• Energy Research

The world's largest alpine pastures are found on the Tibetan Plateau, where considerable climate changes and human impacts have been experienced. Identifying their contributions to terrestrial productivity is essential if we are to adapt to, or mitigate the effects of, climate change. In this work, we begin by showing how the current warming and wetting of the climate over the last three decades has favored plant growth, as consistently captured by satellite observations and 15 models. However, the interactions between climate factors explain less of the variation in greenness observed by satellites after the 2000s, implying non-climatic influences. Next, we show that there is a significant negative impact of livestock grazing on pasture greenness, especially in peak summer. Official statistics across 72 counties verify these negative impacts, especially in poorer pastures with a higher density of grazing livestock. The variation in grazing density has a stronger negative effect on vegetation growth during the early part of the growing season after the 2000s, as compared with that before the 2000s. We found a compensatory effect of grazing and climate on alpine grassland growth, and the grazing regulates the response of vegetation greenness to climate change by modulating the dependency of vegetation growth on temperature. Thus, we suggest there is a weakening influence of climate on the greenness of alpine pastures, largely due to a strengthening influence of management, which should be considered by both the scientific community and policymakers.

SignificanceCold regions contain vast stores of permafrost carbon. Rapid warming will cause permafrost to thaw and plant respiration to accelerate, with a resultant loss of CO2, but could also increase the fixation of CO2by plants. A network of 32 eddy covariance sites on the Tibetan Plateau, which has the largest store of alpine permafrost carbon on Earth, shows that this region functions as a net CO2sink. Our sensitivity analyses, experiments, and model simulations consistently showed that the fixation of CO2by plants outpaces the loss of CO2from permafrost and accelerates plant respiration. This indicates a plant-dominated CO2balance on the Tibetan Plateau, which could provide a negative feedback to climate warming.