The impact of soil water repellency on soil hydrological and erosional processes under Eucalyptus and evergreen Quercus forests in the Western Mediterranean

Abstract

Forest areas of the Mediterranean regions of Portugal, Morocco, and Tunisia are suffering major land use changes, with the replacement of traditional evergreen Quercus species (i.e. Quercus suber and Quercus ilex) by fast-growing Eucalyptus species. Since Eucalyptus species are amongst those with a higher impact on soil water repellency, this study examined the effect of the replacement on soil properties, water repellency, and on soil hydrological processes and erosion rates. Measurements were performed in areas that correspond to the climatic distribution of evergreen Quercus suber: at Mação and Portel in Portugal; Ben Slimane in Morocco; and Cap Bon, Sousse, and Ain Snoussi in Tunisia. Soil superficial characteristics, including vegetation and litter cover, organic matter content, soil compaction and shear strength, and water repellency were measured for evergreen oak and Eucalyptus stands and related to soil erosion rates and soil hydrological processes. The data are based on the spatial distribution of properties assessed through the use of intensive spatial sampling and on rainfall simulations to address soil hydrological and erosional processes. The results show very different wetting patterns for some of the Eucalyptus stands during dry and moist periods, as a result of strong hydrophobic characteristics following dry spells. Nevertheless, the Eucalyptus stands in semi-arid climate show no sign of water repellency, which contradicts the theory that water repellency is purely a result of dry conditions. The experiments show no significant increases on overland flow amounts and erosion rates as direct result of soil water repellence (hydrophobicity) characteristics.

Eucalyptus reforestation induces soil water repellency

“…Although this result is not unexpected given the widespread nature of water repellency on agricultural soils in this region (Blackwell 2000) and previous reports of water repellency associated with eucalypts, it has not been quantified in southern Australia, despite >0.5 Mha of eucalypt reforestation in the last two decades (Gavran 2013). Although water repellency has been previously reported in E. globulus plantations in Portugal (Doerr et al 1998;Ferreira et al 2000;Coelho et al 2005; Rodríguez-Alleres and Benito 2011), a feature of those studies was that the different land uses were geographically distant with uncontrolled soil and site differences, whereas in this study, the result is based on paired sites in which these differences are minimised. Indeed, analysis of soil characteristics at paired sites demonstrated no difference in other soil properties, strengthening the conclusion that repellency was induced via eucalypt reforestation.…”

“…Water repellency reduces the infiltration capacity of soils and is often associated with increased runoff and erosion (Witter et al 1991;Ferreira et al 2000;Shakesby et al 2000;Doerr et al 2003;Coelho et al 2005). Preferential flow patterns can be established because of the presence of water repellency, which through finger-flow increases the likelihood of harmful substances being leached into groundwater (Bauters et al 1998).…”

Soil Erosion Under Different Land Use and Cover Types in a Marginal Area of Portugal

“…The highest values were detected in the top layer of the recovering oak and pasture land plots. Under very wet conditions, all the soils were hydrophilic, which agrees with the finding of Coelho et al (2005). Under dry conditions, the shrubland and Quercus pyrenaica woods showed water repellency, which was more pronounced in the tree formation.…”

Propiedades hidrológicas del suelo y exportación de sedimentos en dos microcuencas de la Cordillera de la Costa en el sur de Chile con diferente cobertura vegetal

“…Entre los diversos impactos geomorfológicos e hidrológicos asociados a la hidrofobia caben destacar (De Bano 2000: a) reducción de la infiltración e incremento de la escorrentía; b) desarrollo de vías preferenciales de infiltración y percolación de agua; c) efectos sobre el régimen de humedad del suelo y propiedades físicas; d) contribución hídrica a cauces, y e) fomento de los procesos erosivos (Contreras y Solé 2003). Se ha documentado que la hidrofobia es una propiedad común en suelos forestales plantados con especies de los géneros Eucalyptus y Pinus, siendo particularmente severa durante las condiciones de sequía de verano (Ferreira et al 2000, Scott 2000, Gerke et al 2001, Buczko et al 2002, Wahl et al 2003, Coelho et al 2005.…”