Elevation Effects on Carbon Stock and Tree Species Diversity in Central Himalayan Community Forests, Nepal

Abstract

Forest biomass and carbon management are central to climate change mitigation, particularly in countries where community forestry plays a major role. In Nepal, community forests cover more than 2.4 million ha and are increasingly linked to REDD+ initiatives, making it important to understand how carbon stocks and biodiversity vary across environmental gradients. This study assesses patterns of aboveground biomass, carbon stock, and tree species diversity along an elevational gradient (245–3,549 m a.s.l.) in the Charnawati and Kayarkhola watersheds of Nepal’s central Himalayas. Data from permanent sample plots established in community forests were used to estimate tree biomass, carbon stocks, and species importance value index (IVI). The results indicate strong altitudinal variation in forest structure and composition. Aboveground biomass was highest at lower elevations (500–1,000 m a.s.l.), reaching 344.97 t ha⁻¹, whereas tree density peaked at mid-elevations (2,000–3,000 m a.s.l.) with up to 1,600 individuals ha⁻¹. Species dominance shifted from Shorea robusta at lower elevations to mixed Quercus–Rhododendron forests at mid-elevations and conifer-dominated stands at higher elevations. Regression analyses revealed elevation-specific relationships, with altitude positively influencing carbon stocks at low (<500 m a.s.l.) and high (2,000–3,000 m a.s.l.) elevations, while tree height showed a positive association with carbon stocks only at 1,000–2,000 m a.s.l. However, all models exhibited low explanatory power (R² < 0.11), indicating the influence of multiple interacting factors. Overall, the findings suggest that carbon–biodiversity relationships in community forests are not uniform but are mediated by elevation-specific ecological conditions. These insights highlight the need for elevation-sensitive REDD+ and forest management strategies to enhance both climate mitigation and biodiversity co-benefits.