Post-fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response

Forest fires and post-fire practices influence sediment connectivity (SC). In this study, we use the 'aggregated index of connectivity' (AIC) to assess SC in five Mediterranean catchments (198-1090 ha) affected by a wildfire in 2012 in south-eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post-fire management, and 2 years after the fire including all practices (hillslope barriers, check-dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)-derived digital elevation model (DEM, 2 m x 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC(OUT)), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AIC(N-OUT)). The output analysis includes the SC distribution along the catchments and at local scale (929 sub-catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area-specific sediment yield (SSY) at 10 new (built after post-fire practices) concrete check-dams located in the catchments (SSY = 1.94 Mg ha(-1) yr(-1); sigma = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC(N-OUT). The structural SC maps - removing the rainfall erosivity influence - allowed evaluating the actual role played by the post-fire practices that reduced SC (x over bar = - 1.19%; sigma = 0.41); while functional SC was linked to the actual change of SC (x over bar = + 5.32%; sigma = 0.62). Hillslope treatments resulted in significant changes on AIC(N-OUT) at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC(N-OUT). However, the coarse DEM resolution explained the lack of effect of the rock check-dams - located on the secondary channels - on AIC(N-OUT). AIC(N-OUT) proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.

Automated summary

This study evaluated the impact of forest fires and post-fire practices on sediment connectivity in five Mediterranean catchments in southeastern Spain. By using the 'aggregated index of connectivity' (AIC) analysis, the study assessed the SC in the study area. Results showed that post-fire management practices effectively reduced sediment connectivity, while functional SC was linked to actual changes in SC.