Trees Shed Leaves Earlier Due to Climate Change

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Each year, in a process known as senescence, the leaves of deciduous trees turn yellow, orange and red when they suspend growth and extract nutrients from the foliage, before dropping from the tree before winter. . Leaf senescence also marks the end of the period in which plants take up carbon dioxide through photosynthesis.

Global warming has resulted in longer growing seasons – spring leaves are emerging in European trees about two weeks earlier, compared to 100 years ago, the researchers say.

“Previous models assumed that because autumns will get warmer and warmer over the next century, fall will be delayed – growing seasons will be longer overall and fall will be delayed by two to three weeks.” said ecosystem ecologist Constantin Zohner.

However, Zohner and a team of researchers said their findings reversed that prediction.

“We actually predict that by the end of the century, the leaves could even fall three to six days earlier,” added Zohner, corresponding author of the article published in the journal Science on Friday.

Using a combination of field observations, laboratory testing, and modeling, the experts studied data that tracked six European deciduous tree species – horse chestnut, silver birch, European beech, larch. European, English Oak and Rowan – over the past six decades.

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Productivity increases in spring and summer that result from increased carbon dioxide, temperature and light levels cause trees to shed their leaves sooner, experts have found.

It had been speculated, Zohner said, that fall temperatures and day length were the main environmental factors leading to leaf loss from trees. Now, researchers have identified a third factor – “self-limiting” productivity.

“What we’re seeing now is there’s this third huge mechanism going on – the (tree’s) productivity is self-constrained. If you already have more in the spring and summer – if the plant absorbs more CO2 synthetically by in the spring and summer they will lose their leaves sooner, ”he says.

“It’s a mechanism that we also see in humans – if you start eating sooner, you will be full sooner,” he said.

The results, Zohner said, showed that trees have productivity constraints.

“We can’t just put more and more CO2 into the atmosphere and (we expect) trees to do a lot more – there are limits,” he said.

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