How does grazing exclusion influence plant productivity and community structure in alpine grasslands of the Qinghai-Tibetan Plateau?

Abstract

Grazing exclusion by fencing is a commonly used management practice for restoring the degraded alpine grasslands on the Qinghai-Tibetan Plateau (QTP). However, there is currently no consensus on how grazing exclusion influences plant productivity and community structure in alpine grasslands in this region. Here, a meta-analysis was conducted to quantitatively assess the impacts of grazing exclusion on plant biomass (aboveground biomass, AGB; belowground biomass, BGB; and total biomass, TB) and various plant diversity indices (species richness, Shannon-Wiener diversity index, and Pielou evenness index) in alpine grasslands on the QTP. The results showed that on average, grazing exclusion significantly increased plant coverage, AGB, BGB, TB, and species richness by 34.4%, 93.1%, 58.0%, 67.4%, and 8.3%, respectively. In contrast, significant reductions in both Shannon-Wiener diversity index (−6.7%) and Pielou evenness index (−6.1%) were detected following grazing exclusion. It was observed that the effectiveness of grazing exclusion on recovering plant coverage, AGB, TB, and species richness decreased with the duration of grazing exclusion, and the effect size of plant species richness was negatively correlated to the duration of grazing exclusion. These results indicated that plant species might decrease with the duration of grazing exclusion. The increases in AGB, BGB, and TB were all significantly higher in alpine meadow than those in alpine steppe and alpine desert steppe, demonstrating that grazing exclusion was more effective in promoting plant productivity in alpine meadow than in the other two grassland types. However, the effects of grazing exclusion on plant diversity indices did not differ significantly among the three grassland types. The research suggest that grazing exclusion is an effective way to recover plant productivity and diversity in alpine grassland of the QTP, especially in alpine meadow, and the period of grazing exclusion should be related to the state and function of the grassland.