Impact of altitudinal gradients on composition, biomass and soil nutrients of Cedrus deodara forests in the Northwestern Himalaya

Himalayan forest ecosystems provide a wide range of ecological services, including climate regulation, water purification, biodiversity conservation and the production of forest goods. These ecosystems are critical for maintaining ecological balance and human well-being. Sustaining these functions requires healthy floristic composition, high biological productivity and balanced nutrient cycling. This study evaluates the vegetation structure, biomass, carbon stock and soil nutrient status of moist temperate Cedrus deodara forests across three altitudinal gradients (1600–1900 m, 1900–2200 m and >2200 m) and three forest ranges (Bhajji, Mashobra and Koti) within the Shimla Forest Division. A total of 38 plant species were recorded, including 7 tree species, 11 shrubs and 20 herbaceous species. Key ecological parameters such as density, basal area, Importance Value Index (IVI) and diversity indices were assessed. Tree density ranged from 553.33 to 786.67 individuals ha⁻¹ and basal area varied from 52.52 to 121.05 m² ha⁻¹. Tree and shrub densities declined with increasing altitude, while herb density exhibited no consistent trend. Species richness and Shannon diversity index also declined with elevation. Biomass and carbon stock of Cedrus deodara followed a hump-shaped pattern, peaking at mid-altitudes, with total biomass ranging from 458.06 to 835.93 t ha⁻¹ and carbon stock from 219.28 to 382.48 t ha⁻¹. Soil pH and available nitrogen, phosphorus and potassium were highest at lower elevations, while soil organic carbon was greatest at higher altitudes.