Effects of vegetation restoration on the spatial distribution of soil moisture at the hillslope scale in semi-arid regions

Soil moisture is important for plant growth in semi-arid ecosystems. In this study, spatial variations in soil moisture at depths of 0–6 m on seven hillslopes of Chinaʹs Loess Plateau planted with korshinsk peashrub were analyzed based on soil moisture observations. The objective of this study was to compare the spatial patterns in soil moisture in shallow and deep soil layers at the hillslope scale under the influence of large-scale vegetation restoration. The results showed that: (1) the topographic wetness index was positively correlated with soil moisture near the surface (0–1 m), but negatively correlated with soil moisture at depths below 2 m; and (2) the negative relationship was found between biomass and soil moisture content in deep layers. Soil moisture in shallow layers was more likely to be affected by topographic factors. However, comparisons of soil moisture at different slope positions indicated that the effect of topographic factors on the variability of deep soil moisture was altered, mainly because plants with different biomasses may differ in their consumption of soil water and thus cause greater spatial variations in deep soil moisture. The introduced vegetation may alter the spatial pattern of deep soil moisture influenced by topographic factors at the hillslope scale, and the biomass may have a determining role in the spatial variation of deep-layer soil moisture content.