The impact of straw mulching and salvage logging on post-fire runoff and soil erosion generation under Mediterranean climate conditions

Abstract

Forest fires-affected landscapes enhance sudden runoff discharges, high sediment loads and extreme soil erosion rates. Different soil stabilisation treatments, such as mulching, can be applied to avoid runoff and soil erosion after wildfires. To characterise the post-fire soil erosion rates and runoff generation, we selected a Mediterranean forest affected by a wildfire in Lietor (Spain) to determine the sediment yield (dry sediment (DS), total suspended sediment (TSS), total dissolved sediment (TDS)) and runoff discharge in twelve 200 m2 (10 × 20 m) plots. Immediately after the wildfire, six plots were covered by straw and six other plots were set up as controls. Three months after the wildfire, logging activities were performed and the experimental designs were as follows: mulching + logging (three replicates), non-mulching + logging (three replicates), non-mulching + non-logging (three replicates) and mulching + non-logging (three replicates). During the period after wildfire and before salvage logging, the straw mulch controlled the soil erosion rates (DS, TSS and TDS) versus the non-mulched plots, but straw had no real impact on runoff discharge. For the period after salvage logging, once again runoff did not differ when comparing all the treatments. DS was higher in the non-mulched and non-logging plots, whereas the highest TSS was found in the non-mulched plots (in logged or non-logged plots). TDS was higher in the mulched and non-logged plots. We conclude that straw mulch is efficient management in recent fire-affected mountainous terrains to control soil loss immediately after wildfire. Moreover, logging operations done 3 months after wildfire did not necessary generate higher DS, TSS, TDS rates, mainly because of the type of machinery used for forest operations.