An assessment of nonequilibrium rangeland dynamics was conducted in the Aru basin, a semiarid site located in the very dry northwest part of the Chang Tang Nature Reserve, Tibet, China. A grazing gradient approach was used to examine the effects of different livestock grazing intensities on vegetation, providing data to determine if plant–herbivore interaction has been a major structuring force of the plant community and thus to indicate what type of dynamic might apply in the study area. No significant differences were found between a highly grazed site and a lightly grazed site in vegetation cover, standing biomass, and Shannon–Wiener species diversity index of total, graminoid, forb, and tomtza (Oxytropis glacialis Benth. ex Bunge) functional groups, with the exception that tomtza coverage was significantly higher at the highly grazed (1.04%) than at the lightly grazed site (0.02%). Grazing intensity alone did not explain a significant amount of variation in the plant species data. These results indicate that a dominance of nonequilibrium dynamics appears to be the case in the basin, probably one of the least-arid sites in the northwest Chang Tang region of the Tibetan Plateau. Thus, opportunistic livestock management strategies adapted to variable vegetation production from year to year, rather than the setting of a rigid stocking rate that assumes a stable carrying capacity, is probably the most plausible approach for managing livestock and its relationship to biodiversity values in this region.
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Vol. 63 • No. 4