Assessment of soil erosion rates, carbon stocks, and erosion-induced carbon loss in dominant forest types of the Himalayan region using fallout-137Cs

Forest plays a crucial role in mitigating soil erosion and preserving organic carbon, especially in mountainous regions of Himalayas. However, limited information exists on soil erosion rate, soil organic carbon stock (SOCS), and associated carbon loss in these areas because of the rugged terrain, which poses challenges for reliable estimation using both traditional and modelling approaches. This study used Fallout Radionuclide-¹³⁷Cs to assess soil erosion and carbon loss across various forest types. Results showed that mixed forests had the lowest erosion rates, while degraded forests had the highest, following the order of mixed forest < oak (Quercus) < Rhododendron < deodar (Cedrus) < pine (Pinus) < apple (Malus) < degraded forests. Forests with dense canopy and understory cover experiences reduced erosion (5.9 ± 3.6 t ha^-1 year^-1) while degraded forests showed high soil erosion rates (15.5 ± 6.4 t ha^-1 year^-1) with corresponding carbon displacement of 0.75 ± 0.48 and 1.42 ± 0.71 t ha^-1 year^-1 and carbon emission of 0.23 ± 0.14 and 0.43 ± 0.21 t ha^-1 year^-1 respectively. SOCS (0-15 cm) was inversely correlated with erosion rates, being highest in mixed forests (73.7 ± 32.2 t ha^-1) and lowest in apple orchard (23.41 ± 4.3 t ha^-1) and degraded forests (46.3 ± 19.9 t ha^-1). These findings underscore the need to maintain forest diversity and canopy cover to arrest soil erosion, enhance carbon sequestration, and to improve ecosystem resilience. Conservation and restoration in degraded areas are essential for climate change mitigation and environmental stability in the mountainous landscapes of Himalayas.