Long-term active restoration of degraded grasslands enhances vegetation resilience by altering the soil seed bank

Long-term active restoration is often employed to restore degraded grasslands. The establishment of a viable soil seed bank is the key to successful restoration, as it enhances the resilience of vegetation. However, little is known of how the soil seed bank affects vegetation resilience following long-term active restoration of degraded grasslands. We determined seed abundance and species composition of the soil seed bank and soil properties and vegetation resilience of intact, degraded, and long-term (> 10 years) actively restored grasslands on the Tibetan plateau (3900-4200 m a.s.l.). The plant-soil-seed bank quality index and structural equation modelling (SEM) were used to assess the effect of the soil seed bank on vegetation resilience. After long-term (> 10 years) active restoration of degraded grasslands by sowing seeds of native plant species, the densities of transient and persistent seeds increased by 5%, but seed richness (number of species) decreased by 25% when compared with degraded grasslands. This occurred largely as a result of an increase in grass but decrease in forb seeds. Persistent seeds of grasses play an important role in the productivity of restored grasslands, while the density of persistent seeds serves as an indicator of the resilience of vegetation. A combination of the plant community and soil properties determined seed density. Here, we show for the first time that long-term active restoration enhances vegetation resilience of grasslands by altering the soil seed bank. A high seed density of sown Gramineae and a low seed density of forbs in the soil seed bank is a key to the successful active restoration of degraded grasslands.