BY FRED SEITZ — Since 2005, the Anacostia Watershed Society and more than 250 volunteer “weed warriors” have been working to remove invasive species of plants in Magruder Park and other nearby areas. Their efforts are paying off; coordinator Marc Imlay estimates that approximately 80 percent of the park’s bush honeysuckle and 95 percent of its English ivy have been removed. The garlic mustard is, he says, currently controlled. The battle continues with other top offenders, like multiflora rose and bamboo.
That has cleared the way for several attractive natives, including mayapples (a popular food for many animals), trout lilies (another edible), jewelweed (the native species of impatiens and a possible native source for reducing poison ivy irritation), jack-in-the-pulpit and skunk cabbage (both used by Native Americans).
Invasive plant species – and their removal – have been the subject of considerable discussion for at least a decade. The determination of the negative or positive aspects of an invasive plant is sometimes quite subjective. The issue gained national attention in the ’90s, when President Clinton created the National Invasive Species Council. The Bureau of Land Management and others have cited the negative impact of invasive plants on grazing lands for cattle and other domesticated animals. Douglas Tallamy, in his eloquent work Bringing Nature Home, explains how invasive plants may beget invasive insects and animals, posing a serious threat to our ecosystem.
Higher up the food chain, snakeheads and zebra mussels have been the focus of recent invasive-species discussions. The former have been cited as threats to popular game fish such as bass – but it is seldom mentioned that bass themselves were introduced to many local water systems. While zebra mussels are blamed for clogging power plant filters, they do clean the water of several harmful pollutants.
Many of the “invader plants” were introduced as positive environmental interventions; both multiflora rose and the infamous kudzu were brought in to control erosion. Others, such as bamboo and English ivy, were introduced for their perceived attractiveness to gardeners and landscapers. Some decorative fruit-bearing shrubs provide food for birds (who spread the seeds), but in turn alter the chemistry of the soil, putting native plants at risk and possibly jeopardizing cover and nesting sites for the birds.
When some of these invasive plants were introduced, their ability to edge out native plant species and their possible negative impact on wildlife was unknown. But it turns out that one of the most pervasive invaders, English ivy, not only displaces native ground covers but attaches itself to trees and can kill them.
Several local nurseries that stock native plants also sell English ivy and other invasive species, due to their popularity with some gardeners and landscapers. However, one of the strongest arguments for using native species is their relatively low maintenance. They also supply food for native wildlife and pollinators.
AWS continues to sponsor invasive removals, some coordinated with similar activities sponsored by the National Wildlife Federation. The State of Maryland’s Department of Natural Resources also has periodic invasive removal efforts in several state parks. The Fish and Wildlife Service has published an excellent guide for local native plants that can provide good wildlife habitat and aesthetic alternatives to many popular ornamental, non-native species.