Temporal changes in tree community structure and carbon stocks in a human-impacted tropical dry evergreen forest, South India

Long-term studies in forest ecosystems are crucial to interpret the dynamics and are essential for conservation and management. However, characterizing long-term dynamics in relation to disturbance across dry tropics is often constrained by a dearth of data particularly from Indian tropics. In this context, a one-hectare permanent plot established in 2001 was revisited in 2011 and further re-censused in 2020 to ascertain species composition, stand structure and carbon stock dynamics of tree community over a 19-year period (2001-2020). Although species richness remained more or less unaffected, tree species composition did vary with the addition and loss of five and 10 species over this period. Species-level mortality rates overshadow the annual recruitment rate resulting in a net decrease in structural components. The results revealed that tree density decreased profoundly to 583 individuals ha-1 in 2020, roughly 46% of the initial inventory. Similarly, basal area is reduced by 40% (from 58.27 m2 ha-1 to 34.91 m2 ha-1), highlighting the impact of increased site disturbance over 19 years. The distribution of individuals and basal area to various diameter classes displayed a reverse J-shaped trend in both the inventories suggesting that all the size classes suffered equally over the years. The total carbon stock was as high as 416.01 Mg ha-1 in the initial inventory and reduced to 250.70 Mg ha-1 in the present re-census. Relative carbon stock calculations revealed that Ficus benghalensis (-46.05 Mg ha-1), Drypetes sepiaria (-22.68 Mg ha-1) and Pterospermum canescens (-14.98 Mg ha-1) represented 64.84% of total carbon stock loss over the period. Among the 29 resourceful species, Memecylon umbellatum, Drypetes sepiaria and Glycosmis mauritiana represented the highly targeted species with varied dietary and medicinal importance. These findings attest the impact of anthropogenic disturbances on species composition and carbon stock potential of the present site, which underline the need for such long-term monitoring efforts useful to forest management and conservation.