The effect of grazing on soil and water losses under arid and mediterranean climates. Implications for desertification

Two sites, both affected by grazing but under different climatic conditions, were selected in Israel to study the effect of grazing on soil degradation. One site was selected in the Judean Desert, a dry environment (260 mm mean annual rainfall) with a long history of overgrazing and very little vegetative cover. The second site was selected in the Galilee Mountains where the climate is of Mediterranean type (650 mm mean annual rainfall) and the vegetative cover is much greater in spite of the grazing. Simulated rain experiments were performed in the field and in the laboratory in order to evaluate differences in hydrological and erosional response to rainfall between the two sites. The results show a clear difference between these two ecosystems. In the Judean Desert, where vascular plant cover is sparse, a crust was developed which enhanced overland flow and erosion. In the Mediterranean environment the overland flow and erosion were negligible under shrubs and relatively high at the intershrub corridors. At the hillslope scale a mosaic-like pattern of water and soil contributing and accepting patches was developed. Such a pattern usually protect the hillslope from being eroded. Runoff and erosion rates were very high in the Judean Desert and negligible in the Galilee Mountains.