The effect of patchy distribution ofStipa tenacissimaL. on runoff and erosion

In south-east Spain, a semi-arid area,Stipa tenacissima(alphagrass) covers large natural and semi-natural areas with a mosaic of tussocks and bare zones. However, little knowledge exists about the influence of these patterns on runoff and erosion. In order to understand the hydrological and erosional behaviour of the vegetated (herbs andalphagrass) and bare zones, rainfall simulation experiments were carried out at three sites in south-east Spain. The experiments showed that surface runoff and erosion is negligible in the tussock and quite high in the bare areas. High infiltration rates and deep wetting fronts were measured in the vegetated patches, and lower infiltration rates and shallower wetting fronts in the bare patches. These results lead to the conclusion that patchy distribution ofStipa tenacissimaallows a system for water redistribution. Therefore, the landscape can be divided into bare runoff (water source area) and tussock runon (water sink area) zones.