Arid and semi-arid vegetation is characterized by plant patches of different sizes, and plant cover is determined by patch size (PS) and number of patches (NP). However, it is still unclear how PS and NP contribute to the restoration of degraded grasslands through grazing exclusion (GE). Transect lines were sampled in six alpine steppe communities in Tibet in 2017 and 2018. Both PS and NP were assessed and compared between inside and outside grazing exclosures. Our results showed that grazing exclosures increased the mean size but decreased the total number of plant patches. This pattern of change was common to other species and could not be attributed to a shift in community composition. The results suggest that the recovery of the degraded alpine steppe is being driven by PS at the expense of NP. By promoting the expansion of the larger patches while excluding the smaller ones, GE led to an aggregating pattern with a higher proportion of bare ground, potentially reducing primary productivity.

The impacts of human-driven environmental changes on the stability of natural grasslands have been assessed by comparing differences between manipulative warming and grazing plots and reference plots. However, little is known about whether or how ambient climate regulates the effects of manipulative treatments. A 36-year observational dataset shows that there is a nonlinear response of community stability to ambient climate. Manipulative warming and grazing decrease community stability with experiment duration through an increase in legume coverage and/or decrease in species asynchrony, due to exceeding the threshold of background annual mean air temperature with decreasing background annual mean air temperature through time during the 10-year experiment period. Moreover, the temperature sensitivity of community stability is more sensitive under the ambient treatment than under the manipulative treatments. Therefore, our study emphasizes the importance of the context dependency of the response of community stability to human-driven environmental changes.