Forest dynamics after drought-induced mortality: a global assessment

Forest mortality related to extreme drought has been reported worldwide, affecting all biomes and plant types (angiosperm vs. gymnosperms, evergreen vs. deciduous). The forecasted increased frequency and intensity of drought events as a consequence of anthropogenic climate change could promote an increasingly widespread drought-induced mortality in the future. However, little understanding exists on ecological trajectories or the replacement processes after drought-induced mortality events. We assess (through a collaborative initiative) the extent of short-term self-replacement patterns in temperate forest ecosystems worldwide (N = 131 sites) in relation to: species traits, the major bioclimatic characteristics of reporting sites, and past management and disturbance legacies in the affected sites. We found that alternate species replaced pre-drought dominant tree species in ~70% of the examined cases, whereas in ~10% of the study sites there was no replacement by woody vegetation. Replacement was influenced by management intensity, and post-drought shrub dominance was higher when pathogens acted as co-drivers of tree mortality. No significant replacement patterns were found in relation to the bioclimatic characteristics of the reporting sites (environmental location) or of the dominant species (bioclimatic ‘niche’). Shifts to both more xeric and to moister communities were observed. These changes were driven by species with higher limits of tolerance to dry conditions and by species with wider bioclimatic ranges, respectively. Overall, our findings highlight the potential for major forest ecosystem reorganization in the coming decades.