Variation of rock fragment cover and size along semiarid hillslopes: a case-study from southeast Spain

The spatial variation of rock fragment cover (Rc) and rock fragment size (Rs) along semiarid hillslopes and transects in the Mediterranean is largely controlled by hillslope gradient. Total rock fragment cover (Rc>5 mm) often increases in a convex upward curve with hillslope gradient while the D50 of the surface rock fragments >5 mm increases linearly with hillslope gradient. On south-facing slopes, Rc>5 mm is slightly higher than on north-facing slopes. Lithology controls the size distribution of the stone pavement rather than its cover percentage. Spatial variation of rock fragment cover reflects spatial variation in past erosion and deposition rates. Hillslope sections that are steep, south-facing, or have been abandoned a long time ago have undergone intense interrill and rill erosion, and thus have high rock fragment covers. Tillage erosion leads to high rock fragment covers on convex hillslopes in intensively cultivated areas. Thus, using information on hillslope gradient, aspect, lithology and landuse, we have been able to describe the spatial variation of rock fragment cover and size along semiarid hillslopes in southeast Spain. Such information is crucial for understanding and modelling the spatial variation of the hydrological and erosion response of semiarid hillslopes under environmental change, especially in semiarid environments of the Mediterranean where vegetation cover is predicted to decrease due to climatic or landuse changes and rock fragments at the surface become the only soil surface stabilisers.