Modeling the impact of rangeland management on forage production of sagebrush species in arid and semi-arid regions of Iran

Rangeland areas in the arid and semi-arid regions of Iran suffer from high grazing pressure and periodic droughts. These regions account for 85% of the national total rangeland area and make an important contribution to country's economy. To determine how to better manage this important resource, we developed a rangeland-livestock model using the Soil and Water Assessment Tool (SWAT). The model was tested in the river basin located in Tehran and Semnan Provinces of Iran. Sagebrush species of Artemisia sieberi Besser and Artemisia aucheri Boiss (covering more than 38% of the total rangeland areas in Hablehroud river basin) was chosen and some of their characteristics were used to add the necessary plant growth parameters to SWAT landuse database. In combination with the SWAT model, the Sequential Uncertainty Fitting Program (SUFI-2) was used to calibrate and validate the eco-hydrological model of the watershed based on river discharges and forage production of sagebrush species, taking into consideration historic grazing management. The model predicted well rivers discharges at eight hydrometric stations (P-factor 0.6–0.9; R-factor 0.85–1.5) as well as the sagebrush yield in three ecological zones across the basin. We found that the current grazing intensity was more than twice as much as the region's capacity. Based on some scenario analysis for water and grazing management we showed that through proper water management, we could obtain an average increase of about 40% in sagebrush forage production, while through grazing management an average increase of 30% could be obtained. This shows the region's nutritional capacity could substantially increase. The analytical framework used in this study could be applied to other arid and semi-arid environments for the assessment of forage production and livestock management to achieve a more sustainable food production.