Application of SWAT to model forage production of Sagebrush rangelands in steppe and semi-steppe regions of Iran

Sagebrush rangelands in Iran with 39.71 million hectares include more than 46% of the total rangelands, and are recognized as an important and dominant rangeland species in Iran Turan flora. These lands are often associated with grazing of livestock and wildlife. To determine how to better manage this important resource, a rangeland-livestock model was tested in the Hablerud river basin located in Tehran and Semnan Provinces of Iran using the Soil and Water Assessment Tool (SWAT). With regard to climate variation, this watershed consists of three ecological zones: semi-steppe, steppe, and desert. Calibration and validation of model were tested with the Sequential Uncertainty Fitting Program (SUFI-2). Results showed that observed data of forage production were inside or quite close to the predicted bands in three zones. Also, based on the model results, simulated forage production varied from 0.35 to 0.5, 0.15 to 0.26, and 0.033 and 0.1 ton ha-1 in semi-steppe, steppe, and desert, respectively. Sensitive analysis showed that whatever we move from semi steppe to desert, the number of sensitive parameters increases and water and soil parameters becomes more sensitive in forage production.