Telling a different story: The promote role of vegetation in the initiation of shallow landslides during rainfall on the Chinese Loess Plateau

Vegetation is widely used for controlling landslides around the world; however, rainfall-induced shallow landslides occur frequently on vegetation-covered slopes on the Chinese Loess Plateau during the rainy season. To probe this phenomenon, we conducted on-site investigations and measurements in the Nanxiaohegou catchment on the Loess Plateau to explore the effects of soil properties and vegetation on shallow loess landslides. Most of the loess landslides on vegetation-covered slopes were small scale with depths ranging from 0.3 m to 1.0 m, corresponding to the topsoil being saturated due to rainfall. Majority of shallow landslides occurred on herbage-covered area, which made up 69% of total landslides. There are significant differences in soil properties between the upper layer (root-soil composite) and the lower layer (loess) of the sliding surface. Our study demonstrated that root plays a leading role in landslide erosion and that the most adverse effect of vegetation on landslides is mainly the increase in soil moisture content in the shallow soil through the root zone creating preferential infiltration flow paths. There are remarkable differences in landslide erosion depths and landslide erosion intensities among different vegetation types. The landslide erosion depth and landslide erosion intensity increased linearly with increasing main root depth, indicating that the vegetation root depth determines the landslide erosion intensity during rainfall. Therefore, the potential implications of vegetation especially the herbage to promote landslide occurrences during rainfall should be given more attention in the future.