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

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.

The Ministry of Science and Innovation of Spain funded this research through the projects UMBRACLIM (PID2019-111781RB-100), VULNIFOR (PID2022-142108OB-I00), and the predoctoral grant PRE2020-094807. Ana Lucia Mendez-Cartin benefited from the Marie Skodowska-Curie Research and Innovation Staff Exchange (RISE)\u2014grant agreement Nr: 101007950. Aitor Ameztegui is supported by a Serra-H\u00FAnter fellowship. The authors are grateful to Gil Torn\u00E9 for his support in fieldwork and to the personnel of the Sant Lloren\u00E7 del Munt National Park for all their help during our fieldwork. We are also grateful to everyone in the USFS in Corvallis, who helped achieve Ana Lucia\u2019s internship\u2014crucial to this paper\u2014with special thanks to David Bell, who hosted and assisted Ana Lucia while she was in Corvallis. We also like to thank Dustin Gannon for all his aid in statistics.