Study area
We selected two regions along the precipitation gradient in northeastern Iran in the Khorassan-Kopet Dagh floristic province of the Irano-Turanian region, located between 35°43’-36°44’N and 58°40’−60°27’ E. Based on the meteorological data, Khaje has a dry climate and Baharkish has a semi-arid climate, expressed by de Martonne aridity index (see Table 1 for more details). The mean annual precipitation (20-year mean) is 255 mm in Khaje and 385 in Baharkish. A steppe vegetation with the dominant A. kopetdaghensis Krasch.M.Pop. & Linecz ex Poljak prevails in both of these areas. This species is a semi-shrub from the Asteraceaefamily, native to northeastern Iran and dominant throughout much of this region. Artemisia species have been documented to facilitate common annual and perennial forbs in this region (Reisner et al., 2015) by creating favorable suitable microsites, reducing evapotranspiration (e.g., Holthuijzen & Veblen, 2015), mediating soil temperatures (Davies et al., 2007), raising soil water content via hydraulic lift (e.g., Holthuijzen & Veblen, 2015) and accumulating soil nutrients (Cardon et al., 2013).