We analyzed the empirical relationship between plant coverage and sediment ratio curves (SR) at two semi-arid Mediterranean sites (inland Spain). Comparison of b values in the fitted equation (SR = a * e −b *x), with x as % cover) shows a significant difference (P < 0.05) between Rosmarinus officinalis, and an association of lichen and Lygeum spartum. We hypothesize that both the architecture of individual plants and the association of plants, could play a key role in partitioning rainfall between stemflow and throughfall. This, in turn, affects soil erosion by water.