Fire refugia recovery trends and patterns in Mediterranean pine forest ecosystems

Climate change, land cover changes, and fuel accumulation are altering the historical fire regimes in Mediterranean fire-prone ecosystems. Disentangling the role of climate and spatial structure on post-fire recovery of fire biological legacies is critical, as these unburned or low-severity areas within fire scars (fire refugia), by containing residual pre-fire vegetation, facilitate post-fire species persistence. Fire refugia were identified within burned patches of six Pinus halepensis Mill. stands in a Natura 2000 Network site, based on the reconstruction of a 40-year (1981-2020) fire chronology. Landsat annual time-series of Normalised Burn Ratio (NBR) were used to assess fire refugia post-fire recovery temporal trends and patterns. Climate parameters (maximum and minimum temperature and precipitation of four seasons, over time) and fire severity mosaic heterogeneity metrics (landscape and class level) were used as predictors to identify drivers of post-fire vegetation condition. Exploratory analyses concerning the distribution, the temporal structure, and the interrelationships among variables indicated that the dataset is characterised by (i) a strong temporal recovery signal in NBR, (ii) non-stationary climate drivers, especially temperature, and (iii) highly variable and skewed precipitation regimes. The multivariate structure and collinearity of climate predictors, assessed by means of principal component and correlation analyses, showed that climate variability is structured around a dominant temperature signal and a secondary precipitation-seasonality gradient. Random Forest regression analysis implemented to assess the relative importance of climate and fuel mosaic heterogeneity metrics in explaining post-fire recovery, through a non-parametric perspective, reinforced and extended the insights obtained from exploratory and multivariate analyses. It revealed that post-fire recovery, as appraised by the NBR, is governed by a combination of strong climatic constraints and landscape-mediated buffering mechanisms. These findings suggest that climate sets the overarching limits to recovery, while fire refugia connectedness modulates their recovery trajectories, thus providing spatially structured sources of resilience. From the perspective of an integrated approach to fire management, silvicultural interventions aimed at increasing forest structure horizontal and vertical heterogeneity, by mitigating fire behaviour, may determine the preconditions for heterogeneous fire mosaics with well-connected fire refugia, likely to enhance forest recovery under future climatic stress.