Spatial association between rangeland shrubs and perennial grasses

The type of plant-plant interaction has prominent influences on the structure and composition of the natural plant communities. Facilitation between shrubs and their understory plants leads to the positive spatial associations, and hereby enhances the survival rates of the understory plants. We studied the type and extent of spatial association between four rangeland shrubs (Astragalus mesedensis, Artemisia khorasanica, Acantholimon prostegium, and Acantholimon erinaceum) and two perennial forage grasses (Bromus kopetdaghensis, and Festuca alaica) in their natural habitats, Baharkish, Quchan, Iran. Results indicated positive association (facilitation effect) between shrubs and perennial grasses, with no negative association (competition effect) being found for any species pairs. Among the nurse species, A. mesedensis showed greater and Acantholimon species indicated smaller positive association, while A. khorasanica did not show any association with the grasses. Between the beneficiary species, greater association with the nurse shrubs was found for F. alaica than B. kopetdaghensis. Accordingly in this study, A. mesedensis and F. alaica are the best nurse and beneficiary species, respectively. Our findings indicate the important role of nurse shrubs in preserving forage range plants. These results can also be used in the rangeland restoration projects, especially for seeding forage plants under the canopy of nurse shrubs.