National Management Plan: Introduction

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[Executive Summary] | [Introduction] | [Survey of Federal Roles &
] | [An Action Plan for the Nation] | [Conclusion] | [Appendices]

The Problem

Invasive species are everywhere. They damage our crops, our industries, the environment and public health. Scientists, academics, leaders of industry and land managers are realizing that invasive species are one of the most serious environmental threats of the 21st century (Mooney and Hobbs 2000).

For centuries people have moved plants, animals, and microbes around the world. Most countries now rely on plants and animals from other regions of the world in order to meet their dietary needs. People in the U.S. also import plants and animals, and their products, for such things as construction materials, ornamental plants, and pets. Organisms that have been moved from their native habitat to a new location (often in a different country) are typically referred to as "non-native," "nonindigenous," "exotic," or "alien" to the new environment. A small percentage cause serious problems in their new environments and are collectively known as "invasive species." Most of U.S. food crops and domesticated animals are non-native species and their beneficial value is obvious - for example managed livestock are examples of non-native species which are not invasive.

An "invasive species" is defined by the Executive Order as a species that is 1) non-native (or alien) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. The Order further provides that a Federal agency may make a determination that the benefits of an action, which may lead to the introduction or spread of an invasive species, clearly outweigh the potential harm caused by the species and take steps to minimize that harm (Executive Order 13112, Appendix 1). This Management Plan is focused on those non-native species that cause or may cause significant negative impacts and do not provide an equivalent benefit to society.

Invasive species have been introduced in a variety of ways. The means and routes by which they are introduced are called invasion "pathways." Some non-native species, intentionally introduced for beneficial purposes, later turn out to be invasive. In the U.S., examples include purple loosestrife, which is sold as an ornamental plant, as well as saltcedar which was introduced for erosion control. Many invasive species are unintentionally introduced; they move as unknown stowaways and "hitchhikers" when people and their products are transported by air, water, rail, or road. Examples of invasive species unintentionally introduced into the U.S. include chestnut blight, the naval shipworm, and imported fire ants. Chestnut blight is one of the most destructive plant diseases ever recorded. This fungus, believed to have come from Asia in imported wood, has forever changed the forest tree composition in the eastern United States. The naval shipworm was introduced into San Francisco Bay via wooden ships in the early part of the 20th century. It excavated the majority of the wood pilings, causing warehouses and loaded freight cars to fall into the Bay. Imported fire ants entered the U.S. with soil removed from ships that transported goods to the U.S. As their name suggests, they cause painful stings. Where they have established in the southern U.S., they can be found in large numbers. They can seriously injure livestock, pets, and humans. They also feed on crops and build large, hard mounds that damage farm and field machinery.

Invasive species can take a heavy economic toll. Researchers at Cornell University estimate that invasive species are costing Americans approximately $137 billion every year (Pimentel et al. 2000). Even controlling a single unwanted invader can carry a price tag in the millions. The United States and Canada are spending $14 million a year just to control the sea lamprey. This species caused the collapse of the lake trout and whitefish fisheries in the Great Lakes (Wilkinson pers. comm.). In 1994, the impacts of invasive plants in the United States were estimated at $13 billion per year (Westbrooks 1998). The list of invaders is long, and the cost of prevention and control is high and going up.

The environmental costs of invasive species can also be staggering. Invasive species typically have high reproductive rates, disperse easily, and can tolerate a wide range of environmental conditions. Often, they lack predators in their new environments. As a result, invasive species may out-compete native species for prey or other resource needs (e.g., breeding sites). They may also prey upon native species, spread pathogens and parasites, or alter the genetic make up of closely related species. Wilcove et al. (1998) estimate that invasive species have contributed to the placement of 35 to 46 percent of the plants and animals on the Federal Endangered Species List. The brown tree snake is a well-known example -- it arrived in the U.S. territory of Guam in the 1940s, probably hidden in military transport planes. It is mildly venomous and an aggressive predator that has driven nine of Guam's eleven native land bird species to extinction.

Invasive plants are estimated to infest 100 million acres in the United States. Every year, they spread across three million additional acres, an area twice the size of Delaware. Every day, up to 4,600 acres of additional Federal public natural areas in the Western continental United States are negatively impacted by invasive plant species (Bureau of Land Management 1996).

Invasive species have also dramatically modified habitats. In some cases, invasive species have altered the ecology of an area to such an extent that the original ecosystem is fundamentally changed. For example, in the U.S., cheatgrass has accelerated the fire cycle in western States by twenty-fold, while saltcedar has altered soil chemistry and impacted native plants and wildlife.

