Impact of reforestations with exotic and native species on water repellency of forest soils

Abstract

Forest duff layer is usually water repellent due to the hydrophobic organic compounds resulting from degradation of tree tissues. Transition from hydrophobic to wettable conditions, or vice versa, is largely controlled by water content. The objective of this investigation was to assess the influence of soil moisture on the degree of soil water repellency (WR) in exotic and native tree forests. Occurrence of WR was investigated by the water drop penetration time (WDPT) and the ethanol percentage (EP) tests. Sampling was conducted in the forest soils of two exotic species (Pinus pinaster, P, and Eucaliptus camaldulensis, E), used in the past for reforestation, and two native species (Quercus ilex, L, and Quercus pubescens, R). The WDPT vs. θ relationships exhibited a decreasing trend with a transition from hydrophobic to wettable conditions in the range θ = 0.14 - 0.19 cm3cm-3. The EP vs. θ relationships showed a maximum in the range θ = 0.10 - 0.15 cm3cm-3. Hydrophobicity in soils of native species persisted at relatively higher water content compared to exotic ones and it is expected to influence the hydrological processes to a greater extent.