What’s Going On Here?

New research predicts that global heating will cause trees to drop their leaves three to six days earlier than expected. Consequently, forests will absorb and store significantly less carbon dioxide than scientists had hoped.

What Does This Mean?

In preparation for the coming winter, leaves of deciduous trees change their colour while suspending growth and extracting nutrients. This process is called leaf senescence and marks the end of a plant’s ability to absorb carbon dioxide through photosynthesis.

Previous models assumed that autumn would be delayed by two to three weeks due to rising temperatures. However, ecosystem ecologist Constantin Zohner and a team of researchers have tracked six European deciduous tree species over the last six decades and predict that by the end of the century, global heating will make trees shed their leaves earlier.

The new findings highlight the productivity constraints of trees, adding to the already known environmental factors that cause trees to lose their leaves. Zohner explains that plants will lose their leaves earlier if they already absorb more carbon in synthesis through spring and summer. This increased productivity is caused by elevated CO2 in the atmosphere and Zoner warns that “we cannot just put more and more CO2 in the atmosphere and (expect) trees will just do so much more.”

Why Should We Care? 

Scientists are still working out exactly how much this switch from a delay to an advance in leaf-fall will reduce trees’ uptake of carbon, but first estimates predict that temperate forests will store about 1 gigatonne less carbon each year, roughly a tenth of what humanity emits annually.

On top of that, rising temperatures will not only lead to an earlier spring and autumn but recent research has also shown that deforestation and the climate crisis have reduced the lifespan of trees significantly. Therefore, forests will provide less of a brake on global heating than hoped.

Be Curious!