Invasive species are a significant threat to many native habitats and species of the United States and a significant cost to agriculture, forestry, and recreation. The term "invasive species" can refer to introduced or naturalized species, feral species, or introduced diseases. Some species, such as the dandelion, while non-native, do not cause significant economic or ecologic damage and are not widely considered as invasive. Overall, it is estimated that 50,000 non-native species have been introduced to the United States, including livestock, crops, pets, and other non-invasive species. Economic damages associated with invasive species' effects and control costs are estimated at $120 billion per year.
Notable invasive species
For a more complete list of invasive species, see List of invasive species in North America
Economic impacts of invasive species
The economic impacts of invasive species can be difficult to estimate, especially when an invasive species does not affect economically important native species. This is due in part to the difficulty in determining the non-use value of native habitats damaged by invasive species, and in part to incomplete knowledge of the effects of all of the invasive species present in the U.S. Estimates for the damages caused by well-known species can vary as well. The Office of Technology Assessment (OTA) has estimated zebra mussel economic effects at $300,000 a year, while an ACoE study put the number at $1 billion. Estimates of total yearly costs due to invasive species range from $1.1 billion per year to $137 billion per year
In 1993, the OTA estimated that a total of $100 million is invested annually in invasive species aquatic weed control in the US. Introduced rats cause more than $19 billion per year in damages, exotic fish cause up to $5.4 billion annually, and the total costs of introduced weeds are estimated at around $27 billion annually. The total damage to the U.S. native bird population due to invasive species is approximately $17 billion per year. Approximately $2.1 billion in forest products are lost each year to invasive plant pathogens in the United States, and a conservative estimate of the losses to U.S. livestock from exotic microbes and parasites was $9 billion per year in 2001.
Government polices and management efforts
The federal government has historically promoted the introduction and widespread distribution of species that would become invasive, including multiflora rose, kudzu, and others for numerous reasons. Before the 20th century, numerous species were imported and released without government oversight, such as the gypsy moth and house sparrow. Over 50% of flora recognized as invasive or noxious weeds were deliberately introduced to the United States, by either government policy or individuals. Current government policy can be broadly separated into two categories: preventing entry of a potential invasive species and controlling the spread of species already present. This is carried out by different government agencies, depending on what types of damage a species can cause.
Regulations designed to prevent entry of invasive species
The Lacey Act of 1900, originally designed to protect game wildlife, its role has increased to prohibit parties from bringing non-native species that have the potential to become invasive into the United States. The Lacey Act gives the FWS the power to list a species as "injurious" and regulate or prohibit its entry into the U.S. The Alien Species Prevention and Enforcement Act of 1992 makes it illegal to transport a plant or animal deemed injurious into the United States through the mail. The FWS concerns itself mostly with the invasive species likely to threaten sensitive habitats or endangered species.
The USDA is also involved in preventing the introduction of invasive species, largely through the Animal and Plant Health Inspection Service, or APHIS. APHIS was originally tasked with preventing damage to agriculture and forestry from alien species, pests, or diseases, but has had its mission expanded to include preventing invasive species spread as well. This includes identifying potential pests and diseases, assisting in international and domestic eradication efforts, and the Smuggling Interdiction and Trade Compliance Program, designed initially to deal with illegally imported produce, but now tasked with preventing the entry of exotic pests, diseases, and potentially invasive species. APHIS also enforces bans against interstate transport of pests, diseases, and species listed as injurious, noxious weeds, or nuisance species. An example of the USDA banning imports is the ban on fresh mangosteen fruit due to concerns about fruit flies from southeast Asia. This ban originally allowed only frozen or canned fruit, but now allows for fresh irradiated fruit to enter.
Reducing the spread of invasive species
Many invasive species are spread inadvertently by human activities, such as seeds stuck to clothing or mud transporting firewood, or through ballast water. The government has instituted several different policies related to different pathways the invasive species may be spread. For example, quarantines on a federal and state level exist for firewood across the Eastern United States in an attempt to halt the spread of the emerald ash borer, gypsy moth, oak wilt, and others. Transporting firewood out of quarantine zones can result in a fine of up to $1,000,000 and 25 years in jail, but punishments are usually much lower.
The techniques available for controlling the spread of invasive species can be broadly defined into 6 categories:
- Cultural practices
- Controlled burns and timbering. An example of this in action is the use of prescribed burns in the Everglades to control Melaleuca quinquenervia trees. The burns destroy Melaleuca, but not native species which have adapted to wildfires, which were common, but are now suppressed
- Interference with dispersal
- May include fencing, reducing accidental seed transport, and the construction of barriers, such as the electric barrier on the Chicago Sanitary & Ship Canal, discussed below.
- Mechanical removal
- Includes mowing, harvesting, manual removal, trapping, & culling. Many invasive plants, such as garlic mustard, can regrow quickly after mowing and must be removed by the roots or chemically.
