Post-fire Management Effects on Sediment (Dis)Connectivity in Mediterranean Forest Ecosystems: Channel and Catchment Response

Abstract

[Abstract] 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 × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AICоᴜᴛ), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AICɴ₋оᴜᴛ). 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; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AICɴ₋оᴜᴛ. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post-fire practices that reduced SC (x̅ = − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC (x̅ = + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AICɴ₋оᴜᴛ at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AICɴ₋оᴜᴛ. However, the coarse DEM resolution explained the lack of effect of the rock check-dams – located on the secondary channels – on AICɴ₋оᴜᴛ. AICɴ₋оᴜᴛ proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.