Effects of moderate sheep stocking on plant populations of a Black oak-Bluebush association

Abstract

Investigations aimed at improving analysis and description of vegetation changes during long-term stocking in arid areas are described. A hypothesis that vegetation change will be patterned as is stocking pressure over an area is examined. In arid areas, this implies radial gradients about a water point. An area of arid zone vegetation was selected, described floristically, and sampled for species incidence and density through an arc of 110° at ranges up to 2000 yd from a dam. Significant linear regressions describe relationships for several species between density and radial distance from water. Similarly a map can be constructed on an analysis which shows the strengths and direction of influences on species incidence; this pattern is concentric on the water point. It appears that vegetation changes consequent on grazing agree with the original hypothesis, and are susceptible to improved description by regression equations and other statistical analyses leading to precise quantitative mapping. The implications of these results are discussed.