Natural regeneration dynamics and diversity in Pinus sylvestris stands: recommendations for mediterranean forest management

In Serra da Nogueira (northern Portugal), a Natura 2000 site characterized by extensive Quercus pyrenaica forests, even-aged stands of Pinus sylvestris (62–68 years old), originally established for timber, currently lacks silvicultural strategies aligned with biodiversity, regeneration and resilience goals. This study analyzed natural regeneration, and species diversity at the plot scale in two even-aged P. sylvestris stands with contrasting regeneration status and structural conditions, under closed canopy and gap environments. We quantified seedling and sapling abundance by species and analyzed their response to stand structural and environmental variables, including basal area, canopy and shrub cover, LAI, phytovolume, and distance to seed sources. Diversity indices from the Hill series, principal component and redundancy analyses, and species response modeling using generalized additive and linear models were applied to identify key relationships. P. sylvestris seedling recruitment showed considerable variability and limited explanatory power in relation to stand basal area, preventing firm conclusions about optimal conditions. In contrast, Q. pyrenaica regeneration was abundant under basal areas ≈ 30–35 m²ha⁻¹, based on a well-supported model. No clear relationship with basal area was found for Castanea sativa, but seedling abundance decreased with increasing distance to seed sources. Small canopy openings supported P. sylvestris regeneration and native broadleaf enrichment. These findings reflect species-specific responses to stand structure and dispersal constraints. Managing shrub cover and adjusting basal area emerge as key strategies to promote structurally complex, biodiverse stands through incorporation of native broadleaf species. This provides practical guidance to support biodiverse-oriented management in Mediterranean P. sylvestris stands.