Invasive species are a crucial threat to many native habitats and species of the United States and a significant cost to agriculture, forestry, and recreation. An invasive species refers to an organism that is not native to a specific region, this poses significant economic and environmental threats to its new habitat.[1] The term "invasive species" can also refer to feral species or introduced diseases. Some introduced species, such as the dandelion, do not cause significant economic or ecologic damage and are not widely considered as invasive. Economic damages associated with invasive species' effects and control costs are estimated at $120 billion per year.[2]
The main geomorphological impacts of invasive plants include bioconstruction and bioprotection.
| Picture | Common Name | Species Name | Introduced | Control Measures | Notes |
|---|---|---|---|---|---|
| Pueraria lobata | Southern U.S. | Known as "the vine that ate the South", forms dense monocultures that outcompete native ground cover and forest trees. Can grow up to one foot per day. For more details, see Kudzu in the United States. | |||
| Kali tragus | Throughout North America | Managed grazing | Introduced through imported flaxseed from Russia that was contaminated with Kali seeds. Although invasive, it is used in Westerns to symbolize frontier areas of the United States. | ||
| Ligustrum spp. | Southeastern U.S. | Mechanical removal, herbicides | Highly invasive in urban areas and forested area of the southeastern U.S. | ||
| Dreissena polymorpha | Great Lakes, U.S. waterways & lakes | Ballast water transport bans, manual removal from clogged pipes | Initially spread by ballast tanks of oceangoing vessels on the Great Lakes, now spread lake-to-lake by trailer-drawn boats. May be a source of avian botulism in the Great Lakes region. | ||
| Sturnus vulgaris | Contiguous United States | Hunting, trapping | Introduced in 19th century as part of an effort to bring all species mentioned in Shakespeare's works to the United States. 100 birds released in Central Park have spread all over the mainland U.S. | ||
| Boiga irregularis | Dog-sniffing of incoming ships, paracetamol as poison | Has reached densities on Guam of up to 100 snakes per hectare, caused extinction on Guam of at least 12 bird species. | |||
| Python bivittatus | Hunting season created | Introduced by hurricane damage to breeding facilities. | |||
| Apis mellifera hybrid | Southwestern U.S. | Cold weather has limited spread | Hybrid of African and European honeybees created in Brazil in the 1950s, described as "killer bees." While individually no more venomous than European honeybees, attacks are particularly violent and usually involve large numbers of stings, which can be cumulatively fatal to animals and people. | ||
| Mississippi River and tributaries | Rotenone poison, electric barriers | Have the habit of jumping out of the water, which can injure boaters. Introduced to eat algae in fish ponds in Southern U.S., escaped during flood events. | |||
| Agrilus planipennis | Eastern U.S. | Culling infected stands, bans on firewood transport | Threatens to severely reduce or eliminate the ash lumber industry of U.S., worth an estimated value of $25.1 billion per year | ||
| Adelges tsugae | Eastern U.S. | Insecticide treatment | Could kill most eastern hemlocks in the U.S. within the next decade | ||
| Rosa multiflora | Eastern U.S. | Manual removal, herbicides[3] | Introduced for erosion control and promoted as a "living fence" to attract wildlife, now competes with native understory plants | ||
| Bythotrephes longimanus | Ballast water transport bans | Competes with native fish for prey, spines prevent many native fish from eating it as prey | |||
| Channa argus | Possession of a live specimen is illegal in many U.S. states.[4] | Snakeheads can become invasive species and cause ecological damage because they are apex predators.[5] | |||
| Lissachatina fulica | Pest control | This invasive species was smuggled into Florida from Africa. Since they need calcium to build their shells, they attach themselves to concrete, which in many cases is house foundations, weakening house structures. | |||
| Pterois | Southern U.S. | Lionfish derbies[6] | Lionfish compete for food with native fish species. They have no natural predators because of their venomous spines.[7] | ||
| Rhinella marina | Pest control | They pose as threats to animals since they are toxic. | |||
| Crocodylus niloticus | Florida | Unknown | Several specimens have been recently captured in South Florida, though no signs have been found that the population is reproducing in the wild.[8] [9] | ||
| Orconectes rusticus | Across the states | The larger size and aggressive nature of rusty crayfish that have been introduced to a body of water makes it harder for them to be preyed upon by native species of fish, which are not accustomed to crayfish fighting back against them.[10] | |||
| Lycorma delicatula | Northeastern and Mid-Atlantic U.S. | Pest control | Highly invasive, with potential to spread across much of the Midwest and Western U.S.[11] | ||
| Popillia japonica | Northeastern, Southern and Midwestern U.S. | Poison, diseases, parasites.[12] | Pest of roughly 300 species of plants, rapid spread.[13] | ||
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 partly because of the difficulty in determining the non-use value of native habitats damaged by invasive species and 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 per year, while a United States Army Corps of Engineers study put the number at $1 billion per year. The United States government spends an estimated $1 billion annually to recover from the invasive Formosan termite, investing $1 billion of this budget in areas surrounding New Orleans, a major port city.[14] Estimates of total yearly costs controlling invasive species range from $1.1 billion to $137 billion per year.[15]
In 1993, the OTA estimated that a total of $100 million is invested annually in invasive species aquatic weed control in the U.S.[16] Introduced rats cause more than $19 billion per year in damages,[17] exotic fish cause up to $5.4 billion annually, and the total costs of introduced weeds are estimated at around $27 billion annually.[18] The total damage to the native bird population from invasive species is approximately $17 billion per year. Approximately $2.1 billion in forest products are lost each year to invasive plant pathogens, and a conservative estimate of the losses to livestock from exotic microbes and parasites was $9 billion per year in 2001.[19]
The federal government has historically promoted the introduction and widespread distribution of species that became 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.[20] 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.
