Tragacanth Astragalus species are the dominant species of many mountains of Iran, and besides producing tragacanth gum, they play a major role in providing ecosystem services by controlling and influencing atmospheric precipitations. On the other hand, the correlation of these rangeland ecosystems with arid and semi-arid climates has made them vulnerable to climate change.The two species Astragalus verus and Astragalus gossypinus are the most productive species of flake and ribbon tragcanth gum, respectively. In the present study, on a regional scale, the climatic ecological niche of the above two species, the map of tragacanth gum production and the economic value of it, in central Zagros (with 2 million hectares area) are mapped for current and future climate changes (year 2050) using Chelsa (CanESM2 General Circulation Model) bioclim data. For this purpose, a total of 1053 geographic coordinates of the occurrence points of two species were recorded and the most important bioclim variables affecting the distribution of species include: BiO1 average annual temperature, BiO2 average daily temperature range, BiO7 annual temperature range and BiO12 annual precipitation, were used to map species distribution, using models SRE, Maxent, RF, GBM, GLM and ANN in biomod2 package. The eva‎luation of the models using the AUC index showed that the RF model have the best performance for predicting the habitat map of A. verus and A. gossypinus, respectively(AUC=0.988 and 0.971). The area of habitat or climatic ecological niche of two species was estimated to be 1,188,121 and 566,849 hectares, respectively. A map of the gum production of two species was made using canopy point data, gum production data and bioclim data, using non-linear regression(GAM). The amount of flake and ribbon gum production was 6120 and 270 tons, respectively, and the current value of this ecosystem service based on market price was calculated as 101.530 and 8.564 billion dollars, respectively.The prediction of the species distribution map under climate change conditions using the RCP26 scenario for the A. verus and A. gossypinus indicates a decrease of 67% and 53% until 2050, respectively. In this way, due to climate change, the production of flake and ribbon gum will decrease to 2550 and 164 tons, causing a total loss of 62.588 billion dollars. On a local scale(Shour River watershed), a map of runoff yield under the current and future conditions of climate change was produced using the bioclim data of the Chelsa with an area of 150 thousand hectares in TerrSet software, and the excess runoff damage was valuated by the replacement cost method.The results showed that the amount of runoff yield will reach 105 million cubic meters from the current 70 million cubic meters, under the RCP26 scenario of 2050. Preventing the damage of excess runoff, it is necessary to carry out various watershed operations with a credit amounting to 660 billion Rials based on the present value. This study proved the integration possibility of SDM methods in biomod2 and TerrSet to create a map of provisioning and regulating ecosystem services under climate changes or land use changes and with the purpose of valuation. Due to the importance, extent and considerable economic value of tragacanth rangelands in providing all kinds of ecosystem services, the protection and proper exploitation of these habitats should be on the main agenda of managers and users of natural resources. In addition , in order to deal with natural threats such as floods or droughts under climate change conditions, preparing a runoff yield map for studying and implementing watershed management plans, becomes more important.

عليرضا موسوي , مصطفي تركش اصفهاني

سعيد سلطاني كوپائي

حميدرضا كريم زاده , عليرضا علي پور , مرتضي خداقلي