When did the world’s largest alpine meadow ecosystem originate? How has it responded to climate changes across timescales? How will it change under future global warming? These are fundamental theoretical questions critical for tackling climate change and conserving the fragile alpine ecosystem. A new study published in Nature Ecology & Evolution provided key insights into these issues.

Led by Prof. ZHAO Yan from the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, researchers analyzed 5,000 fossil pollen samples extracted from two long lake-sediment cores of the Zoige Basin (~3400 m a.s.l.), eastern Tibetan Plateau. By integrating biomization, numerical analysis, statistical modelling, and vegetation simulations, they revealed a detailed picture of vegetation dynamics across timescales since 3.5 million years ago (Ma). 

These lines of evidence show that vegetation underwent transformations from stable forest in the mid-late Pliocene Period (3.5–2.73 Ma) to co-dominance of forest and steppe in the early Quaternary Period (2.73–1.54 Ma) and to a meadow-dominated ecosystem after ~1.54 Ma. On orbital timescales, forest and grassland successions exhibited distinct 20-, 40-, and 100-kyr cycles, co-driven by low-latitude summer insolation and high-latitude ice volume changes.

However, the influence of ice volume showed phased amplification over time. On millennial timescales, frequent shifts in vegetation types occurred since ~1.5 Ma, primarily modulated by high-latitude ice sheet dynamics. Vegetation dynamics on various timescales were closely linked to global temperature changes, and a past global warming of ~2-3 °C relative to pre-industrial levels was the most important threshold for forest expansion and meadow resilience loss on the Tibetan Plateau. 

This study establishes the longest and most continuous pollen record with consistent resolution globally. It provides the first evidence that the meadow-dominated ecosystem on the eastern Tibetan Plateau became established around 1.5 Ma. This major ecological transition was forced by combined effects of global cooling and monsoon evolution. 

The findings on vegetation resilience and climate threshold effects offer vital insights for predicting how vegetation will respond to future global warming. They also highlight a critical risk: a global warming exceeding 2 °C relative to pre-industrial values would likely trigger a major transformation of modern alpine meadow ecosystem.

Reference: Zhao, Y., Qin, F., Cui, Q. Y., et al. Three-and-a-half million years of Tibetan Plateau vegetation dynamics in response to climate change. Nature Ecology Evolution (2025). https://doi.org/10.1038/s41559-025-02743-2.

Changes in the resilience of major vegetation types (a) and their relationships with global temperature and atmospheric CO₂ concentrations (b) (Image by ZHAO Yan)