Use of Mediterranean legume shrubs to control soil erosion and runoff in central Spain. A large-plot assessment under natural rainfall conducted during the stages of shrub establishment and subsequent colonisation

The revegetation of land that is no longer cultivated helps reduce soil erosion and runoff. Prior studies have determined the effectiveness of shrub-type cover for this purpose in Spain using small plots sustaining the growth of mature shrubs without considering scaling effects or the establishment and colonisation period, in which the risk of soil erosion is high. In addition, these studies have assessed the effects of high magnitude–low frequency simulated rainfall. The aim of the present study was to measure under natural rainfall conditions the effects of three shrub covers (Colutea arborescens, Dorycnium pentaphyllum and Medicago strasseri) on runoff and soil loss. Plots 20.2 m × 4 m were created and runoff discharge and sediment concentrations were measured after each rainfall event for 2.5 years (establishment period) and for the following 4 years when the shrubs were well-developed. The results of this experiment were compared with those of a previous study, in which the same data were recorded under conditions of simulated high-intensity rainfall in small plots (0.25 m2). In the control plot (bare soil), 5 rainfall events were responsible for 85% of the erosion (37.5 Mg ha−1) and 59% of the runoff (128.8 mm) produced. When the shrub covers were mature, runoff and erosion were reduced (by 84–95% and 95–99% respectively) compared to the establishment period. The effects of the shrubs at mitigating soil and water losses were more pronounced following high intensity rainfall events. Compared to smaller plots, the 80.8 m2 plots tested here showed similar soil losses under high intensity thunderstorms but runoff losses were much lower, suggesting that some of the runoff reinfiltrates the slope due to shrub distribution effects.