Woody biomass-carbon and soil organic carbon stock in subtropical forests of Garhwal Himalaya

The present study was undertaken in ten important subtropical forests growing in foothills of Garhwal Himalaya to estimate the biomass and carbon in different tree components and variations in Soil Organic Carbon (hereinafter SOC) stocks. The sample plots were laid out using two ways stratified random sampling approach and the biomass was evaluated by applying linear regression equations. The soil samples were collected at three different depths viz., 0–10 cm, 11–30 cm and 31–60 cm to analyse the pH, bulk density and SOC stock. The tree density and TBC values significantly varied in different forest types and ranged from 300 ± 11.55 to 840 ± 15.55 trees ha⁻¹ and 12.55 ± 4.62 to 36.23 ± 5.77 m² ha⁻¹, respectively. The total biomass density values were recorded between 185.59 ± 1.23 Mg ha⁻¹ and 1572.1 ± 4.27 Mg ha⁻¹, whereas carbon stock values ranged from 82.64 ± 0.82 Mg C ha⁻¹ to 700.06 ± 2.85 Mg C ha⁻¹. The soil was acidic to alkaline in nature (indicated by the pH). The SOC stocks were significantly varied (F = 9.872, P < 0.001) at various depths and altitudes reflecting values between 28.05 ± 5.66 Mg C ha⁻¹ to 98.89 ± 27.31 Mg C ha⁻¹. The diameter class distribution patterns of most of the forests have indicated a positive skewed curve, but considerable biomass was observed in higher dbh classes. Our results have indicated that the tree biomass depends more on the size class (Adj. R² = 0.3475; F = 133.5991; P < 0.0001) instead of the structure metrics i.e., stand density (Adj. R² = 0.3036; P = 0.0573) and diversity (Adj. R² = 0.1232; P = 0.9136). This has revealed that the girth of species was the deciding factor to determine the biomass and carbon storage, not the density and diversity. High CO₂e values have indicated that the woody vegetation has immense capacity to regulate the carbon. Therefore, the role of uneven aged vegetation in accumulation of biomass and carbon in foothill regions of Garhwal Himalaya is noteworthy.