Facilitation Effects of the Rangeland Shrubs Astragalus chrysostachys Boiss and Artemisia kopetdaghensis (Poljakov) Y.R.Ling on the Species Diversity, Along a Gradient of Livestock Grazing

Spiny and aromatic species in rangelands can play important role in the conservation of plant species in rangelands; however, few studies  have been done on the role of these plants under different levels of livestock grazing. In this research, the facilitation effects of spiny (Astragalus chrysostachys Boiss) and aromatic (Artemisia kopetdaghensis (Poljakov) Y.R.Ling) shrubs were studied on species diversity along a grazing gradient. In 2017, five sites were selected in Baharkish rangelands, Quchan, where the livestock grazing varied from low to very intense. In each site, 30 twin plots were established under a canopy of the nurse shrubs and their nearby open spaces. Density, frequency and canopy cover of all plants were measured within the plots. Species diversity were reduced by increasing the grazing intensity, but it was consistently higher under canopy. In the highest grazing intensities, species diversity was higher under the canopy of Artemisia than Astragalus; however, opposite results were found under the high grazing intensity. In conclusion, in the areas of high grazing (livestock rest points), the aromatic species (Artemisia) may not be protected against livestock grazing, and spiny shrubs (Astregalus and Acantholimon) may still maintain their nursing effects.