- Chemical control
- May include the use of any approved pesticide or herbicide, or vaccines to control invasive diseases. Sea lampreys in the Great Lakes have had their numbers significantly reduced by a lampricide that kills larvae, which hatch in streams, before they can enter the lakes. The lampricide is responsible for reducing the sea lamprey population in the Great Lakes from over 3 million in the 1950s to around 450,000 today, and with potentially rescuing several Great Lakes fisheries.
- Biological control
- Can involve the release of specific predators/herbivores, parasites, or diseases designed to control an invasive species without damaging native ones. One example of this is the city of Chattanooga's use of goats to control kudzu growing on mountain ridges. The goats, guarded from predators by llamas, eat the vine often enough to slowly starve the roots, killing the plant. This method is much cheaper than the repeated mowing or herbicidal spraying that would otherwise be necessary. Goats reach areas which are inaccessible to machines and have multichambered stomachs which coupled with their grazing technique mean that goats leave few seeds behind to sprout again.
- Interference with reproduction
- This can include the release of mating-disrupting pheromones or the release of sterile males. Field tests are underway to study the control of sea lampreys in the Great Lakes by the use of pheromone-baited traps in streams, in addition to current chemical controls. When female sea lampreys return to the stream to breed, they are drawn to the traps and captured, preventing reproduction from occurring.
An integrated pest management (IPM) approach, as defined by the National Invasive Species Council, uses scientific data and population monitoring to help determine the most efficient control strategy, which is usually a combination of several of the methods listed above. Agencies are encouraged to use an adaptive management strategy, involving regular reviews on the efficiency of their policies and conduct research into better methods.
Invasive species control is not overseen by one government agency. Rather, different invasive species are controlled by different agencies. For example, policies aimed at controlling the emerald ash borer are undertaken by the USDA, because National Forests, the body coordinating emerald ash borer control efforts, are within the USDA. The National Invasive Species Council was created by executive order in 1999 and charged with promoting efficiency and coordination between the numerous federal invasive species prevention and control policies. The NISC is co-chaired by the secretaries of the three federal departments that are charged with invasive species control: Interior, Agriculture, and Commerce. Many state efforts use a similar council model to coordinate agencies within a state.
Education and outreach
Many of the policies used to contain invasive species, such as firewood transport bans or cleaning shoes and clothes after hiking are effective only when the general public knows of their existence and importance. Because of this numerous programs to inform the public about invasive species. This includes placing signs at boat ramps, campsites, state borders, hiking trails, and numerous other locations as reminders of policies and potential fines associated with breaking policies. There are also numerous government programs aimed at educating children, promoting volunteer efforts at removal, and the many ways citizens can prevent the spread of invasive species
Invasive species by area
Current efforts in the Great Lakes ecoregion focus on measures that prevent the introduction of invasive species. As a major transport area, a number of invasive species have already been established within the Great Lakes. In 1998, the United States Coast Guard, in accordance with the National Invasive Species Act of 1996, established a set of voluntary ballast water management program. In 2004 this voluntary program became mandatory for every ship entering US controlled waters. Current measures are among the most stringent in the world and require ships entering from outside the Exclusive Economic Zone to flush ballast water in open seas or retain their ballast water for the length of their stay in the Great Lakes. Failure to comply with the US Coast Guards regulations can result in a class C felony.
Another preventative measure in the Great Lakes region is the presence of an electrified barrier in the Chicago Sanitary and Ship Canal. The barrier is meant to keep Asian carp from reaching Lake Michigan and the other Great Lakes. On December 2, 2010, Michigan, Ohio, Pennsylvania and Wisconsin were denied their request to force the closing the Canal by Judge Robert Dow of the United States District Court for Northern District of Illinois. The closing of the Canal would have once again permanently separated Lake Michigan and the Mississippi river system. States argued that the canal, and the Asian carp in it, posed a risk to $7 billion worth of industry. Currently the electric barrier is the only preventative measure and some question its effectiveness, particularly following the discovery of Asian carp DNA past the barrier.
Rocky Mountain Region
The USDA Rocky Mountain Research Station (RMRS) has a specific Invasive Species Working Group to do the research about invasive species in Rocky Mountain region. The Invasive Species Working Group focuses on four key areas: (1) prediction and prevention, (2) early detection and rapid response, (3) control and management, and (4) restoration and rehabilitation. Specific approaches include prioritizing of invasive species problems, increased collaboration among agencies regarding those problems, and accountability for the responsible use of the limited resources available for invasive control.
Invasive species of particular concern in the Rocky Mountain region include: cheatgrass; leafy spurge; tansy ragwort; spotted knapweed; bufflegrass; saltcedar; white pine blister rust; armillaria root rot; introduced trout species; golden algae; spruce aphid; and banded elm bark beetle.
