Effects of stand composition and soil properties on water repellency and hydraulic conductivity in Mediterranean forests

This study evaluates soil hydraulic conductivity (SHC) and water repellency (SWR) in three mixed forest stands in relation to site plant and soil characteristics. The studied forest stands were (i) Pinus nigra Arn. ssp salzmannii and Quercus ilex; (ii) P. nigra Arn. ssp salzmannii and Juniperus Thurifera; (iii) P. nigra Arn. ssp salzmannii, Q. ilex and Juniperus Thurifera. A 100- to 120-year-old unmanaged P. nigra Arn. ssp salzmannii stand was also chosen as control. The hydrological variables, physico-chemical properties and surface characteristics of soils were surveyed. Soil water infiltration was higher in Pinus + Juniper mixed forest and Pinus + Quercus + Juniper mixed forests compared to unmanaged Pinus stands. None of the studied forest stands shows a high level of repellency. Only a slight repellency (in unmanaged stands dominated by pines) or moderate repellency (in soils with Pinus and Juniper) were evident, while soils with Pinus and Quercus were not repellent. Differences in SHC among the forest species were driven primarily by the soil texture and associated structure and secondarily by soil organic matter and associated SWR. The latter was mainly due to organic matter content of the soils, but others of the soil physico-chemical properties and covers analysed were found as influencing parameters to discriminate SWR among mono-specific and mixed forest stands. While SHC at the studied forest stands could be predicted using organic matter as well as sand and clay contents of the soil, SWR is the result of several hydrological and physico-chemical parameters.