When it comes to invasive plants, achieving a state of mindfulness isn’t just about being fully in the present moment.
The all-out focus on managing invasives that are here now may be standard procedure, but when that’s done at the expense of monitoring and prevention efforts, it can exact too high an environmental price, according to invasion ecologists. We must look ahead as well.
This is particularly critical on the larger scale, in conservation. Even for gardeners whose far smaller decisions may impact beyond their backyards, though, scientists urge a shift from being exclusively reactive to taking proactive steps.
Overlook the early warning signs, or disregard invasion risk factors, and pay the price.
“If we’re not proactive, the number of invasions we’re going to be dealing with in the future is only going to be bigger,” said Evelyn M. Beaury, assistant curator at the New York Botanical Garden’s Center for Conservation and Restoration Ecology. “It’s so much easier to do something about an invasion when it’s in an early stage. Your chances of success are much higher.”
The impulse to attempt eradication may not always be the best course of action. With invasive species that are not yet widely established, elimination may indeed be the path to pursue, said both Dr. Beaury and Mason Heberling, who is the associate curator in the Section of Botany at Carnegie Museum of Natural History in Pittsburgh.
Neither one suggests letting established invasives continue to spread unimpeded, but with formidable species that have achieved substantial territory, like Japanese knotweed (Fallopia japonica), “the realistic goal is not full-scale eradication, but containment or mitigation,” Dr. Heberling said. And even that degree of control, he added, can be achieved only through “a continual management effort.”
At the botanical garden, Dr. Beaury said, when elimination of a particular species is unrealistic, the approach is “to suppress invasives to a level where we can still maintain some kind of diversity or function.”
Both Dr. Beaury and Dr. Heberling shared some other insights for better understanding invasives.
Invasives in the Backyard
Invasives aren’t just those plants engulfing our roadsides or strangling trees. Many remain for sale in the nursery industry, and grow in our own backyards as ornamentals.
In 2021, Dr. Beaury published research estimating that 61 percent of the 1,285 plant species identified as invasive in the United States were still available through the nursery trade. That group included 20 that were illegal to grow or sell nationally, and “species that were introduced and recognized as invasive decades ago,” she said in a recent conversation.
So what not to buy? Or what to maybe eliminate from your garden? Search for lists of your state and region’s invasive-plants online and become familiar with them, Dr. Beaury said. In New York, for example, she recommends such lists as the one from Lower Hudson PRISM (the Hudson Partnership for Regional Invasive Species Management). New York Invasive Species Information is another good list for the state.
“What not to buy” is the title of one display in the Carnegie Museum’s extensive exhibit on invasives called “Uprooted: Plants Out of Place,” which opened in March with Dr. Heberling as its content expert. The display suggests foregoing some popular garden plants, like heavenly bamboo (Nandina domestica), butterfly bush (Buddleia davidii), Japanese wisteria (Wisteria floribunda), English ivy (Hedera helix) and periwinkle (Vinca minor), and offers native alternatives.
Warmer temperatures resulting from a changing climate are projected to expand the ranges of many invasives; for the Northeast, for example, scientists are looking to invasions farther south for insights on what’s to come. For species already recognized as invasive in the Mid-Atlantic and Southeast, “the climate is becoming less suitable for their invasion, and our areas are becoming more suitable,” Dr. Beaury said.
She added: “We don’t want to take the problem that’s there and just shift it up here.”
With the Northeast branch of the Regional Invasive Species and Climate Change Management Network, a group of scientists and other stakeholders working to reduce the combined effects of climate change and invasive species, Dr. Beaury helped create a “do not sell” list. It included most of those in the Carnegie display, plus crape myrtle (Lagerstroemia indica), cherry laurel (Prunus laurocerasus), Mahonia (Mahonia bealei), chocolate vine (Akebia quinata) and more plants that have escaped Southern gardens, becoming invasive.
Can we prevent history from repeating itself in another region?
Is It, Or Isn’t It?
Don’t assume that because you haven’t seen a plant self-sow or otherwise spread in your garden that it isn’t invasive.
The paths of invasive-plant movement are many: Seeds may move on the wind, or float downstream where water is present. Construction projects and machinery, or vehicle tires, move plants, too. They may find new homes thanks to a hungry bird that eats a plant’s fruits and moves on. That’s how so many nonnative fruiting shrubs and vines, including barberries (Berberis), privets (Ligustrum), honeysuckles (Lonicera), multiflora rose (Rosa multiflora) and Oriental bittersweet (Celastrus orbiculatus), have become so widespread.
How far from your garden can something spread and affect surrounding natural areas, and how long will that take? “We have tried to approximate the distance, but that connectivity is one of the big knowledge gaps in invasion ecology,” Dr. Beaury said.
There is much to learn, but the presence of so many invasives in gardens, and such notable examples as Japanese barberry (Berberis thunbergii) and burning bush (Euonymus alatus) — garden escapes that have attained widespread invasive status — suggest the effect is very real.
Remember: Invasive plants found their way to their new homelands in the first place as a result of human activity, whether intentional or otherwise.
People moved the plants. That’s a resounding message behind the Carnegie exhibit, which recounts the histories of known invasives to get at why certain plants with particular traits eventually succeeded — traits that give experts insight into how invasion works, and what to watch for.
One featured plant is multiflora rose, introduced from Asia in the 19th century as an ornamental, and used in erosion control, as a living fence, and as a rootstock for grafting other roses.
Knotweed, a research focus of Dr. Heberling’s, likewise arrived in the 19th century, also intended for ornamental and erosion-control use. In its native Japan, it is valued for culinary and medicinal uses.
Another widespread invasive introduced for ornamental use around the same time, and “a big issue in NYBG’s forests,” said Dr. Beaury, is lesser celandine (Ficaria verna), native to Europe, and parts of Africa and Asia.
“It emerges early in the spring and outcompetes other spring ephemerals for space, reducing the diversity of wildflowers available then to pollinators,” she said.
Garlic mustard (Alliaria petiolata), a biennial that is all too familiar to many gardeners, was introduced from Europe in the 19th century as a culinary and medicinal herb.
Unlike the others, stiltgrass (Microstegium vimineum) was an accidental introduction, thought to have arrived in the early 20th century as a packing material with ceramic shipments from China. Though it is an annual grass, it has displaced natives and claimed extensive territory, thanks to its prodigious seed production.
Going With Native Species
The easiest way to confidently avoid harm is to select native species to garden with.
“Switching to having a native-dominated garden, at least 50 to 70 percent native species in your garden, just reduces the invasion risk massively,” Dr. Beaury said. “It’s a lot easier to select the plants that we know have benefits, rather than trying to avoid or parse out the species that could be harmful.”
“Native” can mean so at multiple scales, she said. Local natives are the obvious choice, but not the only one in our changing times. Invasives aren’t the only plants being pressured by the climate to seek new homes.
“We’ve been advocating for folks to start thinking about species that are native regionally or eco-regionally, because there’s a lot of these plants that are also needing to migrate with climate change,” Dr. Beaury said. “Your garden can sort of serve as that steppingstone into natural areas for a lot of native plants that may not be able to migrate fast enough without some help.”
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