A convex distribution of vegetation along a stony soil slope due to subsurface flow in the semiarid Loess Plateau, northwest China

摘要

Soil water-vegetation interactions have been a research topic for decades. Landscape patterns can be shaped by soil water availability, and in reverse. The effects of subsurface flow on the soil water - vegetation interactions are relatively less studied than the surface flow, especially in the semiarid region. This work is focused on how the larch (Larbc principis-rupprechtti) interacted with soil water, and how the convex pattern of the larch was formed along the stony soil slope in the semiarid Loess Plateau, northwest China. The soil water balance equation in Soil Water Assessment Tool (SWAT) was modified to include subsurface flow exchange between two adjacent hydrologic response units (HRUs). The slope was then delineated into adjacent HRUs to understand the hydrologic and ecological processes inside the slope. The modified SWAT model on the slope was calibrated and validated by the field data. The model was forced by a 55-year meteorological data series to investigate the larch-soil water interactions and the formation of the convex distribution pattern over long term. It is found that the subsurface flow has shaped the convex distribution of vegetation LAI along the slope. The subsurface flow occurs due to relatively high permeability of the stony soil, and it affects the heterogeneities of soil water availability through the soil water storage capacity. The concave spatial pattern of the soil water stress determines the vegetation growth along the slope in this semiarid region. These understandings provide new knowledge about the influences of hydrological processes on vegetation distribution patterns along a slope, which is useful in vegetation management under similar conditions.