Depth-Dependent Effects of Dominant Tree Species on Soil Hydraulic Conductivity

The saturated hydraulic conductivity (Ks) of soil is a key parameter governing ecohydrological processes in forest ecosystems. However, quantifying the independent contribution of dominant tree species to Ks remains challenging due to environmental confounding, and the vertical limits of these biological effects are often overlooked. This study analyzed the effects of four major species groups (Pinus densiflora, oak species, other conifers, and other broadleaf species) on Ks at 10 cm and 30 cm soil depths across 5297 sites in Korea, using inverse probability weighting to adjust for environmental covariates. The results revealed that the influence of vegetation is fundamentally depth-dependent. In the topsoil (10 cm) layer, the other broadleaf species group exhibited significantly higher Ks than the other groups, suggesting a consistent association with enhanced surface permeability within the context examined. By contrast, in the subsoil (30 cm) layer, direct species effects diminished, and hydrological functions were governed by complex interactions with environmental factors. These findings suggest that while species selection is a viable strategy for managing surface infiltration, subsoil hydrological functions are constrained by site-specific environmental contexts rather than species traits alone.