Livestock redistribute runoff and sediments in semi-arid rangeland areas

Semi-arid areas where grazing is the main land use exhibit a ''three-phase-mosaic'' pattern of dominant surface patches: shrubs, trampling routes, and intershrub areas. This pattern differs from the ''two-phase mosaic'' seen in grazing-free semi-arid areas. The patches might create a positive feedback process in which enhanced infiltration beneath shrubs minimizes overland flow from under their canopies, thereby strengthening the sink-source mechanism by which overland flow generated between shrubs rapidly infiltrates into the soil beneath them, where it deposits soil particles, litter, nutrients and organic matter, thereby enhancing infiltration by changing the local microtopography, and improving soil properties. To analyze sink-source relationships among the patches in grazed areas in rangelands of the semi-arid northern Negev region of Israel, we constructed small runoff plots, 0.25-1.0 m(2) in area, of five types: shrub (Sarcopoterium spinosum), intershrub, route, route-shrub combination, and intershrub-shrub combination. The shrubs always occupied the downslope part of the plot. Overland flow and sediment deposits were measured in all plots during 2007/8 and 2008/9. The combined plots yielded much less overland flow and sediments than intershrub, routes and shrub ones, indicating that the shrubs absorbed almost all the yields of the upper part of their plots. The shrubs generated less runoff and sediments than routes and intershrubs; runoff flows from the routes and intershrubs were similar; sediment yield was highest in the intershrubs. Thus, runoff yield exhibited a two-phase mosaic pattern, and sediment yield, i.e., soil erosion, a three-phase mosaic pattern.