The amount of carbon dioxide absorbed by trees is exaggerated

The role of trees in combating climate change may be overestimated. who – which An international group of scholars concluded Thursday at Science† They have shown that trees sometimes grow less quickly than climate models predict based on the amount of carbon dioxide.₂ Which sucks trees from the sky.

Trees absorb greenhouse gases through their leaves₂ Up in the air. They convert it into sugars through the process of photosynthesis. They grow on this energy source: they process carbon (C) from the air into additional woody tissues.

Most climate models assume a linear relationship between carbon dioxide₂Recording and tree growth. If the carbon dioxide concentration₂ Increases in the air, the idea is that the growth of trees will increase proportionally. Climate skeptics sometimes refer to what’s called CO₂The effect of fertilizing. More from CO₂ In the air provides additional growth of the plant. This is really useful.

less flow

But the now-published study shows that this relationship does not always hold. Sometimes the growth of the tree lags. This is especially the case in drier and colder regions, as well as in old forests, the researchers say.

They collected data from 78 so-called forest flow Studies in which carbon dioxide is exchanged₂ between the atmosphere and forests over time. They combined that with data from tree growth in the same or adjacent areas. They got this data from tree ring databases – the growth rate can be read from the width of the growth rings.

“Existing models are too simplistic,” said Roel Brennen, professor of forest ecology at the University of Leeds. “They cannot simulate complex physiological processes in plants at all.”

at Post a comment at a time Julia Green and Trevor Keenan of the University of California, Berkeley write that tree growth goes beyond just carbon dioxide₂ Depends on. You also have the available amount of water and nutrients in the soil and the temperature. All of them can affect growth.

This is not the first time that the linear relationship between carbon dioxide₂Registration and tree growth are questionable. There was already a post in early May Science Written by, among others, a researcher from Amsterdam and researcher at Wageningen Which showed that the effect of carbon dioxide₂ The growth of tropical forests in West Africa over the past 500,000 years has been less than previously thought – water and forest fires played a much larger role. The authors therefore suggest that the contribution of CO₂– Fertilization must be modified in predictive climate models.

And two years ago, Australian researchers For example, eucalyptus trees are exposed to increasing concentrations of carbon dioxide₂ Do not grow fastertemper natureApril 8, 2020). The leaves took in more carbon dioxide₂ But the trees did not capture the extra carbon that was absorbed. Ultimately this carbon is in the form of carbon dioxide₂through the bottom just as difficult again.

Tree rings don’t say everything

The research now published has some shortcomings, Greene and Keenan write. Trees not only store above-ground carbon in the growth of timber, but also, for example, in their leaves and root system. So looking at tree rings doesn’t paint the full picture.

“In addition, trees can temporarily store carbon in reserves throughout the plant, sometimes using it for growth after many years,” says Brennen. Correlation in time, from CO₂So uptake and growth are also complex.

Green and Keenan also note that the researchers used only trees in the hospital ko₂ taken, while some of that CO₂ Released again through the bottom. They write that it is better to convert net carbon dioxide₂sign out.

However, they also concluded that current climate models likely overestimate the extent to which trees absorb carbon.