Relative efficiency of three representative matorral species in reducing water erosion at the microscale in a semi-arid climate (Valencia, Spain)

Abstract

In the Mediterranean region, where rainfall is scarce but often of high intensity, the matorral vegetation cover provides essential protection to the soil against the erosivity of rainfall and reduces considerably the water erosion rate. Three representative species of the Mediterranean matorral displaying different morphologies ( Rosmarinus officinalis, L., Stipa tenacissima, L., Anthyllis cytisoides, L.) were selected for study at the microscale (plant scale) for their relative efficiency in reducing water erosion on slopes. The mechanical protection of the soil against raindrop detachment, and the improvement of the soil properties by the biological influence of an isolated plant, were compared for the three species. The quantification of interrill erosion and splash erosion rates under natural rainfall conditions was obtained using erosion microplots of individual plants, and splash cups placed at different distances from the plant axis, respectively. Soil samples were also taken in the microenvironment of the plants in order to evaluate possible differential influences of the three species on soil properties relevant to water erosion. The results show that the three selected species reduced runoff and soil loss in different ways. The `screen effect' arising from the very dense canopy of Stipa tussocks, represents an effective way to counteract rainfall erosivity and reducing splash erosion. However, in the case of Rosmarinus, in addition to the mechanical protection offered by its canopy and litter covers, the latter (which lies permanently at the soil surface under the plant canopy) improves moreover the topsoil structure because of the important incorporation of organic matter below the canopy cover. The role of litter cover in controlling erosion seems therefore to be predominant under Rosmarinus. As for Anthyllis, these deciduous shrubs provide little physical protection against the energetic impact of rain at the soil surface as compared to a bare surface. Nevertheless, the three plant species have a positive influence on their microenvironment, through the improvement of soil properties under their canopy. Thus, in open matorral (patchy vegetation), fertile soil islands developed below the plant canopy. These differ considerably from the bare soil inter-plant areas that give rise to higher soil loss rates.