by Courtney Llewellyn
A team of researchers has found that existing regulatory and ethical guidelines are not limiting the widespread introduction of invasive plants. Of the 1,285 identified invasive plants in the continental U.S., 61% – a total of 778, including 20 species that are illegal to grow or sell nationwide – remain for sale in more than 1,300 nurseries, garden centers and via online retailers. They’re being offered as ornamental garden plants. Nearly 40% of the invasive plants now in the U.S. were originally introduced as ornamentals.
The study, “Invaders for sale: the ongoing spread of invasive species by the plant trade industry,” was authored by UMass Amherst’s Evelyn M. Beaury, Madeline Patrick and Bethany A. Bradley. Beaury, a graduate student in organismic and evolutionary biology, said the inspiration behind the study came from her advisor. “This was a topic my advisor thought about for a while – how these invasives got to the U.S. – and a lot of them came through an ornamental pathway,” she said. “That sparked the thought that we’ve known about the issue for a while. How good are we at tackling the problem?”
It turns out, we’re not great at it. In theory, once an ornamental plant can be invasive, commercial sales of that species would stop. Their study found that the current framework for removing invasive plants from plant trade isn’t working. Individual states are generally doing a good job limiting sales of their own regulated plants, but Beaury and her team found major inconsistencies in what’s being regulated across state borders. “Nearly all states had at least one of their regulated plants sold in a neighboring state,” she said. “It’s a tricky situation. The U.S. is big and ecologically diverse, and there are loopholes in certain areas.”
Most states have regulatory lists intended to reduce the spread of high-impact invasive plants. The Federal Noxious Weed Act lists 105 plants considered to be the greatest threats to U.S. natural resources (found at tinyurl.com/e7xxvpaf). The most concerning case of federally designated noxious weed sales, Beaury said, is the availability of cogongrass (Imperata cylindrica), offered by 33 vendors in 17 states. It’s considered one of the world’s most invasive plants. “Plant breeders are marketing a sterile cultivar. But research shows these plants are not completely sterile and can still become invasive,” she noted.
By using an internet search engine and a database of nursery catalogs, the researchers identified invasive plants that continue to be sold. They also recorded the location and distribution of vendors and sales across the lower 48 states, and which sales took place even when federal and/or state regulations prohibited them. The vendors included large online marketplaces like eBay and Amazon, where users can easily ship invasive plants across state borders. “While patchy state regulations definitely contribute to the widespread availability of invasive plants in the U.S., it’s clear we as a public also lack awareness about which plants are invasive and how they spread to new areas,” Beaury said.
“We just started having conversations with growers this spring,” she continued. “We’ve been using state plant boards as our go-between, and we’ve been having more conversations with people on those boards about native species. We’ve found that if people are aware there’s a problem, they care about it. It comes down to the transparency of the issue.”
It also comes down to monetary issues. So many invasives are popular because they’re easy to grow, they’re hardy and they’re pest and pathogen resistant. According to the study, the ornamental plant trade was first identified as a primary source of invasives back in 2001. Today, the most offered invasive species for sale are Chinese silvergrass, common sunflower, butterfly bush and Japanese barberry.
Beaury and her team suggest that consistent regional regulation and coordination – and more educational outreach – is needed to reduce the ongoing propagation of plants known to be invasive.
“I’m optimistic that if a state puts a plant on its list, the industry respects that,” she said. “We’re latching on to the hope of getting more states to link up and create more detailed lists. We also need to prioritize when you need to manage something. It has to be strategic. It’s easier to stop something as it’s growing rather than trying to get rid of it once it’s established. There are success stories out there right now, but we also need to focus on what’s coming next.”
She and her research team have already heard from state regulators that have used their results to follow up with growers selling invasive species. “This is great news, and if we want to continue to protect native ecosystems, regulators and managers need more resources to do so,” she said.
Fortunately, there are several regional resources available now. In the Northeast, there’s the New England Regional Invasive Species and Climate Change Management (RISCC) at risccnetwork.org. In the Pacific Northwest, growers can visit sites.google.com/view/nwriscc. And in the North Central region, there’s earthlab.colorado.edu/our-work/adaptation-science/north-central-riscc. Another useful resource is the Invasive Range Expanders Listing Tool at eddmaps.org/rangeshiftlisting. Beaury noted that one of their next steps is to merge nationwide information for better control.