The Weed Wars: Nantucket Skirmishes with Invasive Plants

As spring finally warms up on Nantucket, you’ll begin to notice some of the shrubs greening up long before anything else. This is a good way to spot invasive non-native weeds in the landscape, such as Morrow’s bush honeysuckle (Lonicera morrowii), autumn olive (Elaeagnus umbellata), and multiflora rose (Rosa multiflora).

One of the classic definitions of a weed is “a plant out of place.” All of these shrubs come from Asia or Europe, so they have traveled far from their native lands to share space with us on Nantucket. Plants like these can create headaches in the garden, or swallow your backyard in enthusiastic greenery if you don’t cut them back each year. If you step out your door, there’s a good chance you will encounter two or three invasive plants before you’ve walked five minutes down the road. In fact, there’s a long list of plants that are invasive in the Northeast, many of which are on Massachusetts’  Prohibited Plants List.  The MA  Guide to Invasive Plants has pictures and other information about most of our problematic species.

How did all of this happen? In recent times, human activity has transplanted plant and animal species all over the globe on a grand and unprecedented scale. Some of them were transplanted intentionally, as lovely additions to someone’s garden, but others were accidentally moved in soil or in weed contaminated seed. While in the past it might have taken a species centuries or millenia to make it to a new island or continent, where it could then set up shop, modern commerce and agriculture have sped up this process alarmingly. These invasive plants aren’t “evil”–they’re just species that are really good at taking over and smothering all in their path. Typical invasive weeds are big seed producers, or are able to send out shoots or runners underground and spread rapidly. Some can do both. Introduced into a new habitat, they do what they do best, and often crowd out the plants that were already well established when they arrived. Areas with disturbed soil or freshly cut brush are particularly vulnerable.

But why are these species a problem when they arrive in a new place, but not in their native land? There are a few theories, but nobody knows for sure. It seems likely that the answers to that question may be slightly different depending on which species you’re asking about. Some may have escaped their insect pests or diseases, while others may have evolved particular traits that make them better adapted to our modern disturbed and fragmented landscape. Some manufacture toxic chemicals in their foliage or have thorns that make them unattractive to native herbivores, and some can produce chemicals in their roots that keep other plants’ seeds from germinating! It’s a jungle out there.

As an island, Nantucket hasn’t suffered the level of invasive plant problems as the mainland, but we definitely have our share. The Nantucket Electronic Field Guide to Invasive Plants produced by the Maria Mitchell Association and the University of Massachusetts Boston can introduce you to this rogue’s gallery of plants. In some ways, the ecological and economic stakes may be higher here on Nantucket–our tiny island owes a lot of its popularity to historic architecture and cobblestoned downtown streets, but also to its picturesque open landscapes. Unlike other coastal towns, more than 45% of Nantucket is designated as conservation land. These open spaces protect vital habitat for many rare plants and wildlife. They also provide extensive views and recreational opportunities, from kayaking in local ponds to hiking, biking, or dog walking with a backdrop of open fields, dunes, forest, and shrubland. In order to maintain these recreational experiences and protect rare native species and their habitat, invasive plants must be managed. A twelve foot tall wall of common reed or knotweed just won’t do.

Local conservation groups have focused their “Weed Wars” on species like common reed (Phragmites australis), purple loosestrife (Lythrum salicaria), Japanese knotweed (Fallopia japonica) and a hybrid knotweed (Fallopia x Bohemica). Managing these species in most cases involves careful use of appropriate herbicides, since these plants have large, well-established root systems that live for many years and spread vigorously. Typically, a permit from the Nantucket Conservation Commission is required to treat these invaders, since they’re mostly found in wetlands and wetland buffers (within 100 feet of a pond or marsh).

Some plants like garlic mustard (Alliaria petiolata) and spotted knapweed (Centaurea stoebe), have started spreading rapidly over the past 5-10 years and have required increasing efforts. These smaller non-woody plants may be treated with hand pulling and placing the removed plants in theantucket Environmental Park digester, which reaches high temperatures that kill weed seeds and roots. It can take up to ten years of diligent removal without allowing the plants to set seed to exhaust the seed bank of species like garlic mustard and knapweed.

Often, people confuse aggressive native plants like scrub oak (Quercus ilicifolia), fox grape (Vitis labrusca), poison ivy (Toxicodendron radicans), or cattail (Typha latifolia) with invasive plants. While these species spread rapidly and we certainly don’t want them everywhere in our yards, they are part of Nantucket’s native ecosystem. These plants support native insects, and by doing so, provide food for birds and other wildlife. And if you’re wondering whether non-native plants can perform the same service, the answer from recent researchers indicates that the answer is no–check out this article on whether invasives can support native moth and butterfly larvae (caterpillars): Can alien plants support generalist insect herbivores? These caterpillars and other insect herbivores are the most important source of food for many nesting birds, and tasty berries produced later in the season won’t feed hungry chicks!

What can you do to help protect the island’s wide open landscapes and rare species from invasive weeds? If you own a home on Nantucket, chances are you live close to a conservation property where an ongoing battle with at least one invasive plant is underway. Learn about the plants in your yard, and when it’s time to work on your landscape, make a plan to replace invasive plants with species native to the island, or with non-invasive alternative plants. Check out this link to the National Arboretum for some great advice. You could replace a single-species hedge with a variety of native shrub species that are appropriate to the site, and these will offer habitat and food for local wildlife. Here’s a good article from the Ecological Landscaping Association on using native shrubs in hedgerows to connect natural areas by providing habitat in developed areas.

You can also participate in educational events and volunteer weed removal days sponsored by the Nantucket Biodiversity Initiative’s Invasive Plant Species Committee. Learn about what you can do in your own yard, or help conservation groups hand pull or dig invasive weeds at sites around the island. Keep an eye out for calendar postings in the local newspapers and their websites.

Please be sure to check out the main Nantucket Conservation Foundation website to learn more about our non-profit, member-supported organization. We work hard to protect the natural habitats and special landscapes of the island, and we can use your help!