Spatial heterogeneity of throughfall and its contributions to the variability in near-surface soil water-content in semiarid mountains of China

Throughfall (TF) is one of the most important factors affecting forest surface soil moisture. However, TF heterogeneity and its contributions to the variability in near-surface soil water-content (SWC) in a spruce forest in semiarid mountain ecosystems are poorly understood, and may determine plant survival. Here, we systematically investigated variability of TF in a Picea crassifolia stand within a protected semi-arid mountain ecosystem, and evaluated the contributions of TF to near-surface SWC variability obtained from TF gauges and SWC measurements at the plot level. Results showed that TF variability tended to decline with an increase in rainfall amount, intensity, and duration, and then tended to be stable after a value of 24.1 mm, 3.1 mm h(-1) and 789.8 min, respectively. Both TF and surface SWC were highly spatially variable, but the spatial patterns appeared to be stable over time based on time-stability analysis. The mean SWC increment exhibited a strong positive power relationship with plot mean TF, and the percent of locations with SWC increments increased similarly to TF amount for individual rainfall events. TF, soil bulk density, and litter fall biomass can significantly (P < 0.05) affect the stability of SWC increments. Therefore, our research indicated that further research should consider the relative importance of, and interactions among precipitation characteristics, soil heterogeneity, and vegetation characteristics. Our results may be useful for land managers involved in enhancing the water conservation capacity of semi-arid mountain forest ecosystems, where climatic conditions, soil quality and vegetation characteristics will determine the supply of multiple forest ecosystem functions.