The Lacey Act of 1900 was originally designed to protect game wildlife. Its role has increased to prohibit parties from bringing non-native species into the country that have the potential to become invasive. The Lacey Act gives the United States Fish and Wildlife Service (FWS) the power to list a species as "injurious" and regulate or prohibit its entry into the U.S.[21] The Alien Species Prevention and Enforcement Act of 1992 makes it illegal to transport through the mail a plant or animal deemed injurious. The FWS concerns itself mostly with the invasive species likely to threaten sensitive habitats or endangered species.
The United States Department of Agriculture (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.[22] 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.[23] 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 because of 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.[24]
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 million and 25 years in jail, but punishments are usually much lower.[25]
The techniques available for controlling the spread of invasive species can be broadly defined into six categories:[26]
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.[26]
Invasive species control is not overseen by a single government agency. For example, eight agencies (divisions) of the USDA work on invasive species issues, including the Agricultural Research Service, Animal and Plant Health Inspection Service, Cooperative State Research, Education, and Extension Service, Economic Research Service, Farm Service Agency, Foreign Agricultural Service, United States Forest Service, and the Natural Resources Conservation Service.[31] 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's purview.[32] The National Invasive Species Council (NISC) 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: Department of Interior, Department of Commerce, and the USDA.[33] Many state efforts use a similar council model to coordinate state agencies.
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 have been implemented 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,[34] as well as promoting volunteer efforts at removal and the many ways citizens can prevent the spread of invasive species.[35]
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 voluntary ballast water management program. In 2004 this voluntary program became mandatory for every ship entering U.S.-controlled waters.[36] 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.[37] [38] Failure to comply with the U.S. Coast Guard’s regulations can result in a class C felony.[39]
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 of the canal by the United States district court.[40] [41] The closing of the canal would have once again 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.[42] 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.[43] The discovery of DNA of Asian carp could be linked to live bait used around the Great Lakes region. The method for identifying the DNA is called environmental DNA (eDNA) surveillance. This method uses DNA that is left in the environment to identify species in low abundances.
In June 2022,[44] the Illinois Department of Natural resources announced a campaign to rebrand Asian carp as Copi.[45] The Copi renaming is a part of a Federal and state initiative to get the public to eat the invasive fish,[46] decrease its numbers in Midwestern waterways,[47] and prevent its introduction to the Great Lakes.[48]
The federal United States Environmental Protection Agency—the Great Lakes Restoration Initiative[49] - is funding the Copi rebrand of Asian carp.[48]
Copi is available in restaurants in Illinois, Arizona and Washington, D.C.; in 7 fish markets in Illinois and Tennessee; and by 7 fish distributors in Illinois, Michigan, New York, Ohio, Maryland and Wisconsin.[76] Success of the Copi rebrand of the invasive fish will be measured using pounds of removal as the key metric. Removal was projected to total 6,000,000 lbs at launch of the Copi rebrand, and increase to 12,000,000 in the first year following. Removal at 2 months from launch exceeded 10,000,000 lbs, on pace to beat year 1 projections.[77]
The USDA Rocky Mountain Research Station has a specific Invasive Species Working Group[50] to do the research about invasive species in Rocky Mountain region. The Invasive Species Working Group focuses on four key areas: prediction and prevention; early detection and rapid response; control and management; restoration and rehabilitation.[15] 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.[51]
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.[52]
Already stressed by water management and damming, the Colorado River 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, is the largest minnow native to North America and is known for its spectacular fresh water spawning migrations and homing ability. Despite a massive recovery effort, its numbers are in 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, largemouth and smallmouth basses, common carp, and other fishes.[53] However, the listing of these non native sport fish as invasive is controversial, as the fish are popular among anglers, who criticize the science used by government agencies and assert that nonnative species are largely a scapegoat in the decline of endemic Colorado River basin fish. Instead, they blame changes to the riparian environment primarily to dams and water diversions.[54]
See also: List of invasive species in the Everglades.
