Impact of Canopy Openness on Forest Regeneration and Forest Soil Nutrients

Canopy structure plays a critical role in regulating forest regeneration and soil nutrient dynamics, yet its specific effects remain insufficiently understood in the subtropical forests of Nepal. This study investigates the impact of canopy openness on forest regeneration and soil nutrients in six Shorea robusta-dominated mixed community forests within the Chure region of Makawanpur District, Nepal. A total of 90 sample plots for regeneration assessment and 45 soil samples were systematically distributed across three canopy classes-dense (70%-100%), moderate (40%-70%), and open (10%-40%) to evaluate seedling and sapling density, species diversity, and key soil nutrients (N, P, K, SOM, and SOC). The results revealed a distinct trade-off between regeneration density and species diversity. Seedling density was significantly higher in open canopies, following a clear gradient (open > moderate > dense, p < 0.001), whereas sapling density showed no significant difference among canopy classes. In contrast, biodiversity indices (Shannon-Wiener, Simpson's, and equitability) were consistently highest in dense canopies for both seedlings and saplings. Canopy openness also had a strong influence on soil fertility: soil organic matter (SOM), soil organic carbon (SOC), and total nitrogen (N) were all significantly higher in open canopies, supported by positive Spearman correlations (e.g., SOM, ρ = 0.51). Phosphorus (P) and potassium (K) levels were unaffected. These findings highlight a trade-off between regeneration density and diversity, emphasizing the importance of balanced canopy management to sustain both species diversity and soil fertility. The study provides valuable ecological insights for optimizing canopy interventions and promoting sustainable forest management in Nepal's community forests.