Topographical heterogeneity governs species distribution and regeneration potential by mediating soil attributes in Western Himalayan forests

Abstract The present study is an attempt to understand variation in species composition and diversity and soil properties along topographic gradients in Western Himalayan reserve forests (400-3000m asl). To analyze changes in floristic composition, diversity, and regeneration status, we measured woody vegetation in forest plots at different altitudinal levels and contrasting aspects (North and south). Trees (diameter at breast height (DBH) > 10cm) and saplings (3-10cm DBH) were sampled in 10m×10m plots, shrubs were sampled in 5m×5m plots and seedlings (0-3cm DBH) were sampled in 1m×1m plots. To study variation in soil properties, samples were collected from each forest stand in five replicates from layers of 0-10cm, 10-20cm, and 20-30cm in soil depths. Canonical Correspondence Analysis (CCA) was applied to identify important factors that govern species distribution. Variance partitioning was conducted to quantify the relative contribution of elevation, slope aspect, vegetation attributes, and soil properties on regeneration potential of tree species. We found that environmental filtering shapes local species composition and associated edaphic factors in the region. Species richness and diversity were found to decrease with elevation. Soil properties (Organic Carbon, pH, and texture) and associated vegetation parameters did not vary significantly between the aspects. CCA confirmed that species composition was positively related to moisture content and available phosphorous at higher elevations, while reduced weathering rates and bulk density at lower elevations might have caused relatively lower nutrient turnover rates. Our study concludes that topographical variation and increased sum of soil nutrients are highly favorable for growth and development of plant species.