Dynamics of aboveground vegetation biomass and carbon stocks along the altitudinal gradients and overstorey composition types in the temperate Himalayan region

Forests, covering approximately thirty percent of the Earth's total surface area, are the world's largest carbon sink and a crucial player in mitigating climate change through carbon sequestration. However, human activities, both developmental and anthropogenic, have resulted in forest degradation, resulting in biodiversity loss, and increased carbon dioxide concentrations in the temperate Himalayan region, where reliable estimates of above-ground biomass and its variation across the landscape are currently lacking. The present study aims to assess aboveground biomass and carbon stocks along altitudinal gradients and overstorey types in the temperate Himalayan region. Across all altitudinal gradients and dominant overstorey composition types, total, tree, shrub, herb, and bryophytes biomass and carbon stocks on average were 372.7, 369.1, 2.76, 0.77 and 0.10 Mg ha−1, and 177.1, 175.3, 1.31, 0.37 and 0.05 Mg ha−1, respectively. The biomass and carbon stock of total and individual vegetation components differed significantly along the altitudinal gradients and overstorey composition types. Total and tree aboveground biomass and carbon stocks showed a consistent gradual increase along altitudinal gradients, peaking at middle elevations and declining thereafter at higher altitudes. The result highlighted the variation in biomass and carbon stocks in the temperate Himalayan region is influenced by factors such as the presence of individuals in large-diameter classes, higher stem densities with increased basal area, and forest management practices along altitudinal gradients. The study also emphasized the role of dominant overstorey composition types in biomass and carbon stock distribution in the temperate Himalayan region. However, tree, shrub, herb, and bryophyte biomass production responded differently for dominant composition types. Shrub and herb biomass along with their carbon stocks appeared to be positively associated with higher resource availability under deciduous broadleaf overstorey types, while the trees and bryophytes biomass and carbon stocks were found to be higher under coniferous stands. Mixedwood stands, on the other hand, were found to be intermediate between the pure stands, but had higher biomass and carbon stocks at higher altitudes. Therefore management interventions should aim at maintaining a diverse range of overstorey composition types for promoting the ecosystem functions and services of temperate Himalayan forest ecosystems.