Successional trajectories of herbaceous functional groups induced by grazing exclusion in the desert of the western Inner Mongolia plateau

Grazing-induced grassland degradation has attracted increasing attention worldwide, with arid desert regions being particularly affected due to their low precipitation and fragile ecosystems. The vegetation degradation caused by grazing in these regions is especially severe. Grazing exclusion has been widely implemented as a management strategy to rehabilitate degraded grasslands; however, its effects on the successional recovery of desert vegetation, particularly herbaceous species, remain insufficiently understood. In this study, we conducted a grazing exclusion experiment in the desert region of western Inner Mongolia, monitoring continuously from 2022 to 2024, to examine the effects of short-term (1–3 years) and medium-term (6–9 years) grazing exclusion on the biodiversity and biomass of herbaceous plants. In addition, we evaluated changes among different plant functional groups (i.e., perennial tall grass, perennial short grass, perennial forb and annual-biennial plant). The main findings of this study were as follows: (1) With increasing period of grazing exclusion, the alpha diversity of herbaceous plant communities first decreased but then increased. Grazing exclusion resulted in a more even distribution of species without altering total species richness. (2) Grazing exclusion promoted an increase in aboveground biomass, although biomass fluctuated across years because of the influences of annual and biennial species. (3) As the duration of exclusion increased, the proportion of perennial species, especially perennial grasses, increased. Notably, perennial tall grasses were observed only in plots that had been excluded from grazing for more than 6 years. Grazing exclusion, in conjunction with climatic factors, serves as the primary driver of the succession of dominant herbaceous plant species, promoting a transition from annual and biennial species to short perennial grasses and eventually to tall perennial grasses. The presence of tall perennial grasses contributed to the relative stability of the plant community under changing environmental conditions. This study enhances our understanding of the response of desert vegetation to grazing exclusion and provides insights into the successional processes that occur in arid grasslands.