4.2 Response of shrub species to stocking rate
With increasing duration of grazing history, the cumulative above-ground standing crop of shrubs and grasses increased under low stocking rates (CK, LG), while under high stocking rates (MG, HG) herbaceous plants gradually dominated the plant community. This is closely related to the palatability of grasses and the selective feeding habits of grazing livestock (Molyneux and Ralphs, 1992; Dulamsuren et al., 2008; Staver et al., 2009). Shrubs such as Artemisia frigida , Kochia prostrata , Caragana microphylla and Ceratoides latenshave good palatability in the desert steppe (Yan, 2019), and all are favored by sheep. Therefore, in desert steppe, which has sparse vegetation cover and relatively poor species composition (Han et al., 2007), shrubs are more likely to be consumed by sheep under high stocking rates, leading to their gradual disappearance in the plant community. In this study, the above-ground standing crop of shrubs decreased with increasing stocking rate, which is mainly due to the influence of Artemisia frigida . The change in Artemisia frigida was consistent with those reported by Kemp et al. (2018), who found a significant increase in Artemisia frigida under long-term non-grazing and light grazing in an Inner Mongolian desert steppe. Kemp et al. (2018) suggested that Artemisia frigida has good palatability, and that sheep preferentially consumed Artemisia frigida under high stocking rates. Wang et al. (2018) researched the population characteristics of Caragana microphylla across a stocking rate gradient in desert grassland and showed that the height and cover of Caragana microphylla decreased significantly with increasing stocking rate, which indicated that livestock consumption strongly inhibited the growth of Caragana microphylla . The height of shrubs gradually decreased with increasing stocking rate, while the quantitative characteristics of individuals (except for the height ofKochia prostrata , Caragana microphylla andCeratoides latens ) were highest under LG, indicating that light grazing can inhibit the apical dominance of shrubby plants (Christie et al., 2014).