Every winter, the blooming of its thousands of small yellow flowers illuminates and perfumes the Côte d’Azur, but the mimosa, an invasive and highly flammable exotic plant, also represents a danger in the massifs.
A tree of the acacia family, the mimosa comes from the southern hemisphere, more particularly from Australia for the “acacia dealbata” or “winter mimosa”, imported by the English in the mid-19th century for its ornamental qualities.
A Lord planted it in the garden of his villa in Cannes, on the French Mediterranean coast, and the species very quickly colonized the surrounding natural spaces.
It has brought delight to Grasse perfumery and now attracts tourists: festivals, flower parades, excursions punctuate the month of February on the 130 km of the “mimosa route”, between Bormes les Mimosas (which was only “Bormes ” until 1968) and Grasse.
But this express acclimatization is not good news for local ecosystems because the winter mimosa gradually suffocates endemic plants and micro-habitats, while making the massifs more vulnerable to fires.
“The mimosa grows one meter per year on average,” Fanny Moreau, project manager at the Provence-Alpes-Côte d’Azur Conservatory of Natural Spaces (Cen-Paca), explains to AFP. “And what’s more, it emits toxic substances which will limit the growth of surrounding species.”
And “it is a very flammable gasoline, the self-combustion of which also releases a gas which activates the fire”, adds Christophe Pint-Girardot, forestry technician from the National Forestry Office (ONF) in the Estérel massif .
Worse: fires encourage the dispersion of its seeds. And this champion of reproduction also produces new plants by suckering – when the roots emerge from the ground – and stump shoots.
“The more we cut it, the more it grows back, it’s a vicious circle,” summarizes Ms. Moreau.
– With a backhoe –
If there is no longer any question of attacking the almost entirely colonized valleys, the ONF is at least seeking to confine the mimosa by attacking subjects that are still isolated, such as in the national forests of Estérel, a site making part of the European network for the protection of Natura 2000 biodiversity.
On the tufts of young stems which grow back after clearing, “we keep the most important stem, so that it captures all the water and mineral salts from the soil”, explains Mr. Pint-Girardot.
“When the individual is adult, we remove 1.30 m of the bark and the first centimeters of the periphery of the trunk, in order to weaken the mimosa without stressing it, because if we stress it it will re-shoot everywhere by the roots,” he adds.
But sometimes you have to be more radical, as on the Bombardier site, still in the Estérel massif, crossed by a DFCI track (Defense of the forest against fire), the surroundings of which must remain cleared of brush.
After the last clearing in December 2022, Cen-Paca, manager of this private site, and the urban services responsible for the Natura 2000 site, proceeded to uproot the mimosa stumps in March 2023.
Where the excavators have passed, the mimosa has sometimes reappeared in clumps, but in areas where mechanical stump removal was not possible, the ground is already covered with a carpet of mimosa plants almost a meter high .
For seven years, manual uprooting of new shoots is therefore planned, in spring and autumn. A partnership with the justice system makes it possible to make them work of general interest, but the organizers also call on volunteers.
“It’s a control plot, we want to see the effectiveness of the method. And then we’ll see what we want to implement elsewhere,” explains Jean-Olivier Pichot du Mezeray, Natura 2000 facilitator within the agglomeration. .
But there is no question of depriving private gardens of the little fluffy sun: there are more than a thousand species of mimosa and nurseries offer varieties with flowers that are just as pretty and much less invasive.
published on February 25 at 9:01 a.m., AFP