Invasive Species: A Brief Overview

An invasive species is a nonnative (also known as an alien) species that does or is likely to cause economic or environmental harm or harm to human health. The human-mediated spread of species has occurred throughout history. However, as society has become more globalized, opportunities for the spread of nonnative and invasive species have increased (e.g., trade shipments can carry species and introduce them to many different regions of the world). In addition, changing environmental, ecological, and socioeconomic conditions could alter the risk for invasive species introductions in the future.

Invasive species include terrestrial and aquatic plants, animals, and microbes. Their introduction—whether deliberate or unintentional—can pose threats to native animal and plant communities, can lead to ecosystem disruptions, and may contribute to extinctions of native species. Invasive species also can directly cause or transmit threats to human health. The introduction and spread of invasive species also can result in significant economic costs related to damages as well as management, mitigation, and recovery activities. As of 2011, researchers at Cornell University estimated that approximately 50,000 nonnative species have been introduced to the United States, with potential related costs exceeding $100 billion per year. Inherent in any calculation of the costs of invasive species, however, is valuation of economic and societal factors on which expert opinion differs.

Terrestrial and aquatic invasive species can cause environmental degradation and threaten certain U.S. industries, such as agriculture and fisheries. Impacts can include power outages, contamination of agricultural commodities, spread of diseases, increased operating costs, loss of irrigation water, competition with native plants, loss of sport game or endangered species, and ecosystem disturbance. For example, among other impacts,

• Burmese pythons (Python bivitattus) have multiplied in south Florida and prey on native species of reptiles, birds, and mammals;
• zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis) from Eastern Europe have clogged intakes for urban water supplies and nuclear power plants in the Great Lakes and compete with native species;
• citrus greening (Candidatus Liberibacter asiaticus) or Huanglongbing, a citrus plant disease originating from Asia, is spread by disease-infected insects and infects citrus trees, threatening the U.S. citrus industry;
• the light brown apple moth (Epiphyas postvittana), a native pest of Australia, has spread to the United States and is causing damage to a range of commercial fruit and vegetable crops; and
• leafy spurge (Euphorbia esula) has reduced the forage value of western grazing land, resulting in lower overall value to private landowners.

Management

Managing invasive species often involves multiple efforts throughout the stages of invasion (see text box). Prevention of transport and/or introduction is the primary means to avoid a new invasion. When an invasive species is introduced, control efforts may involve eradication where possible and, where not possible, efforts may reduce populations to manageable or tolerable levels. Early detection and rapid response (often by federal agencies) to eradicate invasive populations before they become established can be critical to manage invasive species.

Federal Framework for Invasive Species Management

Federal efforts to control invasive species have included both administrative and legislative actions. For example, several executive orders (EOs) have provided an overarching federal framework to address invasive species. In 1977, President Carter signed EO 11987, which required federal agencies to restrict the introduction of "exotic organisms." In 1999, President Clinton signed EO 13112, which revoked EO 11987, extended federal requirements to address invasive species, and established the interagency National Invasive Species Council (NISC). NISC provides national leadership in addressing invasive species. It is cochaired by the Secretaries of the Interior, Agriculture, and Commerce. In 2016, President Obama signed EO 13751, which expanded the membership of NISC and increased the responsibilities of federal agencies to prevent and respond to invasive species.

Several statutes provide federal agencies authorities to address invasive species in the United States. The current statutory framework includes broad environmental laws and laws that directly address invasive species. For example, the Nonindigenous Aquatic Nuisance Species Act, as amended (16 U.S.C. §§4701 et seq.), and the Noxious Weed Control and Eradication Act of 2004 (7 U.S.C. §§7781 et seq.) are tailored to species' groups or habitats. Broad statutes also can provide authority to address invasive species based on their impacts and include the Endangered Species Act (16 U.S.C. §§1531 et seq.), the Lacey Act (18 U.S.C. §42, 16 U.S.C. §§3371-3378), and the National Environmental Policy Act (42 U.S.C. §§4321 et seq.).

Federal Funding for Invasive Species Activities

Several federal entities share the responsibility to manage invasive species. In FY2017, the U.S. government spent an estimated $3.0 billion across a range of federal agencies and activities in an effort to prevent, control, and eradicate invasive species domestically (Table 1). Activities at the U.S. Department of Agriculture, including those related to agriculture, national forests, and the Animal and Plant Health Inspection Service, accounted for the bulk of federal funding, nearly $1.7 billion (58% of total funds). Activities at the Department of Homeland Security, including border protection and security, accounted for about $0.9 billion (31% of total funding). The remainder of federal funding, about $0.3 billion (about 11% of total funding), covered activities across other departments and agencies, including the Departments of the Interior and Commerce.

For more background, see CRS Report R43258, Invasive Species: Major Laws and the Role of Selected Federal Agencies.