Some invasive species threaten plant, animal, and/or human health. Pathogens and parasites may themselves be invasive species or may be introduced by them (invasive vectors). Bubonic plague is perhaps history's most infamous example of a vectored disease. It was spread by non-native black rats carrying disease-infected fleas. The recently introduced West Nile virus, which is transmitted to humans by mosquitoes that feed on the blood of infected animals, now threatens people and animals in 12 eastern states and the District of Colombia. Cholera and microorganisms that cause certain types of harmful algal blooms are moved in the ballast water carried by large ships.

In many cases, invasive species cause a combination of economic, environmental, and health threats. Typically, studies which document the harm caused by invasive species conclude that the U.S. needs to strengthen its legal authorities and existing programs. A 1993 report by the Office of Technology Assessment, "Harmful Non-indigenous Species in the United States," states that "Federal laws leave both obvious and subtle gaps in the regulation of harmful NIS [invasive species]" (U.S. Congress, OTA 1993). The 1999 report compiled by the National Plant Board for the Animal and Plant Health Inspection Service, "Safeguarding American Plant Resources," notes that the laws giving the agency its authorities "were passed in response to specific plant health crises" and that "overlaps and gaps in this array of statutes often leave the Agency unsure of which authority to apply in any given case…" (National Plant Board 1999). A 1996 publication by The Nature Conservancy notes that the laws that do exist often are not effective or adequately enforced (Stein and Flack 1996). A recent review by Cornell University researchers concludes, "Although [Federal] policies and practices may help reduce accidental and intentional introduction of potentially harmful exotic species [invasive species], there is a long way to go before the resources devoted to the problem are in proportion to the risks" (Pimentel et al. 2000).

Efforts by the U.S. (and all other countries) to prevent the introduction and control the spread of invasive species face a number of challenges:

  • Determining whether a non-native species is invasive requires a context-specific analysis. For example, a species may cause harm in one type of ecosystem, but not others. Because ecosystems are dynamic, their vulnerability to invasion changes over time. Thus, it would be impossible to develop a definitive or complete list of invasive species at the national level. A limited number of invasive species are listed as regulated species under Federal laws governing specific types of species such as noxious weeds, injurious fish or wildlife species, or aquatic nuisance species. States also compile lists of invasive species under their authorities. Although incomplete, this information can be used in setting priorities.

  • Estimates of the number of non-native species that have been introduced into the United States vary widely (from 5,000 to as many as 50,000) (Pimentel et al., 2000). The Office of Technology Assessment report estimates that 10 to 15 percent of introduced species will become established and about 10 percent of established species may become invasive (U.S. Congress, OTA 1993). Many additional species could create problems if introduced. For example, the Animal and Plant Health Inspection Service (APHIS) of the Department of Agriculture has intercepted 7,400 species of plant pests at ports of entry since 1985 that some of which could have become invasive if they entered the United States (APHIS unpublished data).

  • The diversity and number of pathways complicate efforts to prevent introduction and control the spread of invasive species. Green crabs may have hitchhiked in bait shipments, while citrus canker is carried on citrus trees. Many pathways are unknown and pathways have a tendency to change overtime.

  • Once an invasive species becomes established at a new location, it may spread. The pace of establishment and spread depends on numerous factors, including the invasive species' reproduction mechanisms, ability to acclimatize or adapt, whether it has predators or competitors, and what pathways are available for further movement.

In response to the threats posed by invasive species and the challenges to minimizing their spread, the President issued Executive Order 13112 (Order) on Invasive Species, February 3, 1999 (Appendix 1).

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Executive Order 13112 on Invasive Species

In 1997, 500 scientists and resource managers wrote to the Vice President and requested action on invasive species. Their letter stated: "We are losing the war against invasive exotic species, and their economic impacts are soaring. We simply cannot allow this unacceptable degradation of our Nation's public and agricultural lands to continue." An interagency team was launched in response to develop a comprehensive and coordinated strategy for the problem. The team prepared a review of the issue with recommendations, foremost among them was that an executive order be issued providing standards and a framework for ongoing action.

