effects of the canopy of perennial plants and livestock utilization rates on the density of soil seed bank in an arid steppe rangeland

the study of soil seed bank provides useful information on management and restoration of natural ecosystems. in the arid environments, some perennial plants may cause accumulation of seed bank under their canopy, thereby protecting them against the livestock herbivory and the other environmental factors. this study was conducted with objective to investigate effect of perennial plants on density of soil seeds bank, under different utilization levels in an arid steppe rangeland.  three adjacent rangeland sites were selected, i.e. intense grazing, moderate grazing and no grazing (enclosure), and three line transects were randomly located within each site. along each transect, soil samples were taken from the depth of 0–5 cm under the canopy of perennial plants or the nearby open space. the seed bank density was determined by the technique for separating seeds from the soil. the density of soil seed bank in the moderate and intensive grazing sites was higher than in the enclosure. in addition, seed bank density under the canopy of perennial plants was significantly higher than in open space, in each of three sites. the highest and lowest seed bank density were observed under the canopy of rosa persica and astragalus heratensis, respectively. generally, the results of this research indicate the key role of perennial range plants in protecting soil seed bank of other plants, under the circumstances of high livestock grazing in the arid steppe rangelands.