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.[55] In addition to control and prevention measures the act also calls for efforts to monitor the distribution of known invasive species.[56]
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.[57] 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.[58]
In the Pacific Northwest, non-native invasive species (NIS) present significant threats to native ecosystems, biological diversity, and the stability of soil and hydrologic systems. NIS disrupt hydroelectric dams and irrigation systems, increase the spread of wildlife diseases, increase wildfire intensity and frequency, and cost billions of dollars to the region’s economy.[59]
Invasive species are spreading in the Pacific Northwest at unprecedented rates due to large volumes of trade, tourism, and global climate change.[60] [61]
The Gulf South is an area that historically has been proven to be particularly susceptible to the introduction of non-native invasive species. The porous nature of this region and the numerous ports that reside within it contribute in large part to the introduction of non-native aquatic species. This region is home to one of the nation's most active ports (the Port of New Orleans), in addition to numerous other large ports in Houston, Mobile, Gulfport, etc. The Mississippi River provides access to 14,500 miles of connecting waterways throughout North America through the Mississippi Delta by way of the Port of New Orleans, providing for a path of little resistance for non-native species to disperse throughout the region. Among the most notable species introduced to the Gulf Coast by way of ocean-going vessels docking in these ports are: the Formosan termite arriving by way of wooden pallets unloaded in Houston during the 1940s, fire ants arriving by way of soil shipments from South America from the 1910s to 1940s, Asian tiger mosquitoes arriving through Houston during the 1980s by way of stagnant water trapped in used tires.
On the coast itself, the aquatic plant species of primary concern is the Salvinia (both giant and common). This plant was listed as a Federal Noxious Weed in 1981, before this classification it arrived in America by way of Brazil to be used as a novelty plant in aquatic gardens/aquariums.[62] These plants grow entirely or partially submerged in water, and their areas of influence include wetlands, lakes, rivers, estuaries, coastal zones, irrigation systems, hydroelectric systems, and aquaculture facilities. In areas where this plant is allowed to flourish unchecked, it often engrosses entire riverways and lakes. For example, Lake Bistineau and Caney Lakes in Webster Parish, Louisiana were entirely choked out by this invasive aquatic weed. This plant has an incredible capacity to dominate competing organisms within its ecosystem, it owes this status to its short reproductive cycle, high genetic variability, and to the fact that it can survive in nearly any type of aquatic environment.
The most problematic terrestrial plant species of this region is the Chinese Tallow tree, which was introduced to the United States in the 1700s for the purpose of cultivation in commercial nurseries. The plant was primarily cultivated for its seeds, which produce a waxy substance used in soapmaking. This tree has infiltrated the entirety of the Southeast United States, spanning from East Texas all the way to North Carolina, but it is especially prolific in the Gulf South Region. This species is particularly damaging due to the fact that its root systems change the chemical balance of soil, which in turn serves to alter the composition and structure of the native ecosystem's plant life. These trees have experienced a rapid expansion throughout the Gulf Coast region and, due to the fact that they out-compete much of the native vegetation, they threaten these areas by creating a lack of diversity which will inevitably lead to the creation of a dangerous mono-culture. Additionally, when found in wetland or marsh communities (like those found all throughout the Gulf Coast), this tree has been shown to adversely affect the amphibian and reptile populations of those regions.[63]
The lone mammalian species threatening the gulf coast is a large rodent known as the nutria. This species was brought to Louisiana by way of South America in hopes of bolstering a domestic fur trade. However, enough of these animals escaped and made their homes in the thousands of coastal bayous and waterways to have become a problem. These rats annually damage 100,000 acres of coastal wetlands with their ravenous appetite for aquatic plants, making this already vulnerable region even more susceptible to coastal erosion.[64] Additionally, they are notorious for destroying crop yields. Nutria rats have been the target of one of the most well-known and effective control programs ever utilized by environmental protection agencies. The state of Louisiana offers $6 per Nutria tail delivered to collection centers run by local wildlife and fisheries authorities. The projected annual goal of this program is to harvest 400,000 nutria annually.[65]
Non-native invasive species may be as disruptive as climate change to the Pacific Northwest and prevention and management efforts are acutely underfunded.[66]
Since the Pacific Northwest was one of last regions of the United States to be fully colonized by Europeans, a greater proportion of native ecosystems remain intact than elsewhere on the continent.[67]
Major conservation efforts are directed towards native Pacific Salmon because they provide substantial benefits to countless species and the general health and function of coastal ecosystems. Although hydroelectric dams, hatcheries, harvest, and habitat loss dominate the discourse on salmon population decrease in the Pacific Northwest, non-native invasive species (NIS) may have a greater impact than all of these four aspects combined through the mechanisms of predation, competition, infection, and habitat modification.[68]
The removal of non-native invasive species (NIS) from Pacific Northwest forests can increase the quantity and diversity of native herbs and woody plants within a short time frame and without human intervention through passive forest recovery mechanisms.[69]
Soil pathogens pose a significant barrier to ecological restoration efforts across multiple habitats in the Pacific Northwest as non-native invasive species are notably less vulnerable to pathogen attack than native ones.[70]
Specific non-native invasive species can actually assist efforts to conserve native species by generating shelter and food for rare species, carrying out beneficial ecological services, providing functional replacements for extinct species, and possessing greater resilience to land and climate changes.[71]
The lack of knowledge on the present and future effects of climate change on the biota of the Pacific Northwest is vast, just a sprinkling of studies address this issue.[72]
Ecologists hypothesize that the effects of climate change on NIS in the Pacific Northwest are likely to include: (1) different introduction modalities, (2) altered impacts of existing NIS, (3) different distribution patterns of existing NIS, (4) increased biological invasions, and (5) altered efficacy of current NIS management techniques.[73]
See also: List of invasive plant species in Arizona.