The Order applies to all Federal agency whose actions may affect the status of invasive species and requires agencies to identify such actions and to the extent practicable and permitted by law (1) take actions specified in the Order to address the problem consistent with their authorities and budgetary resources; and (2) not authorize, fund, or carry out actions that it believes are likely to cause or promote the introduction or spread of invasive species in the United States or elsewhere unless, "pursuant to guidelines that it has prescribed, the agency has determined and made public its determination that the benefits of such actions clearly outweigh the potential harm caused by invasive species; and that all feasible and prudent measures to minimize risk of harm will be taken in conjunction with the actions" (Executive Order 13112, Appendix 1). Although the Order applies to all Federal agencies, most of the duties required by the EO are the responsibility of the eight Council members. Given the scope and complexity of the invasive species problem, it is necessary to prioritize actions to deal with the most pressing invasive species problems first.

The Order establishes the National Invasive Species Council (Council), which is chaired by the Secretaries of Agriculture, Commerce, and the Interior and includes the Departments of State, Treasury, Defense, and Transportation and the Environmental Protection Agency. Throughout this document, the term "Invasive Species Council" or "the Council" means the eight member Departments and their constituent agencies, as well as a small staff assigned specifically to the Council. The Order directs the Secretary of the Interior to establish an advisory committee including diverse stakeholders to assist the Council (Advisory Committee), to appoint an executive director with concurrence of the other co-chairs, and to provide necessary staff and administrative support. Current Advisory Committee members are listed in Appendix 4.

The Order directs the Council to provide national leadership and oversight on invasive species and to see that Federal agency activities are coordinated and effective. In addition, the Council has specific responsibilities including: promoting action at local, State, tribal, and ecosystem levels; identifying recommendations for international cooperation; facilitating a coordinated network to document, evaluate, and monitor invasive species' effects; developing a web-based information network on invasive species; developing guidance on invasive species for Federal agencies to use in implementing the National Environmental Policy Act; and preparing this document - the National Invasive Species Management Plan.

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National Invasive Species Management Plan

Requirements of the Order. The Council was directed by the President to release the first edition of the Plan eighteen months after the Order was issued, and to include performance-oriented goals and objectives and specific measures of success for Federal agency efforts concerning invasive species, including objectives and measures for each of the Federal agency and Council duties described above. The Plan is also to identify the personnel, other resources, and additional levels of coordination needed to achieve its goals and objectives. The purpose of the Plan is to provide a blueprint for Federal action (in coordination with State, local, and private programs and international cooperation) to prevent the introduction of invasive species, provide for their control, and minimize their economic, environmental, and human health impacts. The focus of the Plan is on those non-native species that cause or may cause significant negative impacts and do not provide an equivalent benefit to society.

The Order requires that the Plan be developed through a public process and in consultation with Federal agencies and stakeholders. The first edition of the Plan is to include a review of existing and prospective approaches and authorities for preventing the introduction and spread of invasive species, including those for identifying pathways by which invasive species are introduced and for minimizing the risk of introductions via those pathways. Based on this review, the Plan is to identify research needs and recommend measures to minimize the risk of introductions. The Order states that those measures are to provide for a science-based process to evaluate risks associated with introduction and spread of invasive species and a coordinated and systematic risk-based process to identify, monitor, and interdict pathways that may be involved in the introduction of invasive species. If any recommended measures are not authorized under current law, the Council is charged with recommending legislative proposals for new authority.

The Council is required to update the Plan biennially and report on success in achieving its goals and objectives. Within 18 months after measures have been recommended by the Council in any edition of the Plan, each Federal agency whose action is required to implement such measures is required to take the action recommended or provide the Council with an explanation of why the action is not feasible.

The Management Plan: 1st Edition

This first edition of the Plan is the result of extensive consultation with many organizations and individuals with differing interests. Valuable guidance came from the Invasive Species Advisory Committee and members of six working groups made up of both Federal and non-federal experts under the auspices of the Advisory Committee (Appendix 6). The working groups are: (1) international, (2) communication, outreach, and education, (3) policy and regulation, (4) risk analysis and prevention, (5) management, and (6) research, information sharing, documentation, and monitoring. This Plan contains a number of actions recommended by the working groups and discussed in the reports of the groups. These are available for review at the Council's Web site,

The Council also heard from a wide range of organizations and individuals at five public listening sessions held in July 2000 around the country and through numerous written comments. In addition, the Advisory Committee and the Council adopted a set of Guiding Principles, which are located in Appendix 6 of this document. The Council provided a 60-day public comment period on the Draft Management Plan that ended December 1, 2000. As a result, the Council received 181 written comments on the Plan, a few of which were signed by multiple groups or individuals. The majority of the submissions were from non-federal stakeholders. The input from all of these processes is reflected in this edition of the Plan. Although a draft Plan was made available for comment on the Council's Web site in early August of 2000, before the deadline set by the EO, the final version is being issued five months after the EO's deadline, due to extensive revisions made in response to public comment and delays in hiring Council staff.

