Altitudinal gradient and anthropogenic disturbance alter soil quality index and biomass carbon in Banj Oak (Quercus leucotrichophora) forests of Garhwal Himalaya, India.

The forests of Garhwal Himalaya are undergoing escalating anthropogenic pressure, which pose critical threats to their ecological integrity, biodiversity, soil physical and biochemical functioning. Understanding how these disturbances affect biomass carbon and soil health across altitudinal gradients is essential for sustainable management. This study evaluates the impacts of forest disturbance on carbon sequestration, and soil quality in Quercus leucotrichophora dominated forests across an elevation gradient (1600-2600 m asl) in Uttarakhand, India. The sampling was conducted at five elevation ranges i.e 1600-1800, 1800-2000, 2000-2200, 2200-2400, and 2400-2600 m asl using a stratified random sampling method with distinct disturbed and undisturbed sites, and 10 quadrates (10 × 10 m) were laid in each site. Forest disturbance was quantified using field indicators (canopy cover, lopping intensity, cut stumps, grazing trails). Biomass and carbon stocks were estimated using non-destructive allometric equations, following IPCC (2000) guidelines. Soil samples (0-15 cm, 15-30 cm) were analyzed for physicochemical and biological properties including pH, SOC, NPK, bulk density, cation exchange capacity, and dehydrogenase activity. Soil Quality Index (SQI) was computed using both additive (SQIa) and PCA-weighted (SQIw) methods. Disturbed sites exhibited significantly lower total carbon density (TCD) (91.91-295.68 Mg C ha-1) as compared to undisturbed sites with TCD: 152.40-500.29 Mg C ha-1. Soil quality indices declined evidently under anthropogenic disturbance across all elevations. The SQIa was relatively lower in disturbed sites (2.50 at 0-15 cm; 2.26 at 15-30 cm) than in undisturbed forests i.e 2.95 and 2.74 at respective depths, demonstrating a clear decrease in functional capacity of soil. Likewise, when averaged across sites and combined over both soil depths, the SQIw was lower in disturbed forests (2.38) compared to undisturbed sites (2.84). The undisturbed forest sites sustained better soil quality across elevations and depth, whereas disturbed sites showed lower SQI values, pointing towards the degradation of soil ecosystem functioning owing to anthropogenic disturbance. The forest disturbance along elevation gradients lead to measurable degradation in biomass and soil quality. The findings underscore the urgent need for disturbance-mitigating policies and ecological restoration strategies to sustain forest productivity and ecosystem services in the Himalayan region.