Study shows storms, dryness speeding up biomass turnover in Amazon forest

Powerful storms and drier air are speeding up the natural biomass turnover in the Amazon rainforest, potentially reducing its ability to store carbon for long periods of time, researchers have found.

The study, led by the South China Botanical Garden (SCBG) of the Chinese Academy of Sciences, together with Cornell University and other international partners, was published in the journal Nature Climate Change.

Tropical forests like the Amazon hold more than 60% of the world's plant biomass, making them critical players in regulating the global climate. But their role as carbon storage depends on how long carbon stays locked in trees and other vegetation before being released back into the air. Scientists call this the carbon residence time. The study shows this residence time is shrinking across the Amazon. As the atmosphere becomes drier and convective storms become more active, trees are dying and being replaced faster than before.

Earlier research on tropical carbon sinks has focused mostly on tree growth and productivity. Much less attention has been given to tree death and biomass turnover. Most past studies also relied on data from small, local forest plots.

"Tropical forests are highly complex and vary greatly from place to place," said Wu Donghai, a researcher from the SCBG. "Limited field plots cannot fully capture large-scale patterns and drivers of biomass carbon turnover."

To solve this problem, the team combined satellite images with long-term records from forest plots across the Amazon. This allowed them to map tree death and biomass turnover across the entire region. Using machine learning, they then evaluated how different environmental factors affect carbon turnover time.

The results show that biomass carbon turnover time varies widely across the Amazon and responds to environmental changes in strongly nonlinear ways. Convective storms turned out to be an even stronger influence than drought-related stress.

The researchers predict that, by the end of this century, carbon turnover time in Amazonian forests will shorten by about 3% on average under a low-emissions scenario. Under a high-emissions scenario, it could shorten by as much as 15%.

Wu said the findings help scientists better understand what keeps tropical forest carbon sinks stable. They also provide key support for improving Earth system models, which are used to determine future climate change trends.