Influence of functional diversity on aboveground biomass accumulation in subtropical sub montane forests

Subtropical evergreen sub-montane forests in Punjab, Pakistan, are vital for carbon sequestration and play an essential role in supporting local communities. While the global importance of tree species diversity in enhancing aboveground carbon (AGC) storage is well established, there remains limited empirical evidence from Pakistan's forest ecosystems. This study investigated how taxonomic and functional diversity, alongside topographical variables, influence AGC across four districts in Punjab. Taxonomic metrics such as the Importance Value Index (IVI) and genus richness were computed, along with functional diversity indices including functional richness (FRic), functional dispersion (FDis), functional divergence (FDiv), and functional evenness (FEve). AGC was estimated using species-specific allometric equations, and linear mixed-effects models were applied to identify the most influential predictors. Acacia modesta and A. nilotica emerged as the dominant species in the studied sites. While species richness and biomass increased with elevation, Shannon diversity showed a negative relationship with elevation. AGC values ranged from 100 to 350 Mg ha^-1 across the study sites. Among diversity metrics, FRic (0.042) and FDis (0.342) were significantly associated with higher AGC, whereas taxonomic diversity measures showed weaker correlations. Although elevation was a strong predictor of diversity patterns, it did not have a significant direct effect on carbon storage. These findings underscore the importance of incorporating functional trait diversity and topographic variability into forest management strategies to enhance carbon sequestration, strengthen ecosystem resilience and support sustainable rural livelihoods.