Effects of Microclimate and Moderate Grazing on the Characteristics of Alpine Meadow Plant Community

Grazing is the dominant use of alpine grasslands on the Qinghai-Tibet Plateau. However, controlled field experimental studies to understand the processes and mechanisms underlying the effects of grazing on the alpine meadow grasslands of the central Qinghai-Tibetan Plateau have rarely been conducted. This study used 11 years of data from an ongoing field experiment that has been strictly controlling the location (fixed 8 m grazing plots), period (fixed grazing duration, that is, 3 days at a time for 7 h per day and 3 times a year), and quantity (one adult yak per plot at a time) of grazing on alpine meadow grassland in the Namtso region of the central Qinghai-Tibetan Plateau, to understand the effects of grazing on alpine meadow grasslands. Our results show that moderate grazing significantly increased the coverage of Kobresia pygmaea dominated sedges by 7.8% and that of Potentilla fruticose dominated shrubs by 35%, while moderate grazing significantly decreased the coverage of grasses by 69% in alpine meadows. Further, moderate grazing significantly decreased the Simpson diversity index by 8.8% and increased the dominance of the plant community by 15.13%. Furthermore, moderate grazing decreased the Simpson diversity index in normal and dry years (P < 0.01), whereas moderate grazing increased dominance in dry years (P < 0.01). Grazing increased sedge coverage in normal and dry years (P < 0.05) and shrub coverage in the dry years (P < 0.05). Overall, 1) moderate grazing maintained and promoted the alpine meadow, which is dominated by K. pygmaea. 2) Long-term grazing prohibitions (that is, periods without grazing) in the alpine meadows increased the convergence of grasses and potentially led to the transformation of the alpine meadow to alpine steppe. 3) Soil moisture regulated the effects of grazing on the characteristics of plant communities in alpine meadows.