Trees do not grow faster with higher carbon dioxide uptake

The amount of carbon dioxide2 That trees can pick up is exaggerated in current climate models. Models assume that carbon dioxide is very high, especially in cold, dry forests2-take.

To reduce climate change, we need far fewer greenhouse gas emissions around the world. Trees can help us with that. After all, they put carbon monoxide2 of air in its trunk, branches, leaves, and root web. Therefore, forests play an important role in the fight against climate change. An international research group says current climate models may overestimate this contribution. Their research shows that trees don’t necessarily grow faster if the amount of carbon dioxide is2 The air increases – something most models assume.

ko2-to abundant

During their lifetime, trees absorb carbon dioxide2 From the sky through their leaves. Through the process of photosynthesis they convert this – with the help of sunlight and water – into sugars and oxygen. The sugars are used by the tree for growth. For example, greenhouse gases turn into wood, leaves, and roots.

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If you look purely at photosynthesis, it seems logical that more carbon dioxide2 In the air causes more trees to grow. Thus, more greenhouse gases will lead to more plants; As long as you provide enough space for them to grow.

Climate modelers usually assume that the relationship between carbon dioxide2– Uptake and growth are nearly linear: twice the amount of carbon dioxide2Absorption means poor growth. But this is not the whole story. More and more studies are showing that other environmental factors play a role as well. Think about the temperature and the amount of water and nutrients in the soil. If you want to predict how trees will react to climate change, it is important to know the factors that can inhibit growth.

tree trunk rings

In its new publication, an international research group shows that more carbon dioxide2 It does not mean more tree growth. To do this, the researchers studied trees in 78 forests in North America, Europe, Japan and Australia. There they measured the amount of carbon dioxide2 Existing trees can suck. They did this with measuring towers that measure carbon dioxide2Concentration and recording of wind currents in the air. They combined these measurements with data on tree growth, which they obtained from the International Tree Rings Database. Cores were excavated from trees for tree ring measurements. The width of each ring tells you how fast the tree is growing.

Read also: Climate models paint a very favorable picture of carbon uptake by tropical forests

In their analysis of these measurements, the researchers did not find the linear relationship between carbon dioxide2Recording and growth of trees on which climate models are based. if CO2The uptake of trees increased, and this was not accompanied by an increase or decrease in tree growth. This is especially true of cold, dry regions, the researchers wrote. This is in line with a previous study on the effect of carbon dioxide2 on the growth of tropical forests over the past 500,000 years. This research, led by the University of Amsterdam, was published in early May in Science† In it, the researchers also wrote that the effect of carbon dioxide2 Overestimate the growth of trees in the air.

Wooden cores for measuring tree rings.
Pictured: Antoine Capone

to breathe

“These results confirm that the relationship between photosynthesis and growth is not as simplistic as the current representation in models,” American researchers Julia Green and Trevor Keenan wrote in a simultaneously published commentary. But, keep it up, the study has some flaws. This is how plants “breathe” some of the carbon dioxide2 It is absorbed back into the air during photosynthesis. So not all absorbed carbon is available for growth. Researchers do not take this into account.

Furthermore, Green and Keenan noted that only tree rings were considered. But trees don’t just store carbon in the form of wood. They also use it for the growth of the root system and leaves. Hence the woody growth does not quite correspond to the total amount of carbon sequestration.

Despite these limitations, the research fits with the trend of publications showing that current climate models overestimate the contribution trees can make. This indicates that scientists do not yet fully understand how trees grow.

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