Variability of hydraulic conductivity and water repellency of soils with fire severity in pine forests and reforested areas under Mediterranean conditions

The effects of fire on soil hydraulic conductivity (K) and soil water repellency (SWR) have been mainly studied by field experiments in forest areas burned by wildfires with a given severity, while the variability of K and SWR with the fire severities has been less investigated. To fill this gap, the changes in the K and SWR with fire severity and soil depth (1 and 5 cm below the ground surface) have been evaluated in two forest ecosystems (natural stand of pine and reforested areas) of Central Eastern Spain. A significant influence of the fire severity on the infiltration rates was found, and this influence was different between the natural stand of pine and the reforested areas. Compared to the unburned soils, the highest reduction of the K (80% to 90%) and SWR levels were found for the fires with low and intermediate severities at the soil surface. At the lower soil depth, the reduction of K and the SWR level due to fire were proportional to its severity. Moreover, the K of the soil surface layer was often higher compared to the water infiltration in the deeper layer. In the reforested areas, also low fire severities can noticeably reduce the surface K, despite the limited SWR, while the natural forests are less exposed to hydrophobicity in their surface soil layer. This study indicates the need to reduce the risk of flooding and erosion linked to a reduction in water infiltration and increase of soil repellency.