Spatial Gradients of Intensity and Persistence of Soil Water Repellency Under Different Forest Types in Central Mexico

Organic residues release hydrophobic compounds to the soil that may induce soil water repellency (WR), which may inhibit infiltration and increase runoff and soil loss rates. Although there are many studies on soil WR through the world, very few investigations have been conducted in Mexican areas. This paper studies the natural background of soil WR in soils from central Mexico under representative forest types, analyzing the spatial distribution of soil WR in relation with tree canopy, vegetation cover and main soil chemical (pH, CaCO3, organic C content and exchangeable cations) and physical properties (texture). The water drop penetration time and the ethanol tests were used to assess persistence and intensity of soil WR, respectively. Although soil WR was not related with soil properties, it decreased strongly from soil below the canopy of conifers to soil below oaks. When different types of vegetation cover were considered, the proportion of water-repellent soil increased following the sequence: bare soil<shrubs and herbaceous plants<shrubs<trees from fir, fir-pine-oak and pine-oak forest. We found an inverse relation with distance to the tree trunks, contributing to create a patchy pattern of soil WR, with soils under the canopy of conifers showing the most severe WR levels. The spatial distribution of soil WR is also conditioned by microclimatic gradients, as persistence and intensity of soil WR were usually lower in shaded areas (upslope transects from the tree trunks), where soil moisture content is expected to be higher on average through the year. Copyright (c) 2016 John Wiley & Sons, Ltd.