OVER the past 100 years, global warming has caused many high-altitude forests to shift upward. A recent Chinese study reveals the reason behind the phenomenon. Researchers from the Institute of Tibetan Plateau Research under the Chinese Academy of Sciences analyzed 8-10 years of trees and shrubs observation data in the same region in southeastern Tibet. They found that under a spring warming of 1 degree Celsius, growth advances by 2-4 days in trees but delays by 3-8 days in shrubs. The different response to warming was due to shrubs being much more sensitive than trees to chilling environments. The study has been published in the journal National Science Review. The researchers then had a global meta-analysis combined with a process-based growth model to explore drivers of growth shifts in response to warming across 11 alpine treelines in the Northern Hemisphere. Treeline is the elevation at which trees no longer grow. The analysis proved that trees are more sensitive to spring warming than shrubs as expected. (Xinhua) | 