Effects of post-fire mulching with straw and wood chips on soil hydrology in pine forests under Mediterranean conditions

Mulching is one of the most common post-fire management techniques, which has been widely studied at the global scale. However, more research is needed on the hydrological effects of mulching in forest ecosystems under Mediterranean semi-arid conditions. This study has evaluated water infiltration, surface runoff and soil loss using a portable rainfall simulator in Central-Eastern Spain after post-fire treatments. In this area, a large wildfire recently affected a pine forest, and the burned soil was mulched using wheat straw (dose of 0.3 kg/m(2)) or wood chips (2 kg/m(2)) on plots with two different slopes (about 30%, lower slope, and 50%, higher slope). The study has shown that the soil condition (burned control vs. soils mulched with straw or wood chips) and slope (lower vs. higher) did not significantly influence the water infiltration. However, the mean infiltration of the soils mulched with straw were higher (+40% and + 17%, respectively) compared to both the control and the plots mulched with wood chips. Moreover, lower surface runoff (-23%) was measured in the mulched soils compared to the control plots. The soil mulching with straw was more effective at decreasing the runoff coefficient (-31%) compared to plots treated with wood chips (-18%) and the control areas. Soil loss was significantly lower in plots treated using straw (-87% compared to the burned and not treated soils) compared to wood chips (-54%). Peaks of 90-95% of reduction in the soil loss were even recorded in the steeper soils. Finally, we suggest the application of wheat straw rather than wood chips, since the wheat straw mulch material provides a higher soil cover (on average 73% against 48% of wood chips) and therefore is more indicated to reduce the hydrological response in burned soils, as confirmed by the lower runoff (in the average -16%) and erosion (-73%) measured in this experiment on both gentler and steeper soils.