Each year, in a process called senescence, the leaves of autumn trees turn yellow, orange, and red because they stop growing and extract nutrients from the foliage. Leaf maturity also marks the end of the period when plants absorb carbon dioxide through photosynthesis.
Global warming has caused long growing seasons – two weeks earlier than 100 years ago when European trees formed spring leaves, researchers said.
“Autumn is late because the earlier models will be hotter and warmer in the coming century – the growing seasons will be overall longer, and autumn will be two to three weeks later,” said environmentalist Konstantin Johner.
However, Johner and The team of researchers said their findings alter this prediction.
Using a combination of field observations, laboratory tests and modeling, the experts examined data from six European deciduous tree species – European horse chestnut, silver birch, European beech, European larch, English oak and rowan – over the past six decades.
Experts have found that the increase in spring and summer productivity resulting from high carbon dioxide, temperature and light levels actually causes trees to lose leaves earlier.
Fall temperature and day length are the main environmental factors that cause trees to lose their leaves, Johner said. Now, researchers have identified a third factor – a “self-limiting” productivity.
“Now we see, this third big mechanism is going on – (tree) productivity controls itself. If you already do a lot in the spring and summer – if the plant absorbs too much CO2 in the spring and summer, they lose leaves earlier,” he said.
“This is a mechanism we see in humans as well – if you start eating earlier, you will already be full,” he said.
The findings show that trees have productivity barriers, Johner said.
“We can’t put more and more CO2 in the atmosphere, (expect) trees will do more – there are limits,” he said.