Why would you want to plant a million trees in the metropolis of Bordeaux?

Trees on the quays of Bordeaux -

• The president of the metropolis says he wants to rely on the private sector and the inhabitants to achieve the ambitious goal of planting a million additional trees.

• For the creators of Tree in Town, “the inhabitants will mobilize to plant trees in squares.

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• Freshness, pollution treatment, carbon storage… The benefits of trees in urban areas are multiple, they point out.

Will the Bordelais do as well as the New Yorkers?

By announcing on Tuesday an ambitious program to plant a million trees in the Bordeaux metropolis over the next ten years, and by explaining that he wants to rely on the population to achieve this, the president of the metropolis Alain Anziani is in any case inspired by the "Big Apple".

In 2007, New York also launched a program of one million additional trees in ten years.

By mobilizing the population through social networks, the goal was achieved in just seven years.

"They organized a lot of events to plant trees, that's what made the operation successful," said Olivier Papin, head of the Bordeaux design office E6, specializing in the environment.

Recalling that the metropolis owns only 5% of land in the territory of the agglomeration, Alain Anziani announced that it would be necessary to work with the private sector and with the inhabitants.

"I am convinced that the population will take ownership of the project"

Alexandre Colin, who heads the Landscapes workshop in Saint-Jean-d'Illac (Gironde), says he was surprised by the “ambitious project” of the metropolis.

“One million more trees is a really big number.

”With E6, he developed specific work on the adaptation of territories to climate change, and the two companies in particular carried out the diagnosis of the islands of heat and freshness of Bordeaux Métropole, and developed the tool Arbre en Ville, on the role of trees in an urban environment.

As in New York, he thinks that “the metropolis will only succeed in its project with the massive help of its inhabitants.

"" I am convinced that the population will take ownership of the project, he anticipates, the demand will be there and the inhabitants will mobilize to plant trees in places.

"Same analysis for Olivier Papin, who observed" a real expectation of citizens to move towards more greening.

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"Create islands of freshness throughout the metropolis"

The fallout from trees in urban areas is manifold.

"This brings freshness and nature to the city, treatment of atmospheric pollution, well-being, and carbon storage even if this is not the main argument because it is marginal compared to the emissions of the metropolis [which are of the order of 5 million tonnes per year, when a tree absorbs between 1 and 5 tonnes of Co2 in its lifetime]… ”

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, Alain Anziani assures us that with "the temperatures which keep rising, it is necessary to create islands of freshness throughout the metropolis" and that with "a very large number of islands we can have an influence on the climate of the metropolis.

"If that does not change at the scale of the whole metropolis, it can in any case refresh a place", according to Olivier Papin.

"We must hope that not everything is planted only in the periphery"

Once the announcement has passed, many questions will now have to be addressed.

“We must hope that everything is not planted only in the periphery, suggests Alexandre Colin, it will also be necessary in the heart of the metropolis: this will make it possible to offer spaces of freshness where it is lacking.

"The landscaper thinks in particular of" the course of the Stewardship, which is hyper-mineral and very dark, it is the typical example of what not to do.

"The major difficulty in these places," it is networks which pass underneath and which will have to be deviated, but we know how to do it, it is a question of means.

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The new mayor of Bordeaux, the ecologist Pierre Hurmic, had made revegetation a strong axis of his municipal campaign, while the city, with a tree-lined heritage of 19 m2 / inhabitant, is only in 9th position in the ranking cities of more than 200,000 inhabitants the greenest in France. 

At the level of the metropolis, the activity zones and the commercial zones, "like Bordeaux-Lac or Rives-d'Arcins" are also strategic because they are "the hottest zones of the territory, because of their flat roofs which take the heat well and their parking lots which are not shaded.

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Wanting to plant tall trees would be "a mistake"

Another question: what to plant, especially when global warming is changing the situation.

“Some trees are struggling to develop, notes Alexandre Colin,“ Bordeaux metropolis will therefore have to broaden its range of tree species to be planted.

And above all you need a mix of species, 15 to 20 different in the same street.

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Our dossier on global warming

As for the size of the trees, and knowing that it takes three years for a tree to reach two meters in height, Alain Anziani warned that he wanted them "sufficiently large, so that we immediately have good visibility.

»Which is a mistake according to the landscaper.

“Even if visually it is stronger, it is better to plant young trees, this is how they adapt best.

"Another issue will be to know who is going to maintain them, because with the heat waves we are experiencing, we will have to irrigate", warns Olivier Papin.

A first urban microforest in Mérignac?

The president of the metropolis also announced that in his plan, he intended to create urban microforests.

To start in his own town of Mérignac.

"La Poste has agreed to give us 1,600 m2 of land so that we can do an urban microforest," he explains to

.

We would thus have in the very center, right next to the media library, an island of freshness, and it would be a place of relaxation for the inhabitants.

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Urban Microforest is a method of planting native microforests, developed by Japanese botanist Akira Miyawaki.

“This consists of planting very young and very tight trees, up to 16 plants per m2,” explains Alexandre Colin.

The idea is to put the plantations in competition, which allows a natural selection and especially to make the trees grow twice as fast.

Personally, I am not convinced, because this can be a way of making money while knowing that trees will not survive, and there is a risk that the tree will be weakened.

There is still some ground to be cleared, before the project really takes root.

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