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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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Spatiotemporal dynamics of aboveground biomass (AGB) is a fundamental problem for grassland environmental management on the Qinghai-Tibet Plateau (QTP). Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data can feasibly be used to estimate AGB at large scales, and their precise validation is necessary to utilize them effectively. In our study, the clip-harvest method was used at 64 plots in QTP grasslands to obtain actual AGB values, and a handheld hyperspectral spectrometer was used to calculate field-measured NDVI to validate MODIS NDVI. Based on the models between NDVI and AGB, AGB dynamics trends during 2000–2012 were analyzed. The results showed that the AGB in QTP grasslands increased during the study period, with 70% of the grasslands undergoing increases mainly in the Qinghai Province. Also, the meadow showed a larger increasing trend than steppe. Future AGB dynamic trends were also investigated using a combined analysis of the slope values and the Hurst exponent. The results showed high sustainability of AGB dynamics trends after the study period. Predictions indicate 60% of the steppe and meadow grasslands would continue to increase in AGB, while 25% of the grasslands would remain in degradation, with most of them distributing in Tibet.

This paper evaluated changes in vegetation from 2000 to 2012, based on 1-km resolution 16-day composite Moderate Resolution Imaging Spectroradiometer (MODIS) Normalised Difference Vegetation Index (NDVI), and related them to changes in estimates of human disturbance on the rangelands of the Qinghai-Tibet Plateau. The main rangeland types studied were desert, steppe and meadow with the latter mainly found in the southern and eastern parts of the study area. The results indicated that human disturbance was distributed mainly in the southern and eastern parts of the study area and corresponded with high NDVI values. The NDVI values showed an upward trend over the study period, with 28.5% of the study area exhibiting a significant increase. The proportion of rangelands that experienced a downward trend in NDVI increased as the level of human disturbance increased. Of the different rangeland types, meadow had the highest NDVI values, the greatest human disturbance, and the highest proportion of rangelands that exhibited a significant decrease in NDVI. Compared with areas with no human disturbance, meadow and steppe rangelands that experienced an increase in human disturbance had lower rates of increase in their NDVI values but, conversely, desert rangelands showed the opposite trend. In addition, it was found that precipitation had the dominant influence on NDVI values and that higher precipitation and slighter lower temperatures over the period of the study were related to an increase in NDVI values.