Understanding Shorea robusta Gaertn. regeneration challenges in Nepal: A cross-sectoral assessment

Abstract Shorea robusta (Sal) is a keystone species essential for maintaining ecological balance in the tropical forest ecosystem of Nepal. The present study has focused on the regeneration of Sal in both vertical (elevational gradient) and horizontal (regional) spatial patterns in nine community forests across eastern, central, and western Nepal. Using a stratified random sampling method, we studied a total of 810 plots for trees (58,040.6 m²), saplings (7635.60 m²), and seedlings (848.3 m²). Simultaneously, soil samples were collected from 90 plots (0-30 cm depth) from each region across all elevational ranges and analyzed for organic matter, nitrogen, phosphorus, potassium, litter depth, bulk density, soil texture, pH, and moisture content using standard laboratory procedures. Results revealed a significant elevational and regional variability. Forests of the central region showed the highest regeneration capacity compared to the eastern and western regions. The elevational variations also influenced regeneration, with Tarai forests generally recording the higher seedling densities (60,541 plha⁻¹). However, the present study highlighted the major concern of poor regeneration for saplings across all the forests. Soil nutrient analysis reported the variability of organic matter, nitrogen, phosphorus, and potassium levels across the regions influencing regeneration patterns. Principal component analysis (PCA) highlighted the importance of environmental gradients, with elevation and soil nutrients significantly influencing regeneration dynamics. This study emphasized the complex relationships between environmental conditions and forest regeneration and offered insightful knowledge for the community forest user groups to conserve the forest.