See main article: List of invasive plant species in California and List of invasive species in California. 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.[74] California has many diverse ecoregions, and numerous endemic species that are at risk from invasive species.[75]
See also: List of invasive plant species in Connecticut.
See also: List of invasive species in Florida. Invasive species in Florida currently make up more than 26% of the animal population and a full one third of the flora population.[76] In 2015, the presence of the invasive land planarian Platydemus manokwari was recorded from several gardens in Miami. Platydemus manokwari is a predator of land snails and is considered a danger to endemic snails wherever it has been introduced.[77]
See also: Invasive species in Hawaii and List of invasive plant species in Hawaii. Measures to prevent the introduction and spread of invasive species are coordinated by the Hawaii Invasive Species Council.[78] Currently the council is broken into five committees which focus on different areas of invasive species control. These focus areas are: prevention, management of established pests, increased public awareness, research and technology, and monetary resources.
Currently, Hawaii requires inspection of any and all plant, animal and microorganism transports.[79] 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.[80] Many potential invasives or carriers for invasives require permits and quarantine periods before entry to the state is allowed.[81]
In addition, there are other preventative measures such as a hotline for reporting sightings of known potential invaders like the brown tree snake.[82]
The Idaho Department of Agriculture has around 300 introduced or exotic species listed with 36 classified as noxious weeds. The legal designation of noxious weed for a plant in Idaho can use these four criteria:[83]
Some of the plants on Idaho's noxious weed list that are harmful or poisonous are:
New Orleans, the "gateway to the Mississippi", is a porous port city with rich soils. In turn, many aquatic plants are introduced to the region, making Louisiana the state with the second largest list of invasive aquatic species,[85] second to Florida.
The "Dirty Dozen"[86] details a list of the United States' most destructive invasive species. Of the twelve, four are identified in the state, including the zebra mussel, tamarisk, hydrilla, and Chinese tallow.
See also: List of invasive plant species in Maryland.
See also: List of invasive plant species in Nevada.
See also: List of invasive plant species in New Jersey.
See also: List of invasive plant species in New Mexico.
See also: List of invasive plant species in New York.
The New York State Department of Environmental Conservation works with stewards of natural resources, non-profits and citizen scientists to detect, record and manage invasive species. These collaborations are organized into eight Partnerships for Regional Invasive Species Management (PRISMs) throughout the state. PRISMS perform the following tasks: plan regional invasive species management;develop early detection and rapid response capacity; implement eradication projects; educate the public in cooperation with DEC contracted Education and Outreach providers; coordinate PRISM partners; recruit and train volunteers; support research through citizen science.[87] [88]
Counties of New York list invasive species in varying order of threat.[89] [90] [91] [92] [93] Insects considered invasive include: Asian longhorned beetle; emerald ash borer; and spotted lanternfly.
See also: List of invasive plant species in Oregon.
See also: List of invasive plant species in Pennsylvania. Pennsylvania has a Governor's Invasive Species Council which devises action plans to deal with threats to the Commonwealth's agricultural and natural resources.[94] Spotted lanternfly is one of the newest and most urgent threats to businesses in Pennsylvania including vineyards and wineries, orchards and hops producers.[95] [96]
Species of concern in Rhode Island include burning bush (Euonymus alatus), Oriental bittersweet (Celastrus orbiculatus), and purple loosestrife (Lythrum salicaria).[97]
See also: List of invasive species in Texas.
See also: List of invasive plant species in Utah.
See also: List of invasive plant species in West Virginia.
See also: List of invasive plant species in Wisconsin.