Effect of the Litter Layer on in Situ Water Repellency and Moisture Conditions of Surface Mineral Soil Under a Humid-Temperate Forest

Surface soil under forests often shows soil water repellency (SWR). The litter layer and the SWR are both well known to affect water movements in hillslopes, yet little is known about their interaction. In this research, we established litter removal and litter remaining (control) plots in the same slope, which had developed thick litter layers, and repeatedly measured in situ SWR and moisture content of surface mineral soil at multiple points in each plot. We calculated the percentage of water repellent points (SWRarea) and found lower SWRarea and higher soil moisture content in control plots. SWR was more spatially variable in control plots; some measurement points frequently showed SWR, and others were almost always wettable. The frequently water repellent points were drier than those frequently wettable. Litter removal plots, on the other hand, showed large SWRareas more often than control plots. These findings imply that litter layers could reduce surface runoff via decreasing in situ SWR and cause preferential water flow by maintaining both SWR and wettable regions