Unraveling Elevation-Driven Variations in Forest Structure and Composition in Western Nepal

Understanding how elevation influences forest structure and species composition is crucial for effective conservation in mountainous regions like Nepal, where ecosystems change dramatically over short distances. This study assessed forest dynamics along an elevational gradient (600–3200 m) in Nepal’s mid-hills, incorporating elevational zonation (Tropical, Subtropical, Lower Temperate, and Upper Temperate) and aspect-driven variations. We established 27 square plots (20 × 20 m) at 100 m elevation intervals along a trekking route from Tallo Dungeshwor near the Karnali River to Mahabu Lek, recording all tree species with a diameter at breast height (DBH) ≥ 5 cm. Tree density across the elevational gradient ranged from 250 to 800 trees/ha. Basal area varied between 7.46 and 82.43 m2/ha, while mean tree height ranged from 6.89 to 16.62 m. Species diversity was assessed using the Shannon diversity index, and species dominance was evaluated through the Importance Value Index (IVI). Diversity peaked at mid-elevations, with Shorea robusta and Quercus semicarpifolia identified as dominant species. While minor variations occurred across topographic aspects, statistical analysis confirmed elevation as the dominant driver of forest structure and composition. Correlation analysis revealed a significant positive relationship between elevation and Simpson’s diversity index (r = 0.45, p < 0.05), indicating increased dominance diversity at higher elevations. These findings highlight the critical role of elevation and aspect in shaping forest ecosystems and offer valuable baseline data for climate-resilient management. We recommend conservation planning that is sensitive to topographic gradients, integrates long-term, climate-adaptive monitoring, and engages local communities to anticipate ecological shifts and address mounting anthropogenic pressures in vulnerable montane zones.