Already stressed by water management and damming, the Colorado River of Western United States is losing its big-river fish community to combined effects of predation and competition by introduced non-native fishes. This fish community includes four large fishes that are listed as endangered by the U.S. Fish and Wildlife Service. One of these, the Colorado pikeminnow (AKA white or Colorado river salmon, Ptychocheilus lucius) is the largest minnow native to North America, and it is well known for its spectacular fresh water spawning migrations and homing ability. Despite a massive recovery effort, its numbers decline. Hampered by a loss of about 80% of its habitat, the young of this once abundant fish is overwhelmed in its nursery habitat by invasive small fishes (such as red shiner and fathead minnow), whose numbers are as high as 90% of the standing stocks. Its juveniles and adults now must also compete with and are preyed upon by introduced northern pike, channel and flathead catfishes, large and smallmouth basses, common carp, and other fishes.
Invasive species by state
California has created a policy system towards invasive species, including Invasive Species Council of California (ISCC), California Invasive Species Advisory Committee (CISAC) and California Invasive Plant Council (Cal-IPC), a non-profit organization. The ISCC represents the highest level of leadership and authority in state government regarding invasive species. The ISCC is an inter-agency council that helps to coordinate and ensure complementary, cost-efficient, environmentally sound and effective state activities regarding invasive species. CISAC advises the ISCC, and created the California list of invasive species California has many diverse ecoregions, and numerous endemic species that are at risk from invasive species.
Invasive species in Florida currently make up more than 26% of the animal population and a full one third of the flora population. In 1994, the Everglades Forever Act of 1994 was passed to help in controlling Florida's water supply, recreation areas, and diverse flora and fauna. In addition to control and prevention measures the act also calls for efforts to monitor the distribution of known invasive species
One invasive species occurring in the Everglades that can have serious consequences is the Burmese python. Between 2000 and 2010, approximately 1,300 of the snakes were removed from the Everglades. Currently the National Park Service is researching control measures for the Burmese python in order to limit the species effects on the delicate Everglades ecosystem
Also Rhesus Monkeys were introduced to Florida.
In Hawaii measures to prevent the introduction and spread of invasive species are coordinated by the Hawaii Invasive Species Council. Currently the council is broken into five committees which focus on different areas of invasive species control. These focus areas are (1) prevention (2) management of established pests (3) increased public awareness (4) research and technology and (5) monetary resources.
Currently, Hawaii requires inspection of any and all plant, animal and microorganism transports. This includes transports from the mainland in addition to transports occurring between islands. Travelers are required to fill out a declaration form for each journey. Failure to declare these transports can result in up to one year imprisonment or a $250,000 fine. Many potential invasives or carriers for invasives require permits and quarantine periods before entry to the state is allowed.
In addition, there are other preventative measures such as a hotline for reporting sightings of known potential invaders like the brown tree snake.
The Idaho Department of Agriculture (U.S.) has around 300 introduced or exotic species listed with 36 classified as noxious weeds (invasive species). The legal designation of noxious weed for a plant species can use these four criteria:
- It is present in but not native to state-province-ecosystem.
- It is potentially more harmful than beneficial to that area.
- Its management, control, or eradication is economically and physically feasible.
- The potential adverse impact of it exceeds the cost of its control.
Some of the plants on Idaho's noxious weed list that are harmful or poisonous are:
- Leafy spurge: native to Eurasia. It has a milky latex in all its parts that can produce blisters and dermatitis in humans, cattle, and horses and may cause permanent blindness if rubbed into an eye.
- Poison hemlock: native to Europe. It contains highly poisonous alkaloids toxic to all classes of domesticated grazing animals.
- Russian knapweed: native to the Caucasus in southern Russia and Asia. It causes chewing disease in horses.
- Tansy ragwort: native to Eurasia. All parts are poisonous, it causes liver damage to cattle and horses, while it affects sheep to a lesser extent.
- Toothed spurge: native to the Great Plains region. A milky latex exists in all parts of the plant that can produce blisters and dermatitis in humans, cattle, and horses. It may cause permanent blindness if rubbed into the eye.
- Yellow starthistle: native to the Mediterranean basin area and Asia. It causes death and chewing disease in horses.
- Yellow toadflax: native to Europe. It contains a poisonous glucoside that may be harmful to livestock.
The Tsunami fish is an invasive species that washed up on the shores of Washington following the 2011 TÅhoku earthquake and tsunami.
- List of invasive species in North America
- List of invasive species in the Mid-Atlantic region of the United States
- Environmental issues in the United States
- Coates, Peter (2007). American Perceptions of Immigrant and Invasive Species: Strangers on the Land. University of California Press. p.Â 266. ISBNÂ 0-520-24930-5.Â
- Invasive Plant Atlas of the United States
- Center for Invasive Species and Ecosystem Health at the University of Georgia
- Center for Invasive Species Research at the University of California, Riverside
- Invasive Species Specialist Group - global invasive species database
- Invasive Species Research at the Rocky Mountain Research Station
- National Invasive Species Information Center, National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for invasive species.
- Weeds at the Bureau of Land Management
- The Nature Conservancy's Great Lakes Project- Aquatic Invasive Species
- Invasive and Noxious Weeds the Department of Agriculture (USDA)
- Noxious Weed Program at the Department of Agriculture
- By state
- Montana's Weed Awareness Program: Pulling Together
- Noxious Weed Photos, King County, Washington State
- cal-ipc: "Noxious Weed definitions"