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Science
Jun 16, 2026
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Trees May Store Less Carbon Than Hoped, Study Suggests

AI Summary
A new study suggests that trees may not store as much planet-heating carbon as previously thought, as photosynthesis does not always lead to wood growth. Researchers found that trees stopped growing months before photosynthesis stopped, impacting carbon sequestration models.

The Carbon Storage Conundrum

Trees may not be able to store as much planet-heating carbon as hoped, a study suggests, with researchers finding photosynthesis does not always lead to wood growth.

Photosynthesis and Wood Growth Decoupling

Scientists studied 137 sites across the US and found trees stopped growing months before the point in the year at which photosynthesis stopped. Forests are a vital defence against climate breakdown but their power depends in part on how much carbon dioxide they can convert into wood, which keeps the planet-heating molecule out of the atmosphere for decades and centuries.

The Data Analysis

At sites in the eastern US, the researchers found about 36% of yearly carbon uptake occurred after the tree growth stopped in late summer. At sites in California, it was about 26%. More detailed measurements at four sites showed wood growth was restricted to periods of low aridity and temperature, which are becoming rarer as the global rise in temperature makes heatwaves and droughts more common.

The Impact Analysis

“The moment you have dry and hot conditions, growth activity stops pretty instantly, while photosynthesis seems to continue at a slightly decreased rate,” said Mukund Palat Rao, a carbon cycle scientist at the Lamont-Doherty Earth Observatory at Columbia University and lead author of the study. This decoupling of photosynthesis and wood growth has significant implications for carbon sequestration models.

The Prediction

The researchers are now studying whether the decoupling of photosynthesis and wood growth they observed can be seen in other tree species and regions. They said their results showed the capacity of forests to store carbon over long periods depended on how much carbon was absorbed and then directed towards wood growth. If more of the absorbed carbon were to flow toward transient uses – such as foliage and internal processes – the power of forests as carbon sinks would fall. “Earth system models that assume consistently tight coupling between photosynthesis and growth may therefore overestimate future forest carbon sequestration under rising atmospheric moisture demand,” the researchers wrote.