Planting "urban forests": this is one of Anne Hidalgo's key promises for her second term in Paris.
But is it a viable solution in an urban environment?
This concept is based on the method of the Japanese botanist Miyawaki: express revegetation that would restore a forest ecosystem and make it autonomous after three years.
It made its appearance in Europe a few years ago.
Netherlands, Belgium… these micro-forests mainly grow in urban areas.
And have only a few years of existence in Europe.
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It is therefore difficult to assess the effects of these micro-forests on biodiversity and the cooling they bring to the city.
"The only study that was carried out over 12 years, was carried out in Sardinia, in a mountain area and 60 to 80% of the plantations had not succeeded", underlines Annabel Porté, research director at the National Research Institute for agriculture, food and the environment.
"French forest species do not have the growth rates of the tropical species used by Miyawaki", also insists the researcher.
"And the creation of a forest ecosystem is very slow, very complex", recalls Annabel Porté.
In the 17th century, the cooling effect less important than expected
The scientist has already been there in the 17th century where another micro-forest was planted almost three years ago.
"The hazel trees have grown very well, the hollies too, but the oaks much less," she observed.
The shade cast by this space will therefore be less important and the cooling effect too.
"But I understand that these proposals are attractive for institutions that want to plant a lot of trees," concedes Annabel Porté.
But in the city to fight against global warming "it is not only the quantity of trees planted that counts but the plant surface created", underlines the researcher.
So urban craze for the future or flash in the pan these urban forests?
"For the moment, we lack hindsight," says Annabel Porté.