Biophysical drivers of Pinus nigra subsp. salzmannii post-fire regeneration: role of fire refugia

Abstract Context Recent shifts in fire regimes challenge recovery of forest ecosystems. In Catalonia, Spain, the capacity of Pinus nigra to persist has been affected by recent high severity fires. Objectives To understand the biophysical conditions that support P. nigra recovery after high severity fire, we investigate the main biophysical drivers—seed availability, community interactions, water, and nutritional constraints—affecting post-fire regeneration patterns in Catalonia. Methods We identified fire refugia and calculated the distance-weighted refugia density (DWD) across four fire footprints to represent the seed source abundance. We surveyed abundance of regeneration and shrub cover on 270 sites. We tested identical statistical models for “inside” and “outside” fire refugia, to assess the role of fire refugia and main biophysical drivers on post-fire regeneration. Results The DWD had a positive effect on post-fire P. nigra recovery, with a stronger effect outside refugia than inside. Inside fire refugia, canopy trees had a sheltering effect on post-fire regeneration, reducing negative effects of heat load, particularly at higher aridity plots. Presence of Rubus spp. broadleaf shrubs enhanced the abundance of regeneration both inside and outside refugia. Total shrubs cover negatively impacted regeneration inside refugia and sites with greater aridity outside refugia but exerted a facilitative effect on P. nigra regeneration outside of fire refugia at sites with lower heat load. Conclusions Seed source abundance is an integral driver of post-fire regeneration however, biophysical site conditions are important filters that amplify or diminish regeneration. This ecological information can be used to tailor post-fire management goals for forest recovery.