Is grazing exclusion effective in restoring vegetation in degraded alpine grasslands in Tibet, China?

TLDR

Overgrazing is a major driver of alpine grassland degradation in Tibet, and fencing has been widely used since 2004 to restore these ecosystems. The study investigates whether grazing exclusion effectively restores vegetation in degraded alpine grasslands. Researchers selected three alpine grassland types and compared plant community structure and biomass between fenced and freely grazed plots. Grazing exclusion raised vegetation cover, height, and aboveground biomass, yet biodiversity indices did not change, precipitation had a stronger effect, and the long‑term sustainability of these gains remains uncertain.

Abstract

Overgrazing is considered one of the key disturbance factors that results in alpine grassland degradation in Tibet. Grazing exclusion by fencing has been widely used as an approach to restore degraded grasslands in Tibet since 2004. Is the grazing exclusion management strategy effective for the vegetation restoration of degraded alpine grasslands? Three alpine grassland types were selected in Tibet to investigate the effect of grazing exclusion on plant community structure and biomass. Our results showed that species biodiversity indicators, including the Pielou evenness index, the Shannon–Wiener diversity index, and the Simpson dominance index, did not significantly change under grazing exclusion conditions. In contrast, the total vegetation cover, the mean vegetation height of the community, and the aboveground biomass were significantly higher in the grazing exclusion grasslands than in the free grazed grasslands. These results indicated that grazing exclusion is an effective measure for maintaining community stability and improving aboveground vegetation growth in alpine grasslands. However, the statistical analysis showed that the growing season precipitation (GSP) plays a more important role than grazing exclusion in which influence on vegetation in alpine grasslands. In addition, because the results of the present study come from short term (6–8 years) grazing exclusion, it is still uncertain whether these improvements will be continuable if grazing exclusion is continuously implemented. Therefore, the assessments of the ecological effects of the grazing exclusion management strategy on degraded alpine grasslands in Tibet still need long term continued research.