Japanese knotweed is an increasingly invasive plant in the North.

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B. Toussaint / Conservatory of Bailleul

  • For several decades, exotic plants have spread dangerously in nature, sometimes causing the extinction of rare species.

  • Today, there are 42 animal species and 40 invasive plant species in Hauts-de-France.

    Against 14 animal species and 29 plant species listed in 2015.

The invasion of biodiversity profaners.

It could be the title of a film telling how, for several decades, exotic plants have been spread dangerously in nature, sometimes causing the extinction of rare species.

But the scenario is not a fiction.

This is a report drawn up by the botanical conservatory of Bailleul, in the North, for ten years, through an awareness guide intended for the general public *.

The third edition has just been published with a worrying observation: invasive alien species are more and more numerous.

Threat to biodiversity

Six years ago, 14 animal species and 29 plant species were listed.

They are now 42 and 40 respectively. We know more or less the damage caused by exotic fauna: Asian hornets, American crayfish, Florida turtles or even ring-necked parakeets.

The scourge of flora from elsewhere is often ignored.

The first threat concerns biodiversity.

"Instead of coming locally to enrich it, these plants form dense stands of a single species and the others are declining", explains Benoît Delangue, in charge of scientific missions at the Conservatory.

Because there is no regulation in their development.

"They come from the other side of the world and do not bring with them the organisms that regulate their development", specifies Benoît Delangue.

Navigation problems

Sometimes the nuisance is significant.

Japanese knotweed, which grows along roadsides, especially on the Lille ring road, can hinder the visibility of motorists with its size being able to reach more than two meters.

The Cradle of the Caucasus can cause lesions and burns if it comes into contact with the sap.

In 2020, a group of scientific and technical experts was set up to manage the management of these invasive plants.

"Eradication is very often impossible for these species which proliferate very quickly", explains Benoît Delangue.

Multiplication of world trade

And getting rid of them can be expensive.

On the Somme Canal, the authorities have to spend around 200,000 euros each year to clear the navigation routes blocked by an aquatic plant with a barbaric name.

What other solutions?

“Act upstream and prohibit the sale of certain species,” says Benoît Delangue.

Regulations have been implemented for several years, but the increase in global trade favors the spread of exotic plants that travel with goods.

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* "Invasive exotic plants of Hauts-de-France", free (except postage costs).

PDF version available on the Bailleul Conservatory website.

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