Elevation-driven influences on soil nutrient dynamics and vegetation structure in temperate subalpine forests of the Western Himalaya

This study examines patterns of soil physico-chemical properties, vegetation attributes, and their interrelationships along an altitudinal gradient (2,100–3,300 m asl) in high-altitude forests of the Western Himalayas. Vegetation was sampled at three locations along 100 m altitudinal intervals within the Kedarnath Wildlife Sanctuary, Uttarakhand. In each altitudinal belt, three plots (50 m × 50 m) were randomly marked; a total of 105 plots were studied. For tree species, within three plots, 10 quadrates of 10 m × 10 m were laid for trees and saplings, 20 quadrates of 5 m × 5 m for shrubs and seedlings, and 40 quadrates of 1 m × 1 m were laid for herbs. Soil samples were collected from five points along the same transects at two depths (0–15 cm and 15–30 cm) and then composited for physicochemical analysis. Results reveal that soil properties exhibited distinct trends with elevation, with soil moisture content, soil porosity, water-holding capacity, sand content, available phosphorus, and total nitrogen generally increasing, while bulk density, silt content, soil organic carbon, soil organic matter, and C:N ratio declined. Significant differences were observed between upper and lower soil depths, with lower depths exhibiting higher moisture, pH, and clay content, whereas upper depths had higher organic carbon, nutrients, and water-holding capacity. Vegetation patterns also varied with altitude; tree density and species richness declined, shrub richness fluctuated without a clear trend, and herb richness increased. Elevational variation in soil and vegetation was driven by climatic constraints and plant-soil interactions. Higher soil moisture, porosity, and water-holding capacity at higher elevations reflect lower temperatures and reduced evapotranspiration, while declining bulk density indicates reduced compaction. Lower soil organic carbon levels suggest reduced litter inputs from declining tree biomass, whereas higher nitrogen and phosphorus levels reflect reduced nutrient losses. Depth-related patterns result from particle translocation and surface organic inputs. Canonical Correspondence Analysis showed that altitude, soil moisture, bulk density, and silt content were the primary drivers of species composition across life forms. Other soil variables also influenced the composition of specific plant groups in the high-altitude forests of the Himalayan region. The study suggested long-term ecological monitoring of forests for a better understanding of the influence of soil dynamics and vegetation composition in the Himalayan region.