effects of shrubs on preserving understory plants against the livestock grazing

rangeland shrubs may provide mechanical facilitation on their understory plants, by protecting themagainst the livestock grazing. however, such a facilitation effect may vary depending on the rangelandutilization rate. in a field research, mechanical facilitation of rangeland shrubs was compared in ahighly 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 andslope aspects. forage production was measured by clipping method within the paired plots, i.e. underthe canopy of nursing shrubs and their nearby open areas. in the enclosure site, forage production wassimilar under the canopy of shrubs and in open areas, whereas in the highly and moderately grazedsites there were more forage under the canopies. these results indicate increases in mechanicalfacilitation of rangeland shrubs by increasing the grazing intensity. the mechanical facilitation wasalso varied depending on the life forms of understory species. in the enclosure, the greatest facilitationwas on annual forbs, whereas in the highly grazed site it was on perennial grasses. results of thisstudy show important role of rangeland shrubs on preserving understory forage plant against theintense livestock grazing.