Invasive plants are species intentionally or accidentally introduced by human activity into a region in which they did not evolve and cause harm to natural resources, economic activity or humans. Many introduced species are well known and economically important in agriculture and horticulture, such as wheat, soybeans and tulips. Introduced species, whether plant or animal, often do not become established outside of cultivation and, if they do, they usually have few impacts on natural communities.
Invasive plants, however, propagate wildly and become agricultural pests, infest lawns as weeds, displace native plant species, reduce wildlife habitat and alter ecosystem processes. Across the country and around the world, invasive plants and animals have become one of the most serious threats to native species, natural communities and ecosystem processes. They also exact serious costs from human economies that depend on resources and services provided by healthy ecosystems. Examples include destruction of vast areas of western rangelands, clogging of important waterways and increased costs in maintaining open power line rights-of-way.
Tens of thousands of plant species have been introduced into North America since the beginning of European colonization (Pimentel et al. 2000). Of these introductions, 5,000 species have become naturalized, reproducing outside of cultivation (Morse et al. 1995).
In Virginia, 606 species have been identified as naturalized (Weakley et al. 2012). Of these, 90 species, or 15 percent of naturalized species (3 percent of the total Virginia flora), have been assessed as invasive in natural communities (Heffernan et al. 2014). Economists have estimated that all invasive species — plants, animals and diseases — are responsible for $120 billion in losses each year (Pimentel et al. 2006).
The Virginia Department of Conservation's Division of Natural Heritage and the Virginia Native Plant Society have identified 90 invasive plant species that threaten, or potentially threaten, natural areas, parks and other protected lands in Virginia.
Once thought to be a problem only on farms or in lawns, invasive plants are now recognized as threats to natural areas, parks, forests and other sites in a more or less natural state. Land managers, weed scientists, foresters, ecologists and conservationists are joining together to face this challenge so that native species, natural communities and environmental quality can be protected.
Invasive plants typically exhibit the following characteristics:
An invasive plant infestation is like a slow-motion explosion, which, if left unchecked, may severely alter a site's natural, economic, aesthetic and other cultural values. Management of invasive species can appear to be a complicated and unending task. For this reason, planning and prioritizing are crucial. By articulating clear goals, gathering the best available information and prioritizing actions based on the significance of an infestation's impacts and feasibility of control, land managers can identify how their time, effort and money can most effectively be applied.
Invasive species present a difficult challenge with no quick and easy solutions. Many unknowns exist regarding control methods and their efficacy, in addition to limited budgets for managing invasive plants. Sometimes, the best course of action may be to do nothing.
The entire list of invasive plant species of Virginia is available online as a printable file and as a spreadsheet (.xls). This is an educational list published by the Virginia Department of Conservation & Recreation to inform land managers of potential risks associated with certain plant species known to exhibit invasive behavior in some situations. The list includes the species Invasiveness Rank (I-rank) indicating its degree of invasiveness in Virginia.
Species are ranked as highly invasive, moderately invasive or occasionally invasive. Detailed risk assessments were conducted to determine I-ranks.
The list is not regulatory in nature, and thus does not prohibit the use of the listed plant species. The list identifies species that threaten, or are likely to threaten, forests, wetlands and natural areas. It does not represent a complete list of non-native plant species within the state. New species arrive regularly in Virginia. Some of these species escape cultivation or are introduced accidentally and become naturalized in the landscape. Only a small percentage of new introductions cause harm, and these are considered invasive. New species are evaluated regularly and, if information indicates they are invasive, they are added to the list.
You may also wish to consult local sources of information. For example, the city of Alexandria maintains a list of troublesome non-native plants in the northern Virginia region.
The DCR report, Ranking Invasive Exotic Plant Species in Virginia, provides results of a three-part study of invasive plants. The study included literature review, multivariate analysis and an analysis of data collected from 2,000 vegetation plots located across the state.
You'll need the free Adobe Reader to access this report.
Morse, L.E., J.T. Kartesz, L.S. Kutner. 1995. Native vascular plants. Pages 205-209 in LaRoe, E.T, G.S. Farris, C.E. Puckett, P.D. Doran, M.J. Mac, eds. Our Living Resources: A report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. Washington (DC): US Department of the Interior, National Biological Service.
Pimentel, D., L. Lach, R. Zuniga, and D. Morrison. 2000. Environmental and economic costs of nonindigenous species in the United States. Bioscience 50:1 53-65.
Pimentel, D., R. Zuniga, D. Morrison. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics 52: (2005) 273-288
Weakley, A., C.J. Ludwig, and J.F. Townsend. 2012. The Flora of Virginia. Bland Crowder, ed. Foundation of the Flora of Virginia Project, Inc. Richmond. Fort Worth: Botanical Research Institute of Texas Press.