Contrary to previous assumptions, increases in the concentration of atmospheric CO2 over the last 150 years have not led to more rapid growth of tropical trees, reports a study published online in Nature Geoscience. Increased CO2 concentrations had been assumed to accelerate the growth of tropical trees, which would in turn remove carbon from the atmosphere and potentially slow climate change.

Peter van der Sleen, Pieter Zuidema and colleagues analysed tree rings from tropical forests in Bolivia, Cameroon, and Thailand. They found that the increasing atmospheric CO2 concentrations over the past 150 years have allowed trees to photosynthesize more efficiently, as was expected. However, the width of tree rings, which reflects the growth rate of the tree, showed no evidence for an increase in growth resulting from higher CO2 concentrations in either understory (shade-dwelling) or canopy trees. Instead, the tree-ring data suggest that trees in the tropics may not be a sink for the increasing CO2 concentrations in the atmosphere, as was previously believed. This finding suggests that our concept of the impacts of climate change on the carbon cycle may need to be revised.

In an accompanying News and Views article, Lucas Cernusak writes that “further research into why the results of the tree ring record diverge from forest inventory observations and model predictions will be essential for understanding how increased CO2 concentrations and a changing climate will affect tropical forests and the global carbon cycle.”