In 1999, storms Lothar and Martin devastated almost a million hectares of forest in France.
Usually during these fall/winter storms, the trees have already lost their leaves. And the wind passes, rushing without too much difficulty through the branches. But today, the start of autumn was mild, and the trees were still full of leaves. Problem: this provides wind protection. With gusts of 170km/h on the coasts, 130km/h inland, expected with storm Ciaran, according to Météo France forecasts, the branches will be under strong pressure, leading to a risk of branches falling and even uprooting. of trees.
The rains of recent weeks also risk causing trees to fall, because the soils are waterlogged and malleable, warns agroclimatology specialist Serge Zaka. Thus, the earth is looser and the roots of the trees will resist less deeply. Certain species could be more at risk, such as maples and cherry trees, for example, which have shallow roots, unlike pines.
“With gusts of more than 90km/h, we must expect falling branches, more than 110km/h, falling trees, and at more than 140km/h, sections of forests will fall “.
Stéven Tual, meteorologist
Sections of forest falling are reminiscent of the Lothar and Martin storms of 1999. In 1999, 6% of the French forest had suffered damage, or almost 1 million hectares. Since then, 65% of this forest has regenerated naturally. For the rest, the National Forestry Office (ONF) had to plant trees, with new species more adapted to the terrain and storms (maritime pine, sessile oak and Douglas fir for example). It is not known whether Ciaran will be as violent, but the ONF advises all residents of northwest France to stay away from trees. He recommends avoiding walks in the forest on Thursday and Friday, but also this weekend, because there will remain a risk of falling trees even after the storm has passed.