HYDROLOGIC IMPLICATIONS OF POST-FIRE MULCHING ACROSS DIFFERENT SPATIAL SCALES

Besides direct damage, wildfires can produce striking direct and indirect impacts, including extreme runoff-erosion responses with serious negative consequences for land-use sustainability and downstream values at risk. The best way to reduce post-fire runoff is the rapid application of mulch: a protective cover of straw, needles, wood-based material, or other ground cover. In this study, we assessed the efficacy of forest residue mulching for reducing post-fire runoff across spatial scales on a logged and burnt eucalypt hillslope. Additionally, we assessed the underlying processes involved in the hydrologic responses of burnt areas in central Portugal during the first 2 years after a wildfire, with special focus on soil moisture, soil water repellency, and rainfall. Forest residue mulch reduced post-fire runoff by 50% in both micro-plots (0.25 m(2)) and hillslope scale silt fence plots (100 m(2)) during the first year after the wildfire. Runoff in the micro-plots was tenfold higher than the larger plots, regardless of mulching. The main controlling factors for the volume of runoff were rainfall amount (direct correlation) and soil moisture (inverse correlation). Soil water repellency and soil moisture were not affected by the mulch but played a role in the hydrologic response. In contrast, there was no decrease in runoff rate within the first two post-fire years. Forest residue mulching can be an effective postfire treatment for reducing runoff rates, and the consistent decrease in runoff rates between the two spatial scales suggests that the scaling of runoff was not affected by the mulch. Copyright (C) 2015 John Wiley & Sons, Ltd.