Livestock redistribute runoff and sediments in semi-arid rangeland areas

摘要

Semi-arid areas where grazing is the main land use exhibit a"three-phase-mosaic" pattern of dominant surface patches: shrubs, tramplingroutes, and intershrub areas. This pattern differs from the "two-phasemosaic" seen in grazing-free semi-arid areas. The patches might create apositive feedback process in which enhanced infiltration beneath shrubsminimizes overland flow from under their canopies, thereby strengthening thesink–source mechanism by which overland flow generated between shrubsrapidly infiltrates into the soil beneath them, where it deposits soilparticles, litter, nutrients and organic matter, thereby enhancinginfiltration by changing the local microtopography, and improving soilproperties. To analyze sink–source relationships among the patches in grazedareas in rangelands of the semi-arid northern Negev region of Israel, weconstructed small runoff plots, 0.25–1.0 m2 in area, of five types:shrub (Sarcopoterium spinosum), intershrub, route, route–shrub combination, andintershrub–shrub combination. The shrubs always occupied the downslope partof the plot. Overland flow and sediment deposits were measured in all plotsduring 2007/8 and 2008/9. The combined plots yielded much less overland flowand sediments than intershrub, routes and shrub ones, indicating that theshrubs absorbed almost all the yields of the upper part of their plots. Theshrubs generated less runoff and sediments than routes and intershrubs;runoff flows from the routes and intershrubs were similar; sediment yieldwas highest in the intershrubs. Thus, runoff yield exhibited a two-phasemosaic pattern, and sediment yield, i.e., soil erosion, a three-phase mosaicpattern.