This first Plan provides a general blueprint for action to deal with the threats posed by invasive species; however, many of the details of the actions called for will require further development in the implementation phase. At that point specific measures of success as well as personnel and other resources needed to achieve the Plan's goals will be described. The action items included in the Plan outline an array of prospective approaches for preventing the introduction and spread of invasive species. The Plan requires agencies to report on their invasive species activities and steps taken to comply with the Order and with the Plan, and provides for an oversight mechanism to ensure agency compliance.

Clearly, many of the actions and goals outlined in the Plan will not succeed unless they are undertaken in cooperation with stakeholders that have extensive programs dealing with invasive species, including other nations, States, tribes, and local governments. The essential and often leading role of State and local efforts and the importance of coordinated Federal and State action are mentioned throughout this edition. It was not within the scope of the Plan to report on or analyze the myriad State and local invasive species programs or plans, although, such an analysis would clearly be useful. As appropriate, coordination with State and local programs and plans will be addressed in the Plan's implementation phase.

Our efforts to minimize the spread of invasive species have begun. Along the way, we will need to more efficiently use our existing resources, as well as obtain additional and sustained resources, both human and financial. This edition of the Plan provides a blueprint for immediate action. To make tangible progress we need to ensure that this Plan is promptly implemented and that future editions follow in a timely manner. We can meet the challenge of invasive species by harnessing the energy, resources and intellect of all concerned.

Invasions in the San Francisco Estuary

The San Francisco Bay/Delta Estuary is an example of how species invasions can change an entire ecosystem. It is possibly the most invaded estuary in the entire world (Cohen and Carlton 1998). More than 230 non-native species have become established in the system, and there are an additional 100-200 species that may be non-native but whose origin cannot yet be determined. The known invasive species cover a wide range of taxonomic groups: 69 percent of the species are invertebrates such as mollusks, crustaceans, and tubeworms; 15 percent are fish and other vertebrates; 12 percent are vascular plants; and 4 percent are microbial organisms. Non-native organisms dominate many estuarine habitats, accounting for 40 to 100 percent of the common species at many sites in the estuary, whether calculated as a percentage of the number of species present, the number of individuals, or of total biomass (Cohen and Carlton 1995). In some areas, it is difficult to find a native organism.

Non-native species introductions have dramatically reduced some native populations, altered habitat structure and energy flows, and caused billions of dollars in economic damage (Cohen and Carlton 1995). The pace of invasion is apparently accelerating. Roughly half of the non-native species have arrived in the last 35 years. Between 1851 and 1960, a new species was established in the estuary every 55 weeks. From 1961 to 1995, the rate was a new species every 14 weeks (Cohen and Carlton 1998).

A number of different pathways have led to new introductions, but there are definite historical patterns to the most significant pathways. Many of the early introductions were organisms transported on the hulls of wooden ships. A number of introductions around the beginning of the 20th century were due to the importation and cultivation of non-native oysters. Even though these oysters did not become established in the estuary, the oyster shipments contained a variety of other species that did. Most recently, the major pathway has been the discharge of ballast water from large ships. In other aquatic systems, additional pathways have been significant. These pathways include the introduction of pathogens and parasites via aquaculture, establishment of ornamental plants, and introduction of species as bait.

Multiple impacts from a single species - Potamocorbula amurensis

In October 1986, three small clams were collected in San Francisco Bay by a college biology class. They were later identified as an Asian species (Potamocorbula amurensis) that had never before been seen on the West Coast. Nine months later, this species had become the most abundant clam in the northern part of the Bay, ultimately reaching densities of nearly 50,000 clams per square meter (Peterson 1996). Other clams were displaced and the biodiversity of bottom-dwelling organisms was reduced (Nichols et al. 1990, Thompson 1998).

This Asian clam is also a highly efficient filter feeder. It has been estimated that clams in the northern portion of the Bay have the capacity to filter the entire water column at least once and possibly more than twice in a single day (Thompson and Luoma 1999). As a result, the clam has virtually eliminated the annual phytoplankton blooms. Phytoplankton are at the base of the food chain and are preyed upon by zooplankton, which in turn are eaten by juvenile fish. There is preliminary evidence that this cascading impact on the food chain has resulted in a reduction in zooplankton populations.

- Andrew Cohen (San Francisco Estuary Institute)

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