Plant invaders are a headache for conservationists

Plant invaders are a headache for conservationists

This article has been reviewed in accordance with Science


Garden favorite or invasive pest?

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Garden favorite or invasive pest?

The tall, attractive exotic has showy plumes and can make itself at home on the coast, in the city, or even in your garden.

But conservationists warn that cortaderia cilona – or pampas grass – is a harmful invasive species threatening parts of southern Europe.

Also known as 'feather duster', pampas grass is sold as an ornamental plant despite appearing in a rogue exhibition featuring hundreds of Europe's worst invasive species.

At the International Union for Conservation of Nature (IUCN) World Congress, which concluded this week in Marseille, a movement called for “urgent action” to restrict and eventually eradicate the plant outside its native South American habitat.

Conservation groups and ministries, many from Spain, said they were “concerned that today their seeds can be purchased easily and cheaply anywhere in the world, without legal restrictions, through various internet platforms.”

This case highlights the difficulties of stopping the spread of invasive plants in the face of low awareness and massive international online trade that exposes exotic species at the click of a button.

“You see more clearly the impact of animals – they are a predator that destroys prey. But plants can have a very severe impact,” says Piero Genovesi, who heads the IUCN's Specialist Group on Invasive Species.

“It's less noticeable at first, but then it becomes huge.”

Genovesi told AFP that most invasive plants in Europe are introduced by selling them to gardens.

“Pampas grass is beautiful, but it spreads very quickly, so once it's out, it's very difficult to contain,” he said.

The plant is “extremely aggressive,” according to the EU-backed LIFE Stop Cortaderia project, warning of its expansion across urban and industrial areas and the decline of native species in the Atlantic coastal areas of France, Spain and Portugal.


The water hyacinth we see here in Lagos has choked waterways around the world.

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The water hyacinth we see here in Lagos has choked waterways around the world.

It has appeared in a European inventory of hundreds of the worst invasive species, an awareness-raising effort to highlight species that cause problems.

Now the International Union for Conservation of Nature is going one step further with a new global classification system called the Environmental Impact Classification of Alien Species.

It has scientific standards to measure the relative threats posed by different harmful species – animals and plants – to help governments prioritize their responses.

The first few species have already been added, but the organization aims to add hundreds, as a complement to the Red List of Threatened Species.

Imperialism and escape

Experts say invasive species are a major driver of global extinction, along with habitat loss, overexploitation, and climate change.

Consider the case of water hyacinth.

Taken from its home in the Amazon by European explorers, the water rose dazzled the imperial court, including France's Napoleon and his plant-loving wife Josephine, with its beautiful, floating blooms.

They took her to Egypt, where she escaped and began a continent-wide conquest.

“In Africa, it creates huge green carpets, impedes navigation, fishing and access to water, destroys the habitat of many fish and also increases evaporation, reducing water reserves,” Genovesi said.

“It also creates a suitable environment for mosquitoes and increases the risk of malaria.”

He said keeping unwanted species in the first place is much easier and cheaper than trying to get rid of them once they take root.


Invasive water hyacinth can block access to waterways.

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Invasive water hyacinth can block access to waterways.

Bad seeds

One major concern – with regard to pampas grass and many other species – is that climate change will increase the range and competitive advantage of invasive species.

Another challenge is international trade in seeds.

The issue was highlighted last year in a bizarre incident in which US authorities sounded the alarm after thousands of Americans reported receiving packages of seeds they had not requested, mostly from China.

Many of the packages were likely part of a “brush scam,” where a seller sends out unsolicited items and posts fake reviews, but that prompted Amazon to announce last September that it would ban imported seeds in the United States.

However, some invaders are more welcome than others.

“You think of the beautiful landscapes of Tuscany, like Cyprus and the poppies and all the grains. They were all introduced, none of them were local, but we love them,” Genovesi said, adding that authorities needed to focus their energies on the speed – the spread and destruction of the varieties.

Even at an IUCN conference, he discovered an insect greenhouse containing invasive plants as well as exotic butterflies.

“We look at that and say: 'Let's hope they don't escape,'” he added.

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