Grasslands occupy nearly three quarters of the land surface of the Qinghai-Tibet plateau (QTP) and play a critical role in regulating the ecological functions of the QTP. Ongoing climate change and human interference have greatly affected grasslands on the QTP. Differentiating human-induced and climate-driven vegetation changes is vital for both ecological understanding and the management of husbandry. In this study, we employed statistical analysis of annual records, various sources of remote sensing data, and an ecosystem process model to calculate the relative contribution of climate and human activities to vegetation vigor on the QTP. The temperature, precipitation and the intensity and spatial pattern of livestock grazing differed between the periods prior to and after the year 2000, which led to different vegetation dynamics. Overall, increased temperature and enhanced precipitation favored vegetation growth. However, their combined effects exhibited strong spatial heterogeneity. Specifically, increased temperature restrained vegetation growth in dry steppe regions during a period of slightly increasing precipitation from 1986 to 2000 and in meadow regions during a period of precipitation decline during 2000–2011, thereby making precipitation a dominant factor. An increase in precipitation tended to enhance vegetation growth in wet meadow regions during warm periods, and temperature was the limiting factor in Tibet during dry periods. The dominant role played by climate and human activities differed with location and targeted time period. Areas dominated by human activities are much smaller than those dominated by climate. The effects of grazing on grassland pasture were more obvious under unfavorable climate conditions than under suitable ones.

Warming-induced carbon loss through terrestrial ecosystem respiration (Re) is likely getting stronger in high latitudes and cold regions because of the more rapid warming and higher temperature sensitivity of Re (Q₁₀). However, it is not known whether the spatial relationship between Q₁₀ and temperature also holds temporally under a future warmer climate. Here, we analyzed apparent Q₁₀ values derived from multiyear observations at 74 FLUXNET sites spanning diverse climates and biomes. We found warming-induced decline in Q₁₀ is stronger at colder regions than other locations, which is consistent with a meta-analysis of 54 field warming experiments across the globe. We predict future warming will shrink the global variability of Q₁₀ values to an average of 1.44 across the globe under a high emission trajectory (RCP 8.5) by the end of the century. Therefore, warming-induced carbon loss may be less than previously assumed because of Q₁₀ homogenization in a warming world.

Measurements of Volatile Organic Compounds (VOC) are analyzed to characterize the sources impacting the Hong Kong area. The ratios of different VOC species, m,p-xylenes-to-ethylbenzene, C₆H₁₄-to-toluene and p-xylene-to-total xylenes are used for diagnostic analyses. Photochemical age analysis shows that the sources of reactive aromatics, the most important contributor to the photochemical reactivity, do not appear to be preferentially located in downtown Hong Kong. In addition, they do not appear to be dominated by mobile emissions based on the analyses of speciated VOC data from an earlier study, but related to industrial, waterfront, and fuel-storage activities. The ratios, p-xylene-to-total xylenes and dSO₂/dNO_y, suggest that the anomalously high pollutant concentrations in western Hong Kong in the early morning hours of two episode days appear to have come from transport of urban-type emissions. Comparison of observed ambient ratios of selected VOC and their ratios in the speciated VOC emission inventories for Hong Kong and adjacent Pearl River Delta (PRD) Region gives mixed results. The observed ratio C₆H₁₄-to-toluene is consistent with the speciated version of the VOC emission inventory. The ratios of selected alkanes are not. This may be caused by the inaccuracies in the inventory and/or the speciation method.

The northern Tibetan Plateau is the most traditional and important semi-nomadic region in Tibet. The alpine vegetation is sensitive and vulnerable to climate change and human activities, and is also important as an ecological security in protecting the headwaters of major rivers in Asia. Therefore, the Tibetan alpine grasslands have fundamental significance to both Mainland China and South Asia. The pasture degradation, however, likely threatens the livelihood of residents and the habitats of wildlife on this plateau. Since 2004, the government has launched a series of ecological restoration projects and economic compensatory payment polices. Many fences were additionally built on degraded pastures to prevent new degradation, to promote functionality recovery, and to balance the stocking rate with forage productivity. The grazed vs. fenced paired pastures across different zonal grassland communities along evident environmental gradients provide us with a natural comparative experiment platform to test the relative contributions of natural and anthropogenic factors. This study critically reviews the background, significance of and debates on short-term grazing exclusion with fences in this region. We also aim to figure out scientific and standardized workflows for assessing the effectiveness of grazing exclusion and compensatory payments in the future.

Alpine grasslands on the Tibetan Plateau are claimed to be sensitive and vulnerable to climate change and human disturbance. The mechanism, direction and magnitude of climatic and anthropogenic influences on net primary productivity (NPP) of various alpine pastures remain under debate. Here, we simulated the potential productivity (with only climate variables being considered as drivers; NPP_P) and actual productivity (based on remote sensing dataset including both climate and anthropogenic drivers; NPP_A) from 1993 to 2011. We denoted the difference between NPP_P and NPP_A as NPP_pc to quantify how much forage can be potentially consumed by livestock. The actually consumed productivity (NPP_ac) by livestock were estimated based on meat production and daily forage consumption per standardized sheep unit. We hypothesized that the gap between NPP_pc and NPP_ac (NPP_gap) indicates the direction of vegetation dynamics, restoration or degradation. Our results show that growing season precipitation rather than temperature significantly relates with NPP_gap, although warming was significant for the entire study region while precipitation only significantly increased in the northeastern places. On the Northern Tibetan Plateau, 69.05% of available alpine pastures showed a restoration trend with positive NPP_gap, and for 58.74% of alpine pastures, stocking rate is suggested to increase in the future because of the positive mean NPP_gap and its increasing trend. This study provides a potential framework for regionally regulating grazing management with aims to restore the degraded pastures and sustainable management of the healthy pastures on the Tibetan Plateau.