干旱区生态环境知识资源中心

Ground surface microtopography and soil penetration resistance play a major role in the geomorphic processes that occur on the hillsides of semi-arid rangelands. Although these two features are known to be impacted by the occurrence of shrub vegetation, the role of livestock remains unclear. The purpose of this study was to determine the impact of livestock on microtopography and penetration depth associated with patches of Sarcopoterium spinosum, a dominant shrub in the northern Negev region of Israel. Soil surface slope and penetration depth were determined for five segments along shrub-centered transects on the hillside axis: under the shrub canopy; upslope (US) and downslope (DS) of the central stem cluster; immediately upslope of the shrub (TR); upper intershrub (UI; above TR); and lower intershrub (LI; below DS). The effect of livestock was determined by comparing values obtained inside and outside 10-year-old exclosures. Livestock presence reduced soil penetration depth from 14.9 to 10.6mm at segment UI, from 16.9 to 5.9mm at segment TR, and from 15.2 to 9.9mm at segment LI. The presence of livestock sharpened the step-like microtopographic profile along the transect: it reduced the incline from 10.2 to 5.7 degrees at segment TR, and from 12.8 to 9.2 degrees at segment US, whereas it increased the incline from 17.8 to 21.2 degrees at segment DS. Such changes increase the spatial discontinuity of the hillside surface and can be expected to influence the spatial redistribution of water and soil resources, and thereby ecosystem functioning and productivity. These results lend credence to the view that livestock can function as physical ecosystem engineers by modulating resource availability to other organisms.