When did the world's largest alpine meadow ecosystem originate? How has it responded to climate changes over different timescales? These questions are crucial for addressing climate change and conserving the delicate alpine ecosystem. A new study published in Nature Ecology & Evolution provides valuable insights into these issues.

Led by Prof. ZHAO Yan from the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences, the research team analyzed 5,000 fossil pollen samples extracted from two long lake-sediment cores in the Zoige Basin, located at approximately 3,400 meters above sea level on the eastern Qinghai-Tibet Plateau. By integrating biomization, numerical analysis, statistical modeling, and vegetation simulations, they constructed a detailed picture of vegetation dynamics over the past 3.5 million years.

The study revealed that vegetation underwent significant changes: it transitioned from a stable forest during the mid to late Pliocene Period (3.5–2.73 million years ago) to a co-dominance of forest and steppe in the early Quaternary Period (2.73–1.54 million years ago), finally evolving into a meadow-dominated ecosystem around 1.54 million years ago. On orbital timescales, forest and grassland successions displayed distinct cycles of 20, 40, and 100 thousand years, influenced by low-latitude summer insolation and high-latitude ice volume changes.

Notably, the impact of ice volume has shown phased amplification over time. On millennial timescales, frequent shifts in vegetation types have occurred since approximately 1.5 million years ago, primarily driven by the dynamics of high-latitude ice sheets. Vegetation dynamics across various timescales were closely linked to global temperature changes. A past global warming of two to three degrees Celsius relative to pre-industrial levels was identified as a critical threshold for forest expansion and the loss of resilience in the meadow ecosystem on the Qinghai-Tibet Plateau.

This study establishes the longest and most continuous pollen record with consistent resolution globally, providing the first evidence that the meadow-dominated ecosystem on the eastern Qinghai-Tibet Plateau was established around 1.5 million years ago. This ecological transition was driven by the combined effects of global cooling and monsoon evolution.

The findings regarding vegetation resilience and climate threshold effects offer essential insights for predicting how vegetation will respond to future global warming. They also underscore a critical risk: if global warming exceeds two degrees Celsius relative to pre-industrial values, it is likely to trigger a major transformation of the modern alpine meadow ecosystem.