Post-fire Recovery of Pinus Halepensis, P. Pinaster, and P. Brutia Forests: Identifying Key Drivers from a Biophysical Approach

Serotiny is the delayed seed dispersal from cones or fruits, which often occurs after heating conferring some species an adaptative advantage under frequent crown fire regimes. In the Mediterranean Basin, the forests dominated by the only three native serotinous pines Pinus pinaster Ait., P. halepensis Mill., and P. brutia Ten. are major contributors to the forest burned area. Here we characterize the post-fire recovery of these three native forests, and we study the influence of burn severity, pre-fire vegetation, and topographic variables on that, using a biophysical remote sensing approach. To achieve these goals, we selected nine study sites (three per pine species) across the Mediterranean Basin. The pre-burn vegetation status and the post-fire recovery four years after the fires were quantified through biophysical variables (fraction of vegetation cover: FCOV, and leaf area index: LAI) obtained from Sentinel-2 imagery. The same satellite was used to calculate the difference of the Normalized Burn Ratio (dNBR), which is a commonly used burn severity index. The topographical variables slope, aspect, and elevation were computed from a digital elevation model. Results showed a similar behavior of the FCOV and LAI. In this sense, we found that none of the six studied forests recovered the pre-fire biophysical status four years after the fires. The recovery of biophysical properties was negatively affected by burn severity, particularly when the pre-fire FCOV and LAI were low. Likewise, the pine forests showed a variable influence of biophysical and topographic variables on post-fire recovery depending on the dominant species, P. brutia forests recovering better the pre-burn biophysical situation in north faces, whereas P. halepensis recovered better when the pre-burn values of FCOV and LAI were high. Our study clarifies the influence of critical variables on forest recovery of three relevant ecosystems, helping forest managers to anticipate critical areas for implementing post-fire restoration actions. This is crucial to preserve the forests in the Mediterranean Basin, which has a high potential erosion risk and is a climate change hotspot.