3.1 Vegetation characteristics
Species diversity is an important feature of ecosystem stability maintenance and function operation, and vegetation productivity is an important indicator to characterize the plant ecological function stability and regional ecological carrying capacity (Pennekamp et al., 2018; Campos-Herrera, et al., 2013). Tang et al. (2016) found that, with the succession of grassland to desert, species richness, total vegetation coverage, dominant abundance, richness index and aboveground organisms all showed a downward trend. In this study, compared with TS, the coverage, AGB, Shannon-Weiner index and richness decreased, which was similar to the results of the Meng et al. (2018) study. Due to the suitable water and heat conditions in the temperate steppe distribution area, it was mainly composed of perennial herbs. The Temperate Steppe Desert was used for water limitation, and part of the herbaceous plants were degraded and formed mainly herbaceous and semi-shrub vegetation. However, due to extremely rare rainfall, dwarf shrubs and subshrubs with strong drought resistance were mainly found in temperate desert (Zhang et al., 2015). Evolving from temperate steppe to temperate desert, the vegetation structure gradually becomes uniform and the stability of the ecosystem decreases (Sharma et al., 2009).