Trees that grow faster die younger, a study of tree rings has confirmed. Many trees worldwide are already dying more quickly as a result of rising carbon dioxide levels and temperatures. This means that existing forests will store less carbon than we thought, worsening climate change.
鈥淎ll the extra carbon trees are taking up will come out of the system faster,鈥� says Roel Brienen at the University of Leeds, UK. 鈥淭his effect is already happening in some places, such as the Amazon.鈥�
It has long been suspected that faster-growing trees die younger, and this has already been shown to be the case for some specific trees. Brienen鈥檚 team has now confirmed that this is widely true by analysing existing tree ring data from around the world.
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Exactly why fast growth leads to early death is unclear. It could be because trees that grow faster reach their maximum size sooner. 鈥淭his is the most simple explanation, but we can鈥檛 conclusively say why,鈥� says Brienen.
Several studies have already found that more trees are dying in forests, including the Amazon. These new findings help explain why, though other factors such as more intense droughts are probably also playing a role, says Brienen.
If CO2 levels and temperatures were stable, undisturbed forests would be in equilibrium, releasing as much CO2 as they take up. However, rising CO2 levels and temperatures have so far boosted overall growth, meaning existing forests are taking up more carbon. In fact, they are soaking up around a third of the all the extra CO2 we are pumping into the atmosphere.
Many models used for forecasting CO2 assume that this growth boost will continue, but simple simulations by Brienen鈥檚 team suggest that carbon uptake will decrease as more and more trees die and release carbon. A study earlier this year found that carbon uptake is already decreasing.
This applies only to existing, undisturbed forests. Planting new forests will still help store lots of carbon. But it is best to plant a mix of fast and slow-growing species to ensure it remains locked away, says Brienen.
Nature Communications
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