By JIMMY ROGERS
Courtesy of Judy Fulton
Have you visited Riverfront Park, just behind Main Street in Old Town Laurel? The quiet Patuxent River meanders through the woody ravine that separates Prince George’s and Howard counties. When I first moved to Laurel, I thought the river trail was a perfect place to soak in nature for an hour, especially when escaping the heat of summer. However, as I began to learn about plants in the area, my perspective changed.
In the spring, at any particular point on the path, you will notice lush herbaceous plants carpeting the sandy soil. A closer look at that green carpet reveals it to be a monoculture of lesser celandine (Ficaria verna), an invasive plant from Europe that emerges early and crowds out other low-growing plants. A few feet away from the path, you’ll see tall stalks of what looks like bamboo. This dense thicket, another monoculture, is Japanese knotweed (Reynoutria japonica). It rapidly takes over new areas along riverbanks and secretes chemicals that prevent other plants from growing (a trait known as allelopathy).
Even the most casual visitor will notice the English ivy (Hedera helix) covering a large number of trees. Native vines, like Virginia creeper (Parthenocissus quinquefolia), climb trees as well, but they have evolved to partner with their hosts, rather than killing them like English ivy.
Not long ago the city of Laurel and Laurel for the Patuxent identified an enormous stand of tree of heaven (Ailanthus altissimus) at the western entrance to Riverfront Park. This Chinese tree tends to form dense stands that push out native plants, again using allelopathic chemicals. Plus, it’s the host for the dreaded spotted lanternfly (Lycorma delicatula), an invasive insect which is of great concern to the Maryland agricultural community.
These examples represent a few of the many invasive species I have observed along the Patuxent. I find myself avoiding the park now because the desolation is so complete. These foreign plants cannot feed our insects, they starve (or even poison) our birds, and they choke out the remnants of what was once a vibrant river community.
There is still room to hope. We can learn how all of this happened and then begin to make changes to prevent new invasive incursions.
Many gardeners might describe a plant as invasive because it spreads rapidly. I encourage folks to call these plants aggressive, instead, to avoid conflating a plant’s spreading strategy with its environmental impact. Under then-President Barack Obama, the government defined an invasive species as an organism that “causes or is likely to cause economic or environmental harm, or harm to human, animal, or plant health.” This clarifies the term to focus on the harm it causes, rather than how it behaves in a garden.
You may have noticed the invasive species mentioned above all have an origin outside North America. They evolved in a complex ecosystem full of other organisms competing for dominance. When they were brought here from Europe and Asia, they faced little competition and, if they could survive in the soil and climate, their populations exploded.
European colonists initially introduced plants as either crops, herbs, ornamental plants or unintentional weeds. As a consumer base grew for new plants, the rate of exotic introductions increased dramatically. Today, this behavior continues in almost all Maryland nurseries, which commonly sell English ivy, nandina (Nandina domestica) and burning bush (Euonymus alatus), despite the overwhelming evidence of their impact on wild places. When those species are planted in residential gardens (even in pots), wind- and bird-borne seeds make their way into the forests, reintroducing them again and again.
Invasive plants broadly damage our ecosystems in several ways. In a healthy ecosystem, there is intense competition for every square inch of soil and sun. If a new plant has an unusual advantage over others, it can replace the plants that were there before. More invasive plants means fewer native plants. Additionally, invasive plants often take over large swaths at a time, which reduces overall plant diversity.
Our insects and other herbivores evolved alongside our native plants, adapting to handle the unique toxins created by those plants (secondary metabolites). Newly introduced plants have unfamiliar toxins that our animals cannot deal with, so they leave them alone. Paired with the explosion of the deer population, this has resulted in overgrazed forests where most of the native plants are eaten and the invasive plants can spread without competition.
An uninhabitable forest results from all of this species displacement. Our bees, moths and butterflies can find abundant flowers, but they offer little to no nutrition compared to the flowers that were here even 100 years ago. Many species of insects rely on particular plants; a case in point is the tiny spring beauty bee (Andrena erigeniae) that only feeds on spring beauty flowers (Claytonia virginica); these insect species are at risk of decline and extinction if too many of their host plants lose ground to invasives.
Fortunately, activists in our community have already begun to take action. Laurel for the Patuxent has held vine-cutting workdays for several years. In 2022, they partnered with the city and Howard EcoWorks to clear three-quarterss of an acre of invasive trees, replacing them with a wide variety of native trees.
At the state level, the Maryland Native Plant Coalition has proposed the 2024 Biodiversity and Agriculture Protection Act (HB979/SB915) to ban the sale of invasive plants in Maryland. The bill would combine the state’s current tiered system into a single prohibited list and speed up the assessment process for new additions to that list. It has been co-sponsored by Delegate Linda Foley and Senator Ben Brooks in their respective chambers. Be sure to call or write your state senator and delegates about this important bill (look them up at mdelect.net). For more information on the bill and how you can support it, go to facebook.com/banMDinvasives.
With or without state action, you can make a difference. Plant Invaders of Mid-Atlantic Natural Areas (Swearingen and Fulton, 2022) is a field guide with excellent pictures and instructions for removal of each species. You can get a free digital copy or order it in print at invasive.org/midatlantic/fieldguide/. Check the book before buying plants at a nursery. Identify both the ornamental and weedy plants on your property, so you’ll know if you have invasive species to remove. Change can start in your own garden.
