© Kris Van Exel
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You might have noticed during an autumn walk: it’s almost All Saints’ Day, but there are hardly any leaves on the ground. That has everything to do with last summer, which was particularly wet.
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According to physicists, exactly when trees lose their leaves depends on a number of factors: the tree species, the drought, the length of the day, the light intensity and the temperature.
Chestnut trees and walnut trees have already lost some of their leaves. But many other species are still green and are only now beginning to change colour. “The wet summer ensures that the trees remain in ‘good’ condition for longer”, says scientific director Koen Es of the Botanic Garden of Meise. He points out that they have been given enough water and have been able to keep up with it. Consequently, they hold their leaves longer. In addition, the wet summer also made trees better able to resist pest insects such as the typesetter or the oak beetle.
What precedes autumn therefore plays an important role for trees. “We are experiencing the opposite of last year. Due to the dry and warm summer, trees lost their leaves en masse at the end of September and in October. This is a result of drought stress,” says Nathalie Sterckx of Natuurpunt.
In any case, it is a misconception that under normal circumstances trees already lose their leaves in September. According to tree expert Hans Verboven of Natuurpunt, October and November are the months when we can walk through a colorful carpet of fallen leaves. “But a lot depends on the weather. When the wind blows hard and the nights get colder, things can suddenly go quickly.”(tg)
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