Soil depth and recovery interval mediate soil water repellency under different forest types and fire intensity levels in China: Evidence for ecosystem resiliency

Soil water repellency (SWR) is a physical phenomenon whereby the surface of soil particles cannot be, or resists being, moistened by water. The recovery process of fire-induced SWR can provide important evidence for ecosystem resilience, but most existing studies ignored this process. Prescribed burning is a widely used method to reduce the risk of fire and fuel. However, prescribed fires can increase SWR, reducing infiltration and increasing overland flow and subsequent soil erosion. In order to understand the ecosystem resilience process from fire-induced SWR, soil samples were collected before and after prescribed burning. Four different forest types in the Hunan province of China were studied. Soil samples at four different soil depths (0-5, 6-10, 11-15, and >15 cm) and four time intervals (3, 30, 180, and 360 d) after burning at different intensities were collected. No significant difference in SWR was found among the four forest types, but the SWR of soil in plantations was stronger than that in secondary forests before fire. Most soil samples showed slightly increased SWR after burning, SWR increasing with fire intensity. Surface soil (0-5 cm) SWR showed greater sensitivity to fire disturbance than subsurface soil (>5 cm). SWR had a smaller scope of influence and shorter recovery period in burned secondary forests. Although SWR recovered over time, recovery was slower with increasing fire intensity. SWR always recovered to pre-fire levels given sufficient time. Our study revealed the recovery process of SWR, and explored the temporal and spatial mechanisms of forest ecosystem recovery after prescribed burning.