Effect of exposed roots on the erosion characteristics of sloped land based on close-range photogrammetry in a karst rocky desertification region

Abstract

On sloped land in karst rocky desertification regions, some roots gradually become exposed to the surface due to the low soil-forming rate of the parent rock and shallow natural soil layer. The spatial orientation of these roots varies with the terrain as the plants grow and the surrounding surface erodes. In previous studies, the exposed roots were often used to estimate erosion intensity, but little is known about how exposed roots influence the erosional characteristics of sloped land. In this study, the effects of the orientation of the exposed roots (vertical slope arrangement, parallel slope arrangement, transverse slope arrangement) on the erosion characteristics of sloped land were investigated based on close-range photogrammetry and simulated rainfall experiments. The results showed that there were differences in the responses of the sloped land to erosion based on the different orientations of the exposed roots. In the first four rainfall events, the surface runoff rate was the highest for the parallel slope arrangement, followed by the vertical slope arrangement and transverse slope arrangement. With the occurrence of intermittent rainfall events, this difference gradually decreased. The exposed roots affected the erosional characteristics of sloped land by interfering with the runoff flow path. In most rainfall events, the general trend of eroded sediment yield was parallel slope arrangement > vertical slope arrangement > transverse slope arrangement. The digital elevation model (DEM) constructed by close-range photogrammetry showed that the surface microtopography changed during intermittent rainfall, which resulted in the difference in the relief of sloped land with different exposed root distribution patterns. The volume of soil detached and transported along slopes with parallel slope arrangement was more severe than that on transverse and vertical slopes because the shallow gullies between exposed roots provided a good transport channel for runoff along sloped land. These results provide a reference for understanding the relationship between plant roots and erosion processes in regions of karst rocky desertification.