Resilience of revegetated grassland for restoring severely degraded alpine meadows is driven by plant and soil quality along recovery time: A case study from the Three-river Headwater Area of Qinghai-Tibetan Plateau

Resilience is crucial to promote the ecosystem sustainability and maintain ecosystem functions and services. Clarifying the variation regularity of the resilience can provide a theory foundation for the restoration and management of degraded ecosystems. Grassland cultivation has been largely used to restore extensively distributed Black Beach, the severely degraded alpine meadow on the Qinghai-Tibetan Plateau (QTP). However, few researchers have documented the resilience of the revegetated grasslands along the succession gradients. In this study, we surveyed the revegetated grasslands on the QTP at different restoration times: 4-year, 6-year, 9-year, 12-year, 13-year, 14-year, 16-year, 18-year by using chronosequence approach to identify the resilience of the revegetated grasslands from the perspectives of plant and soil quality. We treated Black Beach as the baseline for restoration, and non-degraded healthy alpine meadow as the target for the restoration. We used the MDS method to identify the appropriate indicators and created an integrated assessment system that quantified the resilience of plant, soil, plant-soil system of the revegetated grasslands at different recovery years. The results showed that the non-linear resilience of revegetated grasslands were identified for the plant, soil and plant-soil systems along the temporal gradients. The plant resilience of the revegetated grasslands peaked at the 12th recovery year. The soil of the revegetated grasslands was superior to severely degraded grasslands after 13 years of revegetation. Asynchrony existed between the resilience of soil and that of the plant along the temporal gradients. The plant-soil system resilience of the revegetated grasslands peaked at the 16th recovery year. From the perspectives of plant, soil, plant-soil system, the recovery time of severely degraded grassland should be at least 16-18 years to reach a relative stable state. Revegetated grassland can be used as an effective restoration approach to improve the quality and resilience of plant and soil in the severely degraded alpine meadow on the QTP.