In response to Marlene Condon’s article “Blue Ridge Naturalist: Ecologists Recognizing Value of Alien Plants” in the Crozet Gazette of February 2019:
Non-native invasive plants are a limited group of non-native plants that have been singled out because of special, ecologically harmful properties. They typically seed heavily, spread rapidly, displace native plants, have relatively limited value for native insects and wildlife, and in some instances may be toxic to certain insect and wildlife species. For example, garlic mustard, which prefers the same habitats as some of our best-loved native woodland wildflowers, kills off beneficial soil fungi on which many of these natives depend. In addition, the plant both crowds out native toothwort, the main host plant of the increasingly uncommon West Virginia white butterfly, and fools the butterfly into laying its eggs on the garlic mustard leaves, which are toxic to the butterfly’s caterpillars.
Another example is Japanese knotweed, to which Ms. Condon refers in her article. She criticizes Waynesboro’s Parks and Recreation Department for attempting to eradicate it from the South River greenway. In fact, Japanese knotweed is a perennial herbaceous plant with no woody parts but with large leaves, and in summer it has the same growth form as a dense shrub, completely shading out any other plants in the vicinity. In the fall it completely dies back, leaving bare exposed ground subject to serious erosion throughout the winter, especially along stream-banks, its favorite habitat. In the spring its roots re-sprout so that the plant comes back, forming an ever-expanding area and crowding out more natives. Of course no natives are going to be able to compete under these conditions.
All of us have seen the dense vines festooning trees along I-64 through Charlottesville and along Route 29 South—Porcelain berry, oriental bittersweet, and kudzu, among others. These invasive vines shade the tree crowns, reducing sunlight, which weakens the trees and makes them more vulnerable to ice and wind damage.
The vast majority of non-native plants are not a threat and many are quite useful. Non-natives supply us with the great majority of our fruits and vegetables and lovely garden flowers. It is only a small group of non-natives that become invasive and therefore pose a serious threat to our native species, forests, agricultural lands, and waterways. Because they are a threat, they justify significant efforts to control them and limit their spread. In fact, this is the main message of the essay in Nature that Ms. Condon cites but misinterprets. In their conclusion the authors of the essay write, “Clearly, natural-resource agencies and organizations should base their management plans on sound empirical evidence . . . . [W]e urge conservationists and land managers to organize priorities around whether species are producing benefits or harm to biodiversity, human health, ecological services and economies. . . . [I]t is time for conservationists to focus much more on the functions of species and much less on where they originated.”
Mary Lee Epps
President, Jefferson Chapter, Virginia Native Plant Society