Responses and feedback of the Tibetan Plateau’s alpine ecosystem to climate change

The Tibetan Plateau, also known as the "third pole of the Earth", houses a diverse array of alpine-ecosystem types and serves as a critical ecological security shield for China and even for many other regions of Asia. In recent decades, the rapid climate change in the Tibetan Plateau has led to profound changes in the structure and functioning of its ecosystem. Such changes in the ecosystem of the Tibetan Plateau can not only profoundly impact the environment of the high plateau itself but also extend significant influence over that of surrounding areas. With the continuous growth of data obtained via long-term in situ monitoring, manipulative experiments, satellite remote sensing, and model simulations, scientists have recently made significant advances in the research on the responses and feedback of the Tibetan Plateau's alpine ecosystem to climate change. Aiming to identify knowledge gaps and to stimulate future research, we provide a comprehensive review of past efforts to understand how climate change has impacted the Tibetan Plateau's alpine ecosystem, which in turn also provides feedback to the climate. In particular, we focus on the impacts of climate change on the structure and functioning of the ecosystem, including vegetation phenology, treeline position, species biodiversity, ecosystem productivity, and carbon sink, along with feedback involving vegetation changes to the regional climate and hydrology through local and teleconnected biophysical loops.A number of key findings emerge based on cumulative knowledge from old as wells as recent researches. (1) Climate warming during the past several decades has significantly advanced spring vegetation phenology in the Tibetan Plateau. (2) Further, warming has significantly shifted the treeline upward with varying amplitudes that may have been regulated by other factors such as precipitation and interspecific interactions. (3) The plant-community structure of the Tibetan Plateau's alpine steppe ecosystem is sensitive to climate change, with climate warming considerably reducing its biodiversity and species abundance. However, for the alpine-meadow ecosystem, the impact of climate warming on the diversity and species abundance is still inconclusive. (4) Furthermore, warming has significantly increased vegetation productivity, which can consequently lead to an enhanced carbon sink. Such warming-induced carbon accumulation by vegetation is higher in alpine meadows than in alpine steppes. However, the effect of climate change on soil carbon stock remains highly uncertain mainly because of the high spatial heterogeneity of soil properties and lack of information regarding deep-layer soil processes. (5) Warming-induced vegetation greening of the Tibetan Plateau provides an overall cooling effect countering the local warming and modulates the local and far-reaching precipitation patterns through teleconnected feedback to the East Asian monsoon. In particular, the modeling results suggest that this greening trend of the Tibetan Plateau increases precipitation in South China but reduces precipitation in the region between the Yellow and Yangtze Rivers.Even with the recent significant progress in the study on the ecosystem-climate interaction in the Tibetan Plateau, many knowledge gaps remain. These gaps provide opportunities for future research, which needs to expand and optimize long-term ecological observation networks to improve the understanding of key ecological processes and deepen the comprehension of the response and acclimation mechanisms of the alpine ecosystem under the influence of climate warming. The knowledge enhancement thus obtained will provide important guidelines for improving ecosystem management and safeguarding the ecological security in the Tibetan Plateau.