the effects of exclosure on plants in the semi-arid rangeland of north khorasan province, iran

abstract over the last fifty years, most of the semi-arid rangeland in iran has been converted to cropland without an equivalent reduction in grazing animals. this shift has led to heavy grazing pressure on rangeland vegetation. the present study has been conducted in sisab research station in the north khorasan province to evaluate effects of long-term grazing exclosures on biodiversity of range plants. the study was initiated in may 2008 using three transects within the exclosure and another three transects near exclosure, each with 100m length in the vicinity of exclosure has been established to determine differences in plant composition between areas that have not been grazed in 22 years with neighboring grazed plant communities. the sampling method was randomized systematic one comprised of 10 plots, each of 1m2 in area. a total of 53 plant species were identified in the study area with the ungrazed plots containing 18 plants more than the grazed plots. the major species were festuca ovina, centurea depressa, stachys turkamanica, stipa barbata, astragalus sp and phelomis cancellata. grazing impacts on forbs were more pronounced than for grasses and shrubs. based on jaccard’s index, there was only a 45% similarity of plant species between the two treatments. our study led to four generalizations about the current grazing regime and long-term exclosures in the semi-arid rangeland around the study area: (1) exclosures will increase species richness, (2) heavy grazing may have removed some plant species, (3) complete protection from grazing for a prolonged period of time after a long history of grazing disturbance may not lead to an increase in desirable plant species with a concomitant improvement in range condition, and (4) research needs to be conducted to determine how these rangelands can be improved.