The quiet invasion

Cooper Lake in Woodstock (photo by Dion Ogust)

DEC adds 126 species to banned list; PRISM looks for citizen science volunteers

Pollution, overdevelopment, climate change…the list of degradations to the environment is extensive, posing huge challenges. But perhaps the biggest threat in the Hudson Valley is more insidious. The thick stands of phragmites in marshy areas along the Hudson River, the spindly stalks of garlic mustard and its asterisks of tiny white flowers that pop up everywhere in the yard, the escaped Japanese barberry bush whose thorny tangle of tiny, close-spaced leaves fills the forest like a vegetative mist: These omnipresent monocultures are more than an aesthetic issue. Not only do invasive species crowd out native species, reducing the biodiversity of our forests, river shores, fields and yards, but they also starve the soil of nutrients, seriously undermining the entire ecosystem.

“People say, ‘Why not just let nature take its course?’” said Linda Rohleder, Trail Conference director of land stewardship and coordinator of the Lower Hudson Partnership for Regional Invasive Species Management (PRISM). “Because invasive organisms have not evolved with natives in the environment, the ecosystem has not adapted to invasives,” she explained. “Plants are the basis of the food web. Most insects are adapted to eat three or fewer species of plants, and when you change those species, suddenly there are fewer insects and less food for birds and butterflies. Invading species have a ripple effect on the whole environment. If we let them run their course, it would still be green, but there would be a lot less species.”

Take garlic mustard, for example. “It produces chemicals that inhibit beneficial fungi in the soil that are needed by a lot of wildflowers and tree species for healthy germination in order to thrive,” said Rohleder. While some invasives have some benefits, “The net effect is negative.” For example, birds eat the berries of burning bush and Japanese barberry, thereby spreading the seeds and enabling these plants to invade the forest; but they aren’t as nutritious as the fruits of native plants. Plus, a single invasive species produces food only in a limited period of time, displacing the multiple native plants that produce food throughout the season, she explained.

The problem of invasives means that “Simply buying land [to conserve it] is not enough,” she added. “You need to actively manage it to preserve the native species. Trilliums, for example, don’t survive in areas with a lot of invasives.” When the host plants for certain butterfly species disappear, so do the butterflies. Aquatic invasives such as the red slider turtle and rusty crayfish, which are sold in pet stores and bait shops, displace native fish and invertebrates. The rusty crayfish in particular is a monster species: “It’s very aggressive, eating a lot of organisms and plants at the bottom of streams. .”

The spread of invasives can have other negative repercussions. For example, dense barberry stands “are a perfect habitat for mice, which are vectors for ticks,” said Thomas Lewis, principal of Trillium Invasive Species Management, based in Esopus. “The bushes create an ideal humidity for the ticks to develop,” increasing the risk of Lyme disease.

To raise public awareness and limit the damage, in March the New York State Department of Environmental Conservation (NYS-DEC) issued regulations banning the sale, purchase and transportation of 126 species identified as invasive. The list includes 69 plants, 15 fish, 17 aquatic invertebrates (including several snails and clams), 13 terrestrial invertebrates (insects and land snails), five vertebrates (including the mute swan) and seven species of algae, bacteria and fungi. In addition, 29 species may not be knowingly introduced on or near public lands or natural preserves.  Also banned is the transportation of firewood, which has played a huge role in the spread of the emerald ash borer and the destruction of millions of ash trees.

Among the prohibited plants are garlic mustard, Japanese barberry, Oriental bittersweet, phragmites, Japanese knotweed, multiflora rose, yellow iris, privet and Japanese stiltgrass, while the banned animals include walking catfish, common carp, sea lamprey, Asian earthworms, nutria, Eurasian boar and Asian clam. The insects include pests that are wreaking havoc on shade trees and forests, namely the Asian longhorn beetle, the hemlock wooly adelgid, the emerald ash borer and the Japanese pin sawyer, along with the Africanized honey bee. The complete list can be found at

Some species have a grace period: Nurseries are allowed to sell off their existing stock of Japanese barberry. If you already have barberry, burning bush and other ornamental invasive plants planted in your yard, you won’t be penalized, though “good environmental stewards would look to replace those plants with native plants,” advised Rohleder.

