What drives the regeneration dynamics in Central Himalayan Mountain Forests of Nepal?

Although forest regeneration has been studied in Nepal’s mountain regions, most research has emphasized single factors such as elevation or canopy cover, with few studies evaluating multiple drivers together. Stage-wise transitions and associated shifts in composition and diversity also remain understudied, particularly in protected areas under passive management. Regeneration dynamics in the Sikles region of the Annapurna Conservation Area were modelled using linear, quadratic, and generalized additive models (GAMs). Principal component analysis (PCA) simplified five soil variables into two composite gradients. Single predictor GAMs examined independent effects of topography, stand structure, and soils, while multivariate GAMs tested their combined influence. Results showed a clear shift in composition and reduced richness from seedlings to saplings, indicating demographic constraints, though evidence for bottlenecks was mixed. Cold-adapted taxa such as Rhododendron spp. dominated saplings at higher elevations. Seedling density was highest at 1500–2000 m (mean = 10,250 ha⁻¹), while sapling density peaked at 3500–4000 m (median = 6,000 ha⁻¹). Diversity indices followed unimodal trends with elevation, with the strongest single predictor GAM fit for seedling richness (adj. R² = 0.41; p < 0.001). Single-predictor GAMs highlighted stage-specific drivers: seedling density was strongly elevation dependent, while sapling density declined with canopy cover and tree density, and soil fertility (PC2) promoted seedling establishment at lower elevations. Multivariate GAMs revealed stronger combined effects, with seedling density shaped jointly by elevation and soil fertility (adj. R² = 0.62) and sapling density constrained by canopy structure and soil fertility (adj. R² = 0.58). These findings show that while single-predictor models identify individual signals, multivariate approaches capture interacting drivers. Conservation strategies should therefore integrate soil management at lower elevations, canopy moderation at mid- to high elevations, and stage-specific monitoring to sustain regeneration under climate change.