A Study on Nursing Role of Astragalus brachycalyx Fisch on the Soil Seed Bank under the Livestock Grazing in Summer Rangelands of Boyer Ahmad County

The study of soil seed bank provides vital information for rehabilitation and restoration of rangeland ecosystem. In the arid and semi-arid environments, shrub 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 Astragalus brachycalyx on composition of soil seeds bank, in two area of enclosure and under grazing. For this purpose, sampling of soil seed bank under the canopy of this species and its open space adjacent was measured using a flexible plot along the 100 meters transect. Soils were sampled from 0-5 and 5-10 cm depths. Then seed bank composition was identified after seed germination in glasshouse. The results showed that 16 species under the canopy of Astragalus brachycalyx and 12 plant species in the open space adjacent in enclosure area and 21 species under the canopy of Astragalus brachycalyx and 11 plant species in the open space adjacent in under grazing area. In the soil seed bank of an area under the livestock grazing and understory of Astragalus brachycalyx, the species namely Silene longipetala, Mentha longifolia, Veronica anagallis-aquatica and Anthemis odontostephana had the greatest numbers of seeds respectively. The area under livestock grazing had higher density of seed bank of plants with annual and perennial life, Therophytes and Hemicryptophytes biological forms, annual and perennial vegetative forms of forbs, and palatable classes II and III in understory compared to the open space.