Uptake Of CO2 By Trees May Be Substantially Overstated; Study Found Growth Stopped Months Before Photosynthesis Did

[hatrack]

Last edited Sun Jun 14, 2026, 12:40 PM - Edit history (1)

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. 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. Other uses of carbon are typically shorter lasting. As fossil fuel emissions leave more carbon dioxide in the atmosphere for trees to absorb, climate scientists expect the land-based carbon sink to remain stable or grow over the 21st century. But many of the models estimate the uptake using the levels of photosynthesis, rather than actual wood growth.

“Right now, most models assume that if you have photosynthesis, you have growth. We find that’s not the case,” said Mukund Palat Rao, a carbon cycle scientist at the Lamont-Doherty Earth Observatory at Columbia University and lead author of the study. “Just because there is more photosynthesis might not necessarily mean more tree growth in the future.”

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.

EDIT

https://www.theguardian.com/environment/2026/jun/13/trees-store-less-carbon-than-thought-study

[bucolic_frolic]

1. That's crazy

I watch my trees sometimes closely, when pruning. Growth in bark swells well into the fall, when the leaves have been drying for 2-1/2 months. In spring the sap goes up and makes leaves, which then collect sunlight. Then the leaves stop growing, and the sap returns to the roots. The new wood growth in several species is light brown or even orange.

[OKIsItJustMe]

2. New Research Indicates That in the Future, Trees May Store Less Carbon Than Expected

Columbia Climate School

June 12, 2026

Highlights

• Researchers found that oak forests can continue taking up carbon after their seasonal wood growth has ended.
• Aridity and heat limit tree growth more strongly than photosynthesis.
• As the climate warms, forests may keep absorbing carbon without storing as much of it in wood.
• The findings suggest climate models may overstate the long-term carbon sink provided by forests.

It’s intuitive to think that if a tree is photosynthesizing, it’s also growing. But that’s not necessarily so—and a new study of oak trees, published in the journal Science Advances, found that even as they photosynthesize late into the year, their growth stops by mid-summer.

Much of the long-term carbon storage that forests provide depends on trees converting the carbon they absorb through photosynthesis into new wood. Many researchers have predicted that rising atmospheric carbon dioxide (CO2) levels will enhance photosynthesis and stimulate tree growth, putting some of that planet-warming carbon into long-term storage inside wood. However, the observed decoupling of photosynthesis from growth suggests that increased carbon uptake does not necessarily translate into greater wood production. Instead, some of the absorbed carbon may be used to produce foliage or used in short-lived metabolic processes rather than being locked away long term, reducing the amount of carbon stored in forests compared with previous expectations.

…

“Right now, most models assume that if you have photosynthesis, you have growth. We find that’s not the case,” says lead author Mukund Palat Rao, an ecoclimatologist at Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School. “Just because there is more photosynthesis might not necessarily mean more tree growth in the future.”

…

Mukund Palat Rao et al. ,Decoupled carbon assimilation and growth responses to aridity in temperate deciduous oaks.Sci. Adv. 12,eady7139(2026).DOI:10.1126/sciadv.ady7139