Astragalus ovinus Boiss. Responses Along the Gradient of Environmental Factors in Oak Forests of Yasouj, Iran

Environmental factors have a major impact on the distribution and yield of plant species. For this purpose, considering the importance of Astragalus ovinus (L.) Boiss. in forage production and the possibility of using it in improvement and reclamation of forest ecosystem. In the present study, the responses of A. ovinus were evaluated to some environmental factors in one of its habitats of southwest of IRAN (Kohgiluyeh and Boyer-Ahmad province) in 2018- 2020. Redundancy Analysis (RDA) and Generalized Additive Models (GAM) were used to determine the ecological factors affecting vegetation changes and to evaluate the response of A. ovinus along the gradients of  ecological factors, respectively. Data analysis was performed using SPSS17 and CANOC4.5 software. According to the results, the response pattern of A. ovinus along the gradient of soil surface litter, percentage of bare soil, percentage of land slope, and altitude, followed the unimodal model and the optimum growth levels for these factors were 20%, 20%, 30%, and 2220 m, respectively. Also, the response of this species to aspects has followed the unimodal model, so that in the eastern and western slopes, the presence of the species increased and the northern, southern slopes of the species decreased. The reaction of this species to changes in soil sand content followed the bimodal model indicatinga competitive constraint along the environmental gradient. The results of the A. ovinus phenology study showed that the best time for livestock to use of this species is mid-May and the best time to collect seeds of this species is late June to the first half of July. Percentage of canopy cover in forest it has not affected the performance and frequency of this species. Regarding the response of this plant to the gradient of studied environmental factors, it is recommended to pay attention to its habitat characteristics and ecological requirements in improvement programs on oak forests understorey vegetation.