2.1 Site Description
The study was conducted in Alxa League, the westernmost part of the Inner Mongolia Autonomous Region. It is located at 37°24′ ~ 42°47′N, 97°10′ ~ 106°53′E. The area is dominated by high plains, with large desert and Gobi areas, followed by grassland areas, and smaller mountain, forest, and arable areas. It has an altitude range of 820 ~ 1 400 m. The region has an arid climate and strong winds, and is a typical arid desert area. The average annual temperature is about 8.3 ℃, the average annual precipitation is 40-180 mm, mainly in July and August, and the average annual evaporation is 2,400-4,200 mm. Soil types have obvious zonal characteristics, from northwest to southeast, gray-brown desert soil, gray-desert soil and gray-calcium soil are distributed in order, and in the lake basin area there are saline soils. The vegetation types are mainly desert vegetation, oasis vegetation and mountain vegetation. Natural poplar forests grow in the Ejin Oasis area, while the presence of the Helan Mountains enriches the biodiversity and complexity of the Alxa Plateau system. Alxa region is an ecologically fragile area, which is one of the birthplaces of sandstorms in China. In recent years, around the three major deserts, a large area of artificial afforestation has been carried out, and artificial H. ammodendron plantations have become an important artificial barrier to curb land desertification and promote ecological restoration in the region. Fig. 1 shows the geographical location and experimental survey area of Alxa.