Global alpine ecosystems contain a large amount of carbon, which is sensitive to global change. Changes to alpine carbon sources and sinks have implications for carbon and climate feedback processes. To date, few studies have quantified the spatial-temporal variations in ecosystem carbon storage and its response to global change in the alpine regions of the Qinghai-Tibet Plateau (QTP). Ecosystem carbon storage in the northeastern QTP between 2001 and 2019 was simulated and systematically analyzed using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. Furthermore, the Hurst exponent was obtained and used as an input to perform an analysis of the future dynamic consistency of ecosystem carbon storage. Our study results demonstrated that: (1) regression between the normalized difference vegetation index (NDVI) and biomass (coefficient of determination (R-2) = 0.974, p < 0.001), and between NDVI and soil organic carbon density (SOCD) (R-2 = 0.810, p < 0.001) were valid; (2) the spatial distribution of ecosystem carbon storage decreased from the southeast to the northwest; (3) ecosystem carbon storage increased by 13.69% between 2001 and 2019, and the significant increases mainly occurred in the low-altitude regions; (4) climate and land use (LULC) changes caused increases in ecosystem carbon storage of 4.39 Tg C and 2.25 Tg C from 2001 to 2019, respectively; and (5) the future trend of ecosystem carbon storage in 92.73% of the study area shows high inconsistency but that in 7.27% was consistent. This study reveals that climate and LULC changes have positive effects on ecosystem carbon storage in the alpine regions of the QTP, which will provide valuable information for the formulation of eco-environmental policies and sustainable development.

Numerous studies have reported that treelines are moving to higher elevations and higher latitudes. Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing. Hence, climate change has been assumed to be the main driver behind this treeline movement. The latest review of treeline studies was published in 2009 by Harsch et al. Since then, a plethora of papers have been published studying local treeline migration. Here we bring together this knowledge through a review of 142 treeline related publications, including 477 study locations. We summarize the information known about factors limiting tree-growth at and near treelines. Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline. These conditions appear to have become favorable at many locations, particularly so in recent years. The review revealed that at 66% of these treeline sites forest cover had increased in elevational or latitudinal extent. The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements. Our analysis also revealed that while a greater percentage of elevational treelines are moving, the latitudinal treelines are capable of moving at greater horizontal speed. This can potentially have substantial impacts on ecosystem carbon storage. To conclude the review, we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced, increased or remain the same due to treeline migration. While the answer still remains under debate, we believe that all three hypotheses are likely to apply depending on the encroached ecosystem. Concerningly, evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future.