Delayed application of straw mulching increases soil erosion in Mediterranean pine forests burned by wildfires

Several studies have explored the effectiveness of straw mulching against soil erosion in wildfire-affected forests as post-fire management technique. In contrast, scarce literature exists about the application time of the mulch cover, although this factor - beside climate patterns of the application site - is essential to increase mulching effectiveness. To fill this gap, this study has evaluated the soil loss in two forest sites of Castilla La Mancha (Spain), in which straw mulching was applied in two burned forests immediately after the wildfire or four months after the fire event. These sites show similar characteristics (soil burn severity, soil type, and vegetation), and thus the difference in soil erosion can be attributed to the treatments. The mulching effectiveness has been measured as the difference between the soil loss per unit of erodibility comparing unburned and untreated, and burned and mulched plots. At a comparable rainfall erosivity (difference in EI30 between the two sites lower than 40 %), soil loss decreased by 67 % (in the case of timely distribution) and 33 % (when the action is delayed) in mulched sites compared to the untreated areas. After a rainstorm with very high erosivity (+600 % of EI30), soil loss reduction was equal to 85 % in the case of early mulching application. This higher effectiveness of early mulching compared to the delayed application was due to the quicker post-fire regrowth of vegetation, and the increased level of incorporation of vegetal residues into the soil. This result suggests to land managers that straw mulching should be applied immediately after a wildfire in burned forests, in order to achieve the highest anti-erosive effects. Further research is suggested to validate these results in other environments and after application of other mulches.