Effects of Shrubs on Preserving Understory Plants against the Livestock Grazing

Rangeland shrubs may provide mechanical facilitation on their understory plants, by protecting them against the livestock grazing. However, such a facilitation effect may vary depending on the rangeland utilization rate. In a field research, mechanical facilitation of rangeland shrubs was compared in a highly grazed, a moderately grazed and an enclosure site; in an arid rangeland, Kakhak, Gonabad, Iran, during spring to summer 2011. Twenty line transects were established in various directions and slope aspects. Forage production was measured by clipping method within the paired plots, i.e. under the canopy of nursing shrubs and their nearby open areas. In the enclosure site, forage production was similar under the canopy of shrubs and in open areas, whereas in the highly and moderately grazed sites there were more forage under the canopies. These results indicate increases in mechanical facilitation of rangeland shrubs by increasing the grazing intensity. The mechanical facilitation was also varied depending on the life forms of understory species. In the enclosure, the greatest facilitation was on annual forbs, whereas in the highly grazed site it was on perennial grasses. Results of this study show important role of rangeland shrubs on preserving understory forage plant against the intense livestock grazing.