Developing response curves for Astragalus verus Olivier with respect to the environmental gradients in Fereydounshahr region of Isfahan province using none parametric multiplicative regression

This study was carried out in an attempt to develop a response curve for Astragalus verus Olivier with respect to some environmental gradients using None Parametric Multiplicative Regression (NPMR) method. The potential distribution maps of the species in Fereydunshahr rangelands of Isfahan province were developed using Logistic Regression (LR) and Ecological-Niche Factor Analysis (ENFA) methods. To construct these two models, thirty one environmental variables (including edaphic, climatic, and physiographic variables) in the studied area were mapped. Then, drawing on these maps and the maps of the environmental variables, NPMR approach was used to provide a response curve for the species. The predictive NPMR models can provide response curves for species against various environmental gradients without any assumed pattern and can determine the ecological amplitude of the species. The results obtained from the maps of the potential habitats (LR and ENFA) and the response curve indicated that the appropriate habitat for Astragalus verus in the region under study was an area with moderate to relatively heavy soil texture (44 to 48 percent clay content), moderate slope (10 to 20 percent), low electrical conductivity (less than 0.3 dS/m), saturated water content between 45 to 47%, and a pH amounting to 7.5. Similar approaches can be used to allocate appropriate areas for the rehabilitation and protection of valuable native plant species.