Influence of oak trees on soil hydraulic characteristics: A spatial analysis in a Mediterranean silvo-pastoral ecosystem

• Trees significantly increase soil saturated hydraulic conductivity (K s ). • K s decreases with distance from the tree trunk in oak-wood grasslands. • Field-scale assessments miss fine-scale soil–water variability. • Single-point K s measurements do not capture tree effects. Accurate prediction of soil water movement in complex environments requires detailed knowledge of the spatial and temporal variability in soil hydraulic properties, in particular hydraulic conductivity. The study presents the results of a field campaign documenting topsoil hydraulic properties at an oak-wood grasslands (WG) in a Mediterranean ecosystem in Sardinia (Italy), a vulnerable ecosystem endangered by climatic and land-use changes. Emphasis is provided to the impact of the trees on soil hydraulic properties, through the assessment at the field complemented by a detailed investigation at the individual-tree spatial scale. Particle size distribution, organic matter, and dry bulk density were sampled, and infiltration evaluated through Beerkan tests using single-ring automated infiltrometers. The data was processed with a recently proposed fractional wettability infiltration model to derive saturated hydraulic conductivity ( K s ). Results revealed a complex spatial pattern of soil hydraulic properties strongly influenced by the tree presence. Mean K s under canopy (U) was 376.6 mm h −1 , approximately 2.3 times higher than in adjacent open areas (O). Detailed measurements below and around an individual oak showed similar mean K s values but also highlighted a spatial gradient in the K s distribution, with the highest and more variable K s values near the trunk and a progressive decline outward. Notably, the outermost under-canopy positions showed K s values comparable to those detected in the first meters of the adjacent open area, suggesting that tree influence may extend beyond the canopy projection. The results suggest that the sampling strategies of the hydraulic soil properties should account for the fine-scale tree-induced heterogeneity for obtaining representative estimations. Incorporating this fine-scale variability into hydrological models can improve simulations of soil–water processes and enhance predictions of how land-use changes, for example induced by land abandonment, affect hydrological dynamics in tree-dominated Mediterranean ecosystems.