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In Île-de-France, the challenge of planting micro-forests to slow down global warming

In the Paris region, volunteers are using a Japanese technique to create “mini-forests”. Their objective: that these small green spaces help to slow down global warming, promote biodiversity and make it possible to fight more effectively against the increasingly frequent heat waves in the capital.

On a rainy Saturday in January in the southern suburbs of Paris, Kader, 9, is busy with a shovel in his hand. In the roar of car engines coming from the highway a few meters away, he tries to dig a hole to plant a shrub, barely taller than him. After a few minutes, he throws down the shovel and digs out the earth, turned into mud by the rain, directly with his hands.

Beside him, his grandmother and a dozen other volunteers of all ages, hats on their heads and boots on their feet, perform the same gestures. All responded to the call from the Boomforest association. For several years, it has been at the initiative of creating “micro-forests” in urban areas, particularly in the Paris region. After Nanterre, Cergy-Pontoise and the 18th arrondissement of the capital, it is now in Chevilly-Larue, in the Val-de-Marne, that she wants to recreate a forest area.

“I jumped at the chance to do something concrete to fight climate change and show my grandson how to plant trees,” said Grazia Valla, 79, Kader’s grandmother. “He loves the Chevilly shared vegetable garden. Every time I take care of him, he asks to go there,” she continues, casting an affectionate look at the little boy. “It was a continuation of his interest in trees and plants.”

“It’s really something special to plant a tree”, testifies, for his part, Maxim Timothée, 31 years old. “A tree is not an object and it is at times like these that you realize that. Now I feel connected to the life of this tree: I want to protect it because it is I who planted it.”

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Micro-forests are multiplying in France in the hope of combating climate change. © Charlotte Wilkins, FRANCE 24

The Miyawaki method

Micro-forests like the one that will soon see the light of day in Chevilly-Larue are inspired by the Miyawaki method – named after the Japanese botanist Akira Miyawaki who developed it in the 1970s. By studying the trees that the Japanese leave grow naturally around temples or shrines, he realized that they formed forests, certainly modest in size, but which did not require any maintenance and which, above all, were more resistant than those created by human will.

Based on this observation, he therefore invented a method intended to recreate as much as possible these “native” forest spaces, which would have grown in a given place if it had never been modified by humans. It is based on three main principles: the soil must be rich, the trees planted densely – three per square meter – and local species must be favored.

The key benefits would be numerous: according to Boomforest, these forests would grow up to ten times faster than conventional plantations, thus helping to cool the areas where they are planted, capturing more CO2, and offering a new nest of biodiversity.

So many promises that have allowed the Miyawaki method to be exported to the four corners of the globe. Micro-forests have sprung up in South America, Lebanon, Jordan, India and, for some years now, in Europe. In France, Boomforest is therefore behind various projects on the outskirts of Paris, but other plantations have sprung up in Toulouse, Bordeaux and even Mulhouse.

In Seine-Saint-Denis, the city of Montreuil saw the birth of one of the first French projects of its kind in 2018 thanks to the participatory budget of the City of Paris. Located between the flea market stalls and the ring road, “about 95% of the 1,200 young trees that were planted there survived”, according to Guillaume Dozier, volunteer for Boomforest. “The trees have now reached a height of almost four to five meters,” he says, adding that the biodiversity of the micro-forest is now in full expansion. “Every time we go there, we notice more and more insects and birds that weren’t there before.”

The young trees are planted very close to each other, in accordance with the method developed by the Japanese botanist Akira Miyawaki.
The young trees are planted very close to each other, in accordance with the method developed by the Japanese botanist Akira Miyawaki. © Charlotte Wilkins, FRANCE 24

As in Montreuil, the volunteers from Chevilly-Larue strictly follow the recommendations of the Japanese botanist. So they plant the young shrubs a few centimeters from each other. “Planting a single tree has been shown to have the same cooling effect as ten air conditioners. But trees are social and do much better when planted in the company of other trees, explains Guillaume Dozier. give each other shade and can exchange water, nutrients and information. If one of them is attacked by an invasive species, they can warn the others. For example, they will bitter their leaves to make them less edible to the attacker.”

Oaks, ashes, beeches and willows in the center, hazel trees, holly, spindle on the edges… All the young trees planted are also local French species, adapted to the climate of the region, assures Boomforest. A total of fifteen different species of plants will be used for this micro-forest.

Refresh the capital

In addition to the benefits for the environment, through these projects, defenders of the Miyawaki method hope to be able to cool Paris, on the front line during increasingly frequent heat waves. In the summer of 2022, the mercury repeatedly exceeded 40°C in Paris: a furnace when the capital has only 9% trees. To cope, the mayor of Paris has therefore promised to plant 170,000 trees by 2026, essentially following the Japanese method.

To carry out this project, it will still be necessary to find the available spaces, nuance however Guillaume Dozier. “The problem with Paris is that it’s a bit of a museum city…”, he laments.

Volunteers hope the mini-forest will help slow the effects of climate change.
Volunteers hope the mini-forest will help slow the effects of climate change. © Charlotte Wilkins, FRANCE 24

Faced with the expansion of micro-forests, however, some dissonant voices are being heard. Some researchers point the finger in particular at the cost generated by their implementation – 3,000 euros per 100 m² according to Boomforest – and express doubts as to their sustainability. In Europe, one of the rare scientific studies (2010) on the effectiveness of the Myawaki method, carried out in a micro-forest in Sardinia, thus reports tree mortality of between 61 and 84% after twelve years.

The figures and benefits often put forward by the promoters of the method – richer biodiversity, greater carbon storage – are also largely drawn from the publications of the Japanese botanist and his supporters and few third-party studies exist.

At the end of the afternoon, despite the increasingly heavy rain, Kader, Grazia, Maxim and the other volunteers managed to plant trees on approximately 250 m². Eventually, nearly 800 m² should be reforested. Over the next few months, Boomforest volunteers will return to Chevilly-Larue several times to observe the development of the new forest and ensure its maintenance. With one hope: that in 10 years, it will look like a hundred-year-old forest. “I hope my grandson will come for a walk there and say to himself: ‘Hey, I really did something here'”, concludes Grazia Valla.

This article was adapted from English by Cyrielle Cabot. The original can be found here.

France 24-Trans

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