Fine-scale environmental filtering and seed limitation shape early post-fire regeneration patterns in Mediterranean Pinus halepensis Mill. forests

Post-fire regeneration in Mediterranean pine forests is increasingly constrained by recurrent high-severity fires and post-disturbance interventions. We assessed the drivers of early natural regeneration in a coastal Pinus halepensis Mill. forest in Spotorno (NW Italy) affected by two recent high-severity wildfires (September 2006 and July 2015) followed by salvage logging. Pine seedlings were mapped in spring 2025 with an RTK GNSS antenna, while high-resolution UAV images and LiDAR products were used to derive terrain- and forest structure-based predictors. Topographically mediated constraints on regeneration were quantified using the Topographic Wetness Index (TWI) and the Heat Load Index (HLI), which capture spatial variation in soil moisture accumulation and heat exposure. Seed availability was represented by the distance to remnant adult pines, identified from the canopy height model using a local-maximum filtering approach. Spatial point pattern analysis (inhomogeneous Ripley’s K and pair correlation) was used to test whether empirically evident regeneration clusters reflected plant–plant interactions, or environmentally-driven density variation. Drivers of regeneration were modelled using GLMs, GAMs and Random Forests (RF), and two pseudo-absence strategies in the RF were explicitly compared by training models with (i) ecologically informed, spatially homogeneous pseudo-absences and (ii) randomly sampled pseudo-absences. The informed pseudo-absence Random Forest achieved substantially higher discrimination (AUC = 0.895; ACC = 0.821; SEN = 0.785; SPE = 0.864) than the random-absence model (AUC = 0.653; ACC = 0.607; SEN = 0.648; SPE = 0.571). The best model was applied to generate a 5 x 5 m ecological suitability map identifying regeneration “hotspots”, i.e., near seed sources under warm, well-drained microsite conditions, and persistent “coldspots” in convergent terrain and seed-limited areas. This workflow provides an operational, transferable basis for precision-oriented post-fire restoration planning in Mediterranean landscapes where passive recovery is uncertain.