Influence of vegetation and soil properties on carbon stocks in Shorea robusta forests under different disturbance regimes

Sal (Shorea robusta) forest ecosystem is among the most carbon-dense terrestrial ecosystems globally, playing a crucial role in climate change mitigation through carbon (C) sequestration in biomass and soil. Disturbances are key factors influencing vegetation diversity and soil nutrient status, which in turn influence biogeochemical cycling and ecosystem functions. To accurately assess the effects of disturbance regimes on carbon stock potential and stability, it is essential to quantify the dynamics of vegetation biomass carbon (VBC) and soil organic carbon (SOC) stocks along with their underlying drivers. However, this information is currently limited, and the mechanisms governing VBC and SOC stock responses to disturbance are poorly understood. Present study investigated the effects of disturbance regimes categorized as no disturbance (ND, <5% tree basal area removal), low disturbance (LD, <20%), moderate disturbance (MD, <50%), and high disturbance (HD, >50%) on carbon stock patterns in sub-tropical deciduous sal forests. It also explored the interdependence between vegetation structure (density, basal area), diversity, and soil properties in influencing VBC and SOC stocks. Greater tree recruitment, vegetation diversity, and soil nutrients were observed under moderate disturbance compared to other regimes. Under-canopy biomass C stocks ranged from ∼46.5 to 182.6 Mg C ha^-1, comprising 13.1-65 %, while SOC stock ranged from ∼4.7 to 54.8 Mg C ha^-1, contributing 27.4-37.3 % to forest C stocks. Variations in stand structure, diversity, and soil properties influenced by disturbance regimes, promoted structural complexity, and improved nutrient availability and C stocks. Predictive model analysis revealed that variations in VBC and SOC stocks were strongly determined by changes in under-canopy diversity and soil properties, especially soil nutrients (N, P) and microbial biomass. Path analysis indicated that mechanisms influencing VBC and SOC stock dynamics following disturbances differed between under-canopy and canopy vegetation. This study highlights the importance of disturbance regimes in shaping vegetation recovery and soil health, providing a foundation for developing effective management strategies to optimize carbon storage in natural forest ecosystems.