Surface microtopography and soil penetration resistance associated with shrub patches in a semiarid rangeland

The surfaces of hillsides in semiarid regions are characterized by vegetative patchiness and an associated pattern of soil characteristics. In a semiarid patchy rangeland in the northern Negev region of Israel, the pattern of ground surface microtopography and soil penetration resistance were investigated along transects centred on randomly selected shrubs of Sarcopoterium spinosum. Each transect comprised five segments on the hillslope axis: upslope (US) and downslope (DS) of the central stem cluster of the shrub patch, immediately upslope of the shrub (TR), an upper intershrub (UI) segment (above TR), and a lower intershrub (LI) segment (below DS). Significant differences were found among the different segments, with regard to both slope and soil penetration resistance. Segment US had a relatively shallow slope (9.0° in average) and the deepest penetration depth (20.5 mm). Segment DS had the steepest slope (21.0°) and a relatively deep penetration depth (16.4 mm). Segments UI and LI had intermediate values for both slope (15.1° and 13.4°, respectively) and penetration depth (10.5 and 9.8 mm). A spatial relationship between the shrub patches and grazing was found: segment TR, immediately above the shrub, tended to be a flock trampling route and had the lowest values of both slope (5.1°) and penetration depth (6.1 mm). A conceptual model was proposed to explain these results; it suggests that under the prevailing conditions of the study site these relationships regulate the redistribution of soil resources on the hillside.