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Overgrazing and climate warming may be important drivers of alpine rangeland degradation in the Qinghai-Tibetan Plateau (QTP). In this study, the effects of grazing and experimental warming on the vegetation of cultivated grasslands, alpine steppe and alpine meadows on the QTP were investigated. The three treatments were a control, a warming treatment and a grazing treatment and were replicated three times on each vegetation type. The warming treatment was applied using fibreglass open-top chambers and the grazing treatment was continuous grazing by yaks at a moderately high stocking rate. Both grazing and warming negatively affected vegetation cover. Grazing reduced vegetation height while warming increased vegetation height. Grazing increased but warming reduced plant diversity. Grazing decreased and warming increased the aboveground plant biomass. Grazing increased the preferred forage species in native rangelands (alpine steppe and alpine meadow), while warming increased the preferred forage species in the cultivated grassland. Grazing reduced the vegetation living state (VLS) of all three alpine grasslands by nearly 70%, while warming reduced the VLS of the cultivated grassland and the alpine steppe by 32% and 56%, respectively, and promoted the VLS of the alpine meadow by 20.5%. It was concluded that overgrazing was the main driver of change to the alpine grassland vegetation on the QTP. The findings suggest that grazing regimes should be adapted in order for them to be sustainable in a warmer future.

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Using plant community analysis methods, we analyzed the floristic characteristics, species composition, community structure, population structure, and spatial distribution patterns of a Betula dahurica forest on the "1238" mountain of Badaling in Beijing, China. The results show that: 1) There are 33 plant species in the B. dahurica community, including 18 woody plant species. The B. dahurica forest is a monodominant community with 75.9% dominance. 2) Based on diameter at breast height (DBH) size class distribution, the population structure of B. dahurica and Acer mono-two heliophyllous and pioneer tree species-is cascade-type, with both in an increasing stage. The population structure of Tilia mandshurica and T. mongolica, two shade-tolerant tree species, is inverse-J type, and they have more young seedling individuals and regenerate more stably. They are associated species of the pioneer tree species. The population structure of Quercus mongolica, as the associated species of climax species in the community, is sporadic, and its regeneration is fluctuating and random. Fraxinus rhynchophylla is a shade-tolerant tree species which has a unibar population structure and climax characteristics of pioneer tree species. The relative frequency of young seedlings reached 0.4. 3) The dominant species B. dahurica is still in an increasing stage, and the regeneration of other species is steady or partly influences the community, putting the community in the pioneer species stage. From the population structure and distribution frequency of F. rhynchophylla, the B. dahurica forest will approach to a climax state in the future.