for forest disturbance at different altitudes significantly contributed to the community attributes and overall accumulation of biomass carbon. Hence, the traditional management practices carried out by local communities also play a crucial role in shaping the structure, composition, and carbon dynamics of forest ecosystems. Understanding the impacts of these practices is essential for promoting sustainable forest management by conserving forests and preserving carbon stocks for mitigating climate change in future. This study emphasizes the importance of long-term forest monitoring to promote biodiversity conservation and formulate conservation strategies that support sustainable forest management policies to which ensure continuous provision of ecosystem services in the region.