Climatic niche position determines post-fire resilience in Mediterranean forests

Abstract

Fires are a common and significant disturbance in Mediterranean forest ecosystems with a prominent role in their dynamics. The increased frequency, intensity, and extent of fires due to climate change are, however, expected to exceed forests resilience capacity. It is still unknown how resilience capacity changes across species’ biogeographical ranges in relation to pre- and post-fire environmental variability. We analyzed the resilience of Mediterranean pinewoods (Pinus halepensis and P. nigra) to fire in the Eastern Iberian Peninsula and considered the influence of pre- and post-fire climate conditions typified through the species’ climate niche. To assess forest resilience, we applied the Ecological Dynamic Regime (EDR) framework, a methodological approach to quantify the deviation of disturbed trajectories from their dynamic regimes using three indices: amplitude, recovery, and net change. Then, we evaluated how fire characteristics (severity), site attributes (exposure, rockiness), and deviations in the distance to the niche core and edge of the burned populations (centrality-marginality gradient) modulate their resilience to fire. Over 50% of the burned plots exhibited large net change from their dynamic regimes in the mid-term, denoting poor resilience regardless of the species regenerative strategy, and transitioned to shrublands or a different forest type after the fire. Recovery and net change exhibited differences between the two studied species: forests dominated by P. halepensis were overall more resilient to fire across the study range, especially in moist sites, while burned P. nigra forests showed poor recovery and large net changes after fire. For both species, forests location within the climatic niche before and after fire significantly explained post-fire resilience. In general, forests near their climatic niche core showed higher resilience compared to those close to the dry edge of the niche. Synthesis: Our study reveals that post-fire forest resilience depends not only on fire severity and fire characteristics but also on the climatic niche position of the forests. As climate warms and the frequency and intensity of fires increase, forest species will be pushed towards the dry edge of their climatic niches, likely increasing their vulnerability.