Web commerce speeds invasive plant threat

himalayan balsam
Himalayan balsam was introduced as an ornamental and quickly spread throughout the northern hemisphere where it’s considered an invasive plant that displaces native flora in some areas. Photo courtesy Royal Horticultural Society.

Swiss study tracks online sales of potential invaders

Staff Report

Online commerce is accelerating the invasive species threat worldwide, Swiss reasearchers said last week after taking a close look at at the unbridled market for buying and selling plants on the internet.

These days, all it takes is one click to spread potentially invasive plants from continent to continent – and unintentionally encouraging biological invasions, the researchers said, referring to invaders like goldenrod, Himalayan balsam and the Chinese windmill palm — all of which now threaten native biodiversity in the Alpine republic.

The assess the extent of the problem, ETH Zurich researchers monitoried online trades of about two-thirds of the world’s flora on eBay plus nine other online trading platforms for 50 days, tracking which plant species were offered for sale in various countries, and how often.

Software developed for the study helped them match the plants against a list of invasive species maintained by the IUCN. Even though they were only able to monitor the supply side of the equation, the scientists concluded that the huge trading volumes present a significant threat. The study was recently published in Conservation Biology.

“We didn’t expect the global trade in plants that are known to be invasive to be so extensive,” said lead author Franziska Humair.

During the monitoring, the researchers found 2,625 different plant species offered for sale on eBay.  Of all the plants for sale, 510 are known to be invasive in at least one region somewhere in the world. And out of that group, 35 are on the IUCN’s list of the 100 worst invasive species.

Passionfruit, is the invasive plant most often offered for sale. It turns up about 90 times a day, offered by dealers from 17 countries spread over five major geographic regions. This species is highly invasive in the tropics. The second most frequently offered plant is the cornflower Centaurea cyanus, which is put up for sale more than 80 times a day on average and has been classified as an invasive in parts of the U.S.


The plant sellers found in the study were located in 65 countries. Offers to sell invasive species came from 55 of these countries, including Australia. Dealers there offer invasive plants — that can be harmful in other parts of the world — on a grand scale.

“That was unexpected, since the Australians don’t allow you to bring any invasive plants across their borders. But surprisingly, there are apparently no controls in place to make sure potentially harmful plants don’t leave the continent,” said ETH researcher Christoph Kueffer.

“To put it briefly, the vast majority of invasive species can be easily obtained with just a click of the mouse,” Humair said.

Rules governing the trade in these plants are half-heartedly enforced, if at all. And it’s virtually impossible for the dealers themselves to keep track of all the laws and regulations concerning invasive species in different countries. And the threat will grow as new players enter the market. Recently, South Africa started showing up a source country.

“We have no idea whether the plants that are being put on the global market from this corner of world will prove to be invasive species,” Kueffer said. “The only way to contain invasions is by limiting the trade in potential invaders.”

The study shows that it is theoretically possible to continuously monitor this trade in order to spot newly traded species, which could signal future invasions. Many countries already have sets of rules and regulations in place with the goal of curbing the spread of invasive species. Switzerland, for example, has a special ordinance on the release of certain organisms, and the EU countries are in the process of drawing up a list of species that are recognised as invaders across the EU.

“As online trade blossoms, it makes it even more urgent for the authorities to take action or for responsible large commercial nurseries to adjust their product ranges,”  Kueffer concluded.



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