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The changes in vegetation composition and plant diversity of three different alpine ecosystems: alpine meadow, alpine steppe and alpine desert, impacted by different levels of degradation (healthy, lightly degraded and moderately degraded) were examined across a large-scale transect on the Qinghai-Tibet Plateau. The alpine meadow was dominated by sedges, the alpine steppe was dominated by grasses and the alpine desert was dominated by shrubs. The alpine meadow had the highest species diversity, whereas the alpine steppe had the lowest and tended to be dominated by a few species. Forbs were the dominant and most diverse functional group in the alpine meadow and the alpine steppe, which was different from the alpine desert. The importance values of the dominant species and levels of diversity measured by various vegetation indices were only slightly different in the degraded sites as compared with the non-degraded alpine meadow and steppe, whereas the alpine desert showed large changes in the composition and diversity of the plant community in response to degradation. In conclusion, the plant composition of the alpine meadow and alpine steppe ecosystems was more stable and appeared more resistant to disturbance than that of the alpine desert ecosystem.