Stand structure drives vegetation carbon storage while soil texture regulates soil organic carbon in Nepalese mid-hill community forests

Abstract

Forest carbon stocks in Nepal’s mid-hill community forests are influenced by interacting biotic and abiotic drivers; however, the relative importance of these drivers remains insufficiently understood. Vegetation carbon and soil organic carbon (SOC) were quantified across three forest types: Shorea robusta, Pinus roxburghii, and mixed broadleaved forests, using 19 nested circular plots (500 m2) and stratified soil sampling to a depth of 80 cm. Fourteen predictors representing stand structure, anthropogenic disturbance, soil properties, topography, and climate were evaluated using correlation analysis and principal component analysis (PCA). Shorea robusta forests stored significantly higher vegetation carbon (113.5 ± 7.1 Mg C ha−1) and SOC (102.0 ± 2.3 Mg C ha−1) compared to the other forest types. At the plot scale, basal area and canopy cover were the strongest positive predictors of tree carbon, while anthropogenic disturbance exerted a negative effect (correlation coefficient = − 0.60). SOC was primarily regulated by soil texture, with silt exerting a positive effect and sand a negative one; canopy cover was the only significant structural correlate. PCA confirmed that stand structure and disturbance accounted for most variation in vegetation carbon, whereas soil texture determined SOC patterns. These results indicate that maintaining stand basal area and canopy integrity while minimizing biomass-removal disturbances is essential for optimizing ecosystem carbon storage in community-managed mid-hill forests. This has direct implications for REDD+ implementation and national carbon accounting. Current management practices should incorporate both biotic and abiotic factors influencing carbon stocks.