NARROWSBURG, NY — Non-native plants sometimes behave badly; when they do, it’s no laughing matter. Bad behavior by non-native plants can include insensitivity to the needs of surrounding native plants and animals (as evidenced by blooming earlier and later than its neighbors and by creeping vines that deprive competitors of sunlight), blind ambition (deep, widespread root systems and/or extensive stem and vine systems that crowd out and strangulate plant competitors), and blatant aggression toward all other living entities (bleeding water and nutrients from soil and emitting toxins that compromise or kill plants, animals and even humans). Whatever their modus operandi, the ultimate result is habitat dominance at the expense of other plant and animal species. These villains are known collectively as invasive plant species.
The federal government defines invasive species (both plant and animal varieties) as “a non-native species whose introduction does, or is likely to, cause economic or environmental harm or harm to human, animal or plant health.” [Executive Order 13112, 1999] These species have the ability to displace or eradicate native species, to alter fire regimes, to damage infrastructure and to threaten human livelihoods. Whenever any invasive species is allowed to proliferate unchecked, the consequences are life threatening. Here’s why: The invader reduces ecosystem biodiversity, which in turn, wreaks havoc with food chains and food webs. An illustration would be any invasive plant that chokes out the grasses and low bushes on which small herbivores (rabbits, groundhogs) feed. As small herbivores are displaced because their food sources have dried up, carnivores that feed on them (owls, eagles, foxes, bears and wolves) also are at risk because their food sources are not available. How immediate is this problem? Before salt cedar (an invasive tree known for extracting minerals and water from the soil) began its spread in the mid-20th century, 100 acres of land could support 150 species of wildlife. After salt cedar’s unchecked spread, the same acreage could support four species only.
Where did the invaders come from and how did they get here? They came to North America from all over the world. Some were introduced inadvertently, arriving as seed and spore stowaways. Others were imported deliberately by immigrants seeking to recreate the farms, gardens, products and vistas of their homelands. If all non-native plants were invasive, life as we know it would have ceased before now. Most non-native plants are not invasive and adapt well to their new environments, causing little or no damage to ecosystems. Some co-exist harmoniously for generations, becoming invasive only after climate, growing season or land development conditions alter significantly. Although biologists and botanists admit that it’s difficult to predict with absolute certainty which non-native plants will become invasive, they have identified hallmarks common to most invasive plant species. These include: climatic pre-adaptation; early and frequent production of copious amounts of seed; effective seed dispersal mechanisms; lack of highly specific pollinator requirements; and effective means of vegetative spread. In other words, these plants have developed versatile, highly efficient methods of rapid growth and propagation.
Why has dramatic proliferation of invasive plants gone undetected for so long? Biologist Jamie Myers of the National Park Service in Milanville, PA says simply, “For the most part, the public doesn’t recognize invasive plants when it sees them.” Few Americans today, even those who have long resided in rural areas, are as familiar with local flora as were their agrarian ancestors. And that, Myers says, is what must change before the tide turns in the battle to contain invasive plants. To that end, federal agencies are partnering with private nonprofit conservation organizations to educate Americans about invasive plants, the conditions that foster their proliferation, and the means to manage and eradicate them. The NPS plans to conduct workshops this summer aimed at teaching the public how to identify, manage and eradicate invasive land and aquatic plant species.
Myers stresses that river valleys are potential hotbeds for invasive species because they provide conditions ideal for invasive spread. Water, wind, soil, birds, animals and humans all do their part to disseminate seeds, spores and roots. But, Myers says, humans are by far the worst culprits. Not only are they more numerous than other agents, but they also travel farther and faster and cause more environmental disturbance wherever they go. Disturbed soil is the best medium for invasive plants.
Prevention is the first line of defense in any management program. Invasive species should not be planted knowingly. Surprisingly, some invaders are available from nurseries—Japanese barberry, purple loosestrife and Japanese honeysuckle among them. To guard against deliberate planting, consumers should be able to identify invaders by both name and appearance; additionally, Myers urges consumers to obtain their plants from native plant providers, plant swaps and nurseries that grow their plants from seeds or cuttings.
Methods for management and eradication of invaders vary in accordance with the individual species’ methods of propagation. Options include manual removal (hand weeding), machine removal (mowing, weed whacking), herbicides, grazing (sheep and goats will eat anything edible down to and including roots), burning, and biological attack by natural enemies of the invader (insects, bacteria and fungi). Each method has both advantages and drawbacks, and no one method is safe and effective against all invaders and under all circumstances. There is one more option, to be used either as a last resort and/or a best defense—harvesting. Each plant species, however antisocial its behavior, has attributes that make it useful. Even Japanese knotweed, one of the most tenacious and pervasive invaders, has its uses. The plant’s stalks are used in papermaking. Honey made from its blossoms is considered a delicacy. The plant’s botanical properties are currently being used in the treatment of Lyme Disease. And bakers may find that the plant’s young stalks make a delicious dessert (see Japanese Knotweed Squares recipe).
[Special thanks to Jamie Myers and the NPS for service above and beyond the call of duty. Jamie has considerable experience combating invasive plant species growing along the Upper Delaware, specifically Japanese knotweed and purple loosestrife. Providing guidance and resources to private property owners and community groups alike, Jamie has served on the steering committee for the Delaware River Invasive Plant Partnership and, more recently, on the executive committee for the Catskill Regional Invasive Species Partnership.]