The Spatial Pattern and Temporal Stability of the Soil Water Content of Sloped Forestland on the Loess Plateau, China

Soil water content (SWC) has a key role in the hydrological process and the distribution of vegetation in arid and semiarid regions. Understanding the temporal stability of SWC across a whole hillslope can help to better determine SWC dynamics and to understand changes in stable patterns of SWC affected by vegetative restoration. This study analyzed the temporal stability of the SWC distribution pattern at eight soil depths at intervals of 0.2 m based on 21 locations up a hillslope planted with Chinese pine (Pinus tabulaeformis Carr.). The dominant influencing factors responsible for the temporal stability of SWC distribution pattern during two periods (during 1 yr and during the rainy season) were examined. The results showed that the mean SWCs at each soil depth were low and showed moderate variability. The SWCs followed a normal distribution at each soil depth for each individual measurement. The SWC spatial pattern at each soil depth showed strong temporal stability for the two study periods. The temporal persistence of SWC generally showed an upward trend with increasing soil depth. The temporal stability of the SWC spatial pattern during the rainy season was stronger than that during the full year. The best representative location of SWC changed with soil depth, and the number of representative locations in different soil depths was not constant. The spatial mean SWCs could be estimated accurately by the best representative locations. The mean relative difference in SWC indicated a significant correlation only with soil particles and roots for both periods (p < 0.01). Elevation and soil organic C were the dominant factors influencing the temporal variability of SWC during the full year and during the rainy season, respectively. However, it is currently unfeasible to predict representative locations based on key influencing factors.