Assessing the impact of canopy opening in regeneration status of tropical Terai forest of Nepal

Understanding how canopy structure influences regeneration is crucial for sustainable management of forests, particularly critical tropical forests. Although numerous studies have examined regeneration patterns, few have assessed how both seedling and sapling layers independently respond to different canopy gradients across multiple forest types and developmental stages in unmanaged tropical forests. This study addresses this gap by investigating regeneration dynamics in relation to canopy cover across two tropical forest types. Data was acquired through permanent sample plots established by the Forest Research and Training Centre (FRTC), Nepal using two-phased cluster sampling establishing grid of 4km*4km square grid in the first phase followed by drawing a sub sample of the cluster for field measurement in the second phase. Seedling and sapling densities were analyzed across four canopy cover classes (0–25%, 25–50%, 50–75%, and 75–100%) and three developmental stand stages (Reg-Pole, Small Saw Timber and Large Saw Timber) withing those two forest types; Shorea robusta forest and Other forest based on species dominance. Within S. robusta forest, seedling density tended to be higher under mild to close canopy while sapling density remained relatively uniform across canopy classes. However, Kruskal–Wallis tests indicated that those variations were not statistically significant reflecting the species' broad regeneration tolerance. In contrast, Other Forest type showed significantly higher seedling densities under moderate to high canopy closure as confirmed by Post hoc comparisons. Sapling density, however, remained unaffected by canopy variation in both forest types. Additional analysis across developmental stages revealed that mature forest stands support seedlings while seedlings prefer younger forest stands. The study underscores the importance of forest type, stand maturity and canopy structure sensitive approaches for regeneration management providing new ecological insights into canopy-regeneration interactions in tropical forests and offers practical guidance for silvicultural planning in those forests.