Effect of grazing management strategies on alpine grassland on the northeastern Qinghai-Tibet Plateau

In recent decades, alpine grassland has been seriously degraded owing to overgrazing across the Qinghai Tibetan Plateau (QTP), although grazing exclusion has been widely adopted to restore degraded QTP grassland. It remains unknown whether such management approach is effective for all degraded alpine grasslands, and the effect of different grazing management strategies on grassland at varying levels of degradation needs to be assessed. In this study, plots with three grazing management treatments (free grazing, FG; reduced grazing, RG; grazing exclusion, GE) and four degradation stages (non-degradation, ND; light degradation, LD; moderate degradation, MD; heavy degradation, HD) were compared. Our results showed that the total aboveground biomass (AGB) and species richness (SR) under free grazing treatment were reduced with increasing degradation, whereas total belowground biomass (BGB) under free grazing treatment increased with increasing degradation. Furthermore, the responses of SR, AGB and BGB to grazing management varied with the degree of degradation. The total AGB in the LD, MD and HD stages increased significantly following RG and GE treatments, but there was no significant change of AGB in the ND stage. Meanwhile, SR reduced significantly following RG and GE treatments under all degradation stages except for HD. After RG and GE treatments, the total BGB increased significantly in the ND stage but decreased significantly under GE treatment in the MD and HD stages. Furthermore, the responses of plant functional groups to grazing management were varied. The Gramineae AGB increased significantly across all degradation levels under RG and GE treatments, whereas the sedges AGB decreased (except in the MD stage under GE management). Our results suggested that the effect of grazing management on alpine grassland depended on the degree of degradation.