Does restoration of degraded grasslands follow the theory of multiple stable states?

Grasslands on the Tibetan Plateau, notable for their high altitude, unique alpine climate, and significant contribution to global grassland areas, have undergone severe degradation driven by anthropogenic activities and climate change over recent decades. Various restoration strategies, including fencing, fertilizing, and reseeding, have been used to rehabilitate these degraded grasslands. Although multiple stable states have been identified during the degradation process caused by overgrazing, it remains largely unexplored how these states evolve throughout the restoration of degraded grasslands. By synthesizing 8392 data sets from 247 articles on restoration of vegetation, soil, and microbial communities in the Tibetan grasslands, we demonstrated that the restoration of degraded grasslands adheres to the theory of multiple stable states. As for specific indicators, restoration efforts resulted in a 330 % increase in the aboveground biomass of grasses, far surpassing that of legumes, sedges, and forbs. Restoration was more effective in semi-humid than semi-arid regions, with strong improvements in soil properties. Soil enzyme activities increased by 35 %–75 %. The ongoing trends of warming and wetting in the Tibetan Plateau are advantageous for grassland restoration. In lightly and moderately degraded grasslands, the restoration of soil properties to a healthy state occurred rapidly. However, restoration of heavily degraded grasslands, previously identified as beyond a ‘Point of No-Return’ state, required more time to break through the hysteresis, primarily due to slow soil recovery and the absent synergy between plants, soil and microorganisms. Consequently, distinct restoration strategies should be implemented for degraded grasslands based on the distinct initial degradation stages.