RELATIVE EFFICIENCY OF 3 REPRESENTATIVE MATORRAL SPECIES IN REDUCING WATER EROSION AT THE MICROSCALE IN A SEMIARID CLIMATE (VALENCIA, SPAIN)

In the Mediterranean region, where rainfall is scarce but often of hig h intensity, the matorral vegetation cover provides essential protecti on to the soil against the erosivity of rainfall and reduces considera bly the water erosion rate. Three representative species of the Medite rranean matorral displaying different morphologies (Rosmarinus officin alis, L., Stipa tenacissima, L., Anthyllis cytisoides, L.) were select ed for study at the microscale (plant scale) for their relative effici ency 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 com pared for the three species. The quantification of interrill erosion a nd 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 sample s were also taken in the microenvironment of the plants in order to ev aluate possible differential influences of the three species on soil p roperties relevant to water erosion. The results show that the three s elected species reduced runoff and soil loss in different ways. The 's creen effect' arising from the very dense canopy of Stipa tussocks, re presents an effective way to counteract rainfall erosivity and reducin g splash erosion. However, in the case of Rosmarinus, in addition to t he mechanical protection offered by its canopy and litter covers, the latter (which lies permanently at the soil surface under the plant can opy) improves moreover the topsoil structure because of the important incorporation of organic matter below the canopy cover. The role of li tter cover in controlling erosion seems therefore to be predominant un der Rosmarinus. As for Anthyllis, these deciduous shrubs provide littl e 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 t he improvement of soil properties under their canopy. Thus, in open ma torral (patchy vegetation), fertile soil islands developed below the p lant canopy. These differ considerably from the bare soil inter-plant areas that give rise to higher soil loss rates. (C) 1998 Elsevier Scie nce B.V. All rights reserved.