Pre- and post-wildfire erosion dynamics as derived from sediment core analyses in Mediterranean ecosystems (Var, Southern France)

Climate change is increasing the frequency and intensity of wildfires in Mediterranean ecosystems. Although these ecosystems are ecologically adapted to fire, they remain ecologically vulnerable, prone to an increased frequency and intensity of wildfires. Wildfires can enhance sediment connectivity within watersheds and disrupt essential processes such as biogeochemical cycling. However, long-term post-fire erosion and ecosystem recovery trajectories remain poorly understood, particularly at the watershed scale. In this study, we reconstruct soil erosion rates (t·ha −1 ·yr −1 ) before and after historical wildfire events in three Mediterranean watersheds in southern France using sediment archives dated with fallout radionuclides. The reservoirs, which drain these watersheds, were created in 1977. While they share similar geo-pedological settings, they differ in terms of size, topography, vegetation cover and fire history. Our results reveal complex interactions between wildfire and erosion dynamics that are specific to each site. Twenty years after the 2003 wildfire, erosion rates remained higher than pre-fire levels, with an increase of +16.7% in PEG02 and +5.7% in PEG07. By contrast, erosion rates in PEG11, which was mainly affected by the 1987 fire, showed a slight decrease forty years later (−4.4%) compared to initial conditions, suggesting a gradual return to pre-fire conditions. These results challenge the assumption that Mediterranean ecosystems fully recover from wildfire-induced erosion within a decade. This study highlights the high scientific value of sediment archives for reconstructing longterm post-fire erosion, offering new insights into the vulnerability and resilience of Mediterranean landscapes in terms of erosion response. • Pre- and post-fire erosion was reconstructed from dated sediment cores. • Low resilience of Mediterranean ecosystems • No return to pre-fire erosion rates, even after >20 years • Post-wildfire erosion rates less than 3 t·ha −1 ·yr −1 . • Manganese is a reliable geochemical tracer of wildfires in Mediterranean ecosystems.