Studying the Effect of Index Species Astragalus ammodendron on Associated Plants Agropyron tauri and Bromus tomentellus from Different Aspects (Case Study: Arak Province-Shazand, Iran)

The aim of this research was to investigate the effect of index species, astragalus ammodendron on the associated plants of agropyron tauri and bromus tomentellus from different aspects in shazand rangeland in southwest of markazi province. the effects of species density and distribution pattern and then index species on the soil properties were studied. based on the randomized – systematic method, 4 transects with a length of 50 m were established. to find the relationships between index and associated plants, 30 points were randomly chosen along the transects and the number of species was counted from these points to a 50 cm distance in different aspects. along the transects, the distribution pattern of index plants and their presence and absence were determined. to find the effects of index species on soil properties, soil samples were taken and soil properties were determined in laboratory. data were analyzed using spss software. the results showed that astragalus ammodendron density with agropyron tauri and bromus tomentellus were similar to the east and west aspects and near distances. astragalus ammodendron distribution pattern was randomized with a tendency toward the clumped pattern. the effect of astragalus ammodendron on the soil characteristics was not significant except for the north aspect. generally, it is concluded that the effect of astragalus ammodendron (index species) on agropyron tauri and bromus tomentellus densities was not significant.