Abstract: Bare patch encroachment is linked with a shift in dominant plant species during the degradation of alpine meadows. Here, we investigated the dominant herbaceous species, and the occurrence of shrub invasion and bare patch cover during grassland degradation on 36 hillslopes along a watershed on the Qinghai-Tibetan Plateau. The increase in bare patch cover was treated as a measure of bare patch encroachment and examined in relation to shifts in dominant species. Based on the first two axes of principal coordinate analysis (PcoA1 and PcoA2), there were evident shifts in dominant herbaceous species. The PcoA1 axis represented a shift of dominant herbaceous species from K. pygmaea to Artemisia frigida and Ligularia virgaurea, while the PcoA2 axis represented a shift from K. pygmaea to Aster tataricus. Based on random forest and linear mixed models, both PcoA1 and PcoA2 were important predictors of bare patch encroachment. Furthermore, the structural equation model supported that the number of active pika burrows mediated the positive relationship between PcoA1 and bare patch cover, while the surface soil gravel cover mediated the relationship between PcoA2 and bare patch cover. These findings highlighted the ecological association between the shift of dominant species and bare patch encroachment, advancing previous findings by identifying the toxic species A. frigida, L. virgaurea and A. tataricus as biotic indicators and benefiting the management of the degrading alpine meadow hillslopes.

Key words: Bare patch, dominant shift, sedge and toxic plants, pika burrow, gravel mulch, alpine meadow hillslope