While some invasive plants and animals were introduced by nurseries or pet stores, others arrived by happenstance – as eggs buried in wood pallets, for example, or as packing material, in the case of Japanese stiltgrass. The explosion of international trade has intensified the threat, though Rohleder said that the problem has been on environmentalists’ radar for nearly a century. Only ten percent of species introduced from overseas become invasive, though sometimes it can take decades before it becomes a problem. Japanese barberry, for example, “was a minor player in the forest in the 1970s before it suddenly exploded and had a rapid curve of growth,” she said. “It’s very difficult to determine which species is going to become invasive.”

The plant’s ability to cross-pollinate, its seed production and the places in which it’s planted all play a role, as might other stresses, such as habitat fragmentation or the warming climate. The explosion of the deer population has given invasives a huge boost: Deer only eat native plants, which enables the invasives to gain a foothold and spread. It’s a moving target, and Rohleder said that “More species are starting to be a problem that aren’t on the prohibited list.”

Her organization, the Lower Hudson PRISM, is one of eight in the state formed to monitor invasive species – it received state funding from the DEC in 2013. The task includes establishing an early detection monitoring network and direct eradication and control efforts, as well as educating the public and training citizen volunteers. If you are interested in helping out, visit for training classes and events.

Has there been any success so far? Rohleder said that in the case of the Asian longhorn beetle, efforts to contain it seem to be working, thanks to the aggressive cutting down of stands of infested trees. In the case of the emerald ash borer, the battle is much more difficult, given that “We’re less able to identify the infested trees. It’s been able to move a lot faster than we anticipated.”

Injecting hemlocks with a pesticide protects them from being killed by the hemlock wooly adelgid. “We’re making progress,” Rohleder said. “However, a lot of hemlocks are in steep ravines along streams, where we can’t access them or use a chemical treatment. When they die they’ll affect the water quality.” (The wooly adelgid has already progressed through the lower Hudson Valley and been found in some places in the Catskills, though it hasn’t yet reached the Adirondacks, she noted.) Hemlocks “are a huge component in cooling trout streams and controlling erosion,” noted Lewis.

One of the biggest challenges is complacency from the public. “If we could get everybody to go out and pull [up invasive plants], we could probably take care of the problem,” Rohleder said. “But a lot of people don’t feel it’s worth their time and effort. It’s a political problem.” People continue to plant harmful invasives in their gardens, such as giant hogweed, which can grow ten feet high and has a huge flower. “It was sold by nurseries, and some people still want it in their yard.”

But awareness is increasing. Lewis, who earned a Master’s in Environmental Policy at Bard College and worked as a conservationist for the National Park Service before starting his consultancy, found that there was demand for management of invasive plants.  Lewis gets a lot of calls about getting rid of knotweed and said that the most cost-effective method is to inject the stem with herbicide. “I always try to do the method with the least impact, and the impact to the soil is Number One. I don’t like to pull out plants, which can cause erosion or cause seeds that are buried to germinate.”

If one does remove invasive plants, it’s best to “put them in a clear plastic bag and let them sit in the sun for 30 days, then put it in the trash,” advised Lewis. “If I cut barberry, I just pile it, as long as there are no seeds. You have to be careful where you pile things: Multiflora rose can create roots along the stem. Don’t cut stiltgrass until late summer, “right before it produces seeds. You’ve eliminated production for that year,” he said.

“All these organizations working on this means that people are making a change,” he concluded. “Every little bit you pull out will have contributed to a larger impact. One of the biggest impacts you can have is stopping one of those plants.”


For a complete list of species regulated by the NYS-DEC, visit

To find out more about the Lower Hudson Partnership for Regional Invasive Species Management (PRISM), go to or e-mail Linda Rohleder at [email protected]



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