Since mid-July, heat waves and drought have caused the leaves of trees in several cities in France, including Paris, to turn color and fall off.
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what exactly is going on
In order to fully understand the phenomenon, it is necessary to study the stomata. These small openings, located on the surface of the leaves, allow the tree to sweat and thus cool down, explains Michel Labrecque, director of the scientific research and development department of the Montreal Botanical Garden.
The photo was taken in a park near Paris
When the tree feels that there is less water in the soil, as is currently the case in France, it closes its stomata to be able to store the water it has already absorbed through its roots. The expert emphasizes that this is a completely normal reaction that survives the tree during periods of drought.
But by stopping the tree from draining water through its stomata, the tree is in a sense sacrificing its leaves, which, when exposed to heat, will dry up and eventually fall off.
Do we need to worry?
The phenomenon is not dangerous in itself. But because of climate change, it could become more common and have dramatic consequences, warns Michel Labrecque.
“It won’t kill the trees in the short term, but it does make them a bit vulnerable later on. If it happens too many times each year, it can be really damaging,” he says.
“In the long term, it can weaken the trees and make them more susceptible to diseases, insects and various climatic stresses.”
France is on the verge of its third heatwave of the summer, with temperatures that can reach 40ºC. The country has already broken records for the number of very hot days since the beginning of summer.
The mercury could reach 40°C in France in the coming days.
Will the leaves grow back?
Michel Labrecque suggests that if the leaves fall in the middle of summer, a second leaf formation could occur before autumn. However, a second foliage is not always good news, especially during droughts, as the tree has to draw on its stored resources, he specifies.
“It’s good for the landscape, but it’s not necessarily good for the tree to have two leaves in the same summer. It can influence the development of the following year and cause weaknesses, make them vulnerable.
If the leaves fall off in late summer, new leaves will not sprout until the following year.
Possible in Quebec?
While it’s not impossible to see such a phenomenon in Quebec, it’s unlikely, claims Michel Labrecque. The weather forecasts for the next few years do not actually point to major periods of drought.
In coming years, the effects of climate change in Quebec are likely to be felt more strongly in winter, with episodes of mild spells and freezing rain, for example.