Uncovering the multi-fencing effects: Changes in plant diversity across dimensions and spatio, and the relationship between diversity and stability.

Plant diversity is fundamental to maintaining grassland ecosystem function. Rangeland managers use fencing as a strategy to enhance plant diversity in degraded grasslands. However, the effects of this natural management approach on grasslands across a wide range of environmental gradients and its spatial pattern remain unclear. This study investigated 37 pairs of fencing and grazing sites along an 1800 km transect of alpine grasslands on the Tibetan Plateau to evaluate the effects of fencing on plant species, functional, and phylogenetic alpha and beta diversity. Fencing increased plant functional and species alpha-diversity, as well as phylogenetic and functional beta-diversity by 0.20%-26.18%, but decreased species beta-diversity by 0.70%. The sensitivity of functional diversity to fencing was higher in alpine meadows than in alpine steppes and alpine desert steppes. Fencing resulted in spatial heterogeneity in plant alpha and beta diversity in alpine grasslands. The beta-diversity of plant communities in the three dimensions across all the alpine grasslands was dominated by turnover components. The response of plant diversity to fencing increased with longitude but declined with latitude and elevation. Consequently, the effects of fencing on plant diversity in Tibetan alpine grasslands are associated with grassland types and climatic conditions. Notably, fencing did not consistently yield positive outcomes for plant diversity, indicating it should be applied selectively for biodiversity restoration. Given the nonlinear relationship between diversity and ecosystem stability, it is recommended that restoration of degraded grasslands should consider not only species selection but also a balanced composition of species with varied functional and phylogenetic traits.