Climate-Dependent Shifts in Vegetation Diversity and Composition Following Grazing Removal along an Aridity Gradient

Despite extensive studies, substantial uncertainties remain regarding the effects of grazing removal on vegetation dynamics, plant diversity and richness. We investigated aboveground vegetation responses to grazing exclusion across five different regions spanning arid (one region), semiarid (two regions), and humid (two regions) climates. In each region, vegetation was sampled using 4 m 2 plots equally distributed numbers between grazed and ungrazed areas. Vegetation composition was compared between regions and grazing treatment using dissimilarity analysis and non-metric multidimensional scaling (NMDS), while generalized linear mixed models (GLMMs) assessed differences in total vegetation cover, functional group cover, plant diversity and species richness between regions and between treatments. NMDS revealed significant differences in vegetation composition across regions and grazing treatments. Plant composition separation between grazed and exclosure plots was more pronounced in humid regions compared to the other regions. In the driest region, no significant differences were detected between grazed and ungrazed plots for any functional group nor for vegetation covers neither for species richness. In contrast, the most humid region showed increased mean cover percentages of perennials, grasses, and forbs under grazing removal. Plant diversity and evenness indices exhibited contrasting patterns after grazing exclusion, increasing in humid regions but decreasing in arid and semiarid regions. Overall, the magnitude of vegetation changes to grazing removal decreased with regional aridity. This study advances our understanding of how removal of intensive grazing in historically continuous ecosystems and climate interact shape grassland dynamics, highlighting the context-dependent effects of grazing removal on ecosystem functions under different climates.