Effects of Soil Physical Properties on Soil Infiltration in Forest Ecosystems of Southeast China

Soil infiltration properties (SIPs) are important components of forest hydrological responses; however, few studies have investigated the mechanisms through which soil physical properties affect SIPs. In this study, two SIPs, the initial infiltration rate (IIR) and saturated hydraulic conductivity (Ks), were quantified at five soil depths (0–10, 10–20, 20–30, 30–40, and 40–50 cm) in three forest stands (pine (Pinus taeda), oak (Quercus acutissima), and bamboo (Phyllostachys edulis) forests). We constructed a structural equation model (SEM) to analyze the main physical properties affecting the SIPs and their influence pathways, and the results show that the IIR and Ks values for the whole soil profile decreased as follows: pine forest > oak forest > bamboo forest. Soil total porosity (STP), soil field capacity (SFC), capillary water holding capacity (CMC), saturated water capacity (SWC), and initial soil water content (ISWC) were positively correlated with the SIPs, while soil bulk density (SBD) was negatively correlated with the SIPs. The SEM indicated that the main positive driver of soil infiltration was STP, while the sand content and SBD reduced soil infiltration. Soil texture indirectly affected SBD by mediating STP, and SBD indirectly affected the SIPs through SWC. These results provide data that support the simulation of subsurface hydrological responses in forests and have significant implications for forest management.