Effects of grazing on plant species and phylogenetic diversity in alpine grasslands, Northern Tibet

Plant diversity plays an important role in maintaining and upgrading ecosystem structure and functions, and there remain uncertainties on plant species and especially phylogenetic diversity to grazing in alpine grasslands. Therefore, this study compared the differences of plant species and phylogenetic alpha-and beta-diversity between grazing and fencing conditions at three alpine grasslands (ASMWG: alpine steppe meadow for winter grazing; ASMSG: alpine steppe meadow for summer grazing; AMSG: alpine meadow for summer grazing), Northern Tibet. At the ASMSG site, grazing significantly decreased mean nearest taxon distance (MNTD) by 19.33%, and increased Pielou by 7.06%. Plant community compositions between fencing and grazing conditions were different (p = 0.021) at the ASMSG site. However, the Pielou, MNTD and plant community composition were not significantly different between the fencing and grazing conditions at the ASMWG and AMSG site. Grazing significantly increased the niche overlap at the ASMWG (levins: 51.36%, schooner: 28.97%, pianka: 28.11%, Czech: 28.97%; morisita: 28.75%) and ASMSG site (schooner: 35.19%, petraitis: 4.63%, pianka: 26.45%, czech: 35.19%; morisita: 30.86%), indicating that grazing may increase plant species competition and competitive exclusion at the ASMWG and ASMSG site. In contrast, grazing did not significantly affect niche overlap at the AMSG site. Therefore, the response of plant diversity to grazing can be different between species and phylogenetic diversity, and among alpine grasslands.