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Invasive species management can be controversial. It may seem paradoxical, and perhaps even wrong, that The Nature Conservancy is involved in killing wild organisms just because they are in the wrong place. But we do not control invasive species because we dislike them or think they are "evil." Rather, we control invasive species if and when they interfere with our mission to protect native biodiversity. It is a tragedy when we must kill organisms, be they plant or animal or otherwise. The fault lies with us for spreading the organisms to areas where they threaten native biodiversity, and the invasive organisms are in effect paying for our errors.

Staff of The Nature Conservancy face this responsibility gravely, and make sure we are operating with the best possible scientific knowledge. On our pages here and at The Nature Conservancy's invasive species web site, we quote a number of interesting facts about invasive species. In case you would like to check our facts, we provide our sources for you here. We encourage you to read these publications and learn more about the threats of invasive species! Some of the citations are for online documents written by The Nature Conservancy, but these have their own citation lists for you to refer to.

If you are interested in the financial estimates on the impacts of invasives, a few more are given on our economics of invasives page.

On http://www.nature.org/initiatives/invasivespecies/ we say...

"...the estimated damage from invasive species worldwide totals more than $1.4 trillion--five percent of the global economy."
See: Pimentel, D., McNair, S., Janecka, J., Wightman, J., Simmonds, C., O'Connell, C., Wong, E., Russel, L., Zern, J., Aquino, T. and Tsomondo, T. 2001. Economic and environmental threats of alien plant, animal, and microbe invasions. Agriculture, Ecosystems and Environment 84: 1-20

On http://www.nature.org/initiatives/invasivespecies/features/art21255.html we say...

"...purple loosestrife (Lythrum salicaria) was introduced to the USA via horticulture."
See: Anderson, N.O., and Ascher, P.D. 1993. Male and female fertility of loosestrife (Lythrum) cultivars. J. Amer. Soc. Hort. Sci. 118: 851-858. NB: Ship ballast soil also was a major pathway for Lythrum invasion.

"...scotch broom (Cytisus scoparius) was introduced to the USA via horticulture."
See: Randall, J.M., and Marinelli, J. 1996. Invasive plants: weeds of the global garden. Brooklyn Botanic Garden. 112pp.

"...water hyacinth (Eichhornia crassipes) was introduced to the USA via horticulture."
See: Penfound, W.T., and Earle, T.T. 1948. The biology of the water hyacinth. Ecological Monographs 18:4, 447-472.

"...the cane toad (Bufo marinus) was introduced for pest control for pest control in agriculture."
See: Lampo, M., and De Leo, G.A. 1998. The invasion biology of the toad Bufo marinus: from South America to Australia. Ecological Applications. 8: 388-396.

"...the cane toad (Bufo marinus) is a problem in the Caribbean and in Australia."
See: Lever, C. 2001. The Cane Toad: the history and ecology of a successful colonist. Westbury Publishing, West Yorkshire. 230pp.

"...zebra mussels (Dreissena polymorpha) were introduced to the Great Lakes from Caspian Sea tanker."
See: Snyder, F.L., Hilgendorf, M.B., and Garton, D.W. 1990. Zebra mussels in North America: The invasion and its implications. Ohio Sea Grant College Program. Online version.

"...zebra mussels (Dreissena polymorpha) threaten 140 native mussels."
See: Stein, B.A., and Flack, S.R. (eds) 1996. America's least wanted: Alien species invasions of U.S. Ecosystems. The Nature Conservancy. Arlington, VA.

"...Asian long-horned beetle (Anoplophora glabripennis) arrived from China in wood packing crates."
See: Nowak, D.J., Pasek, J.E., Sequeira, R.A., Crane, D.E., and Mastro, V.C. 2001. Potential effect of Anoplophora glabripennis (Coleoptera: Cerambycidae) on urban trees in the United States. Forest Entomology 94: 116-122.

"...Asian long-horned beetle (Anoplophora glabripennis) caused destruction of 8000+ street and yard trees."
See: United States Department of Agriculture, Animal and Plant Health Inspection Service. 2005. Asian Longhorned Beetle Cooperative Eradication Program Strategic Plan. Online version

On http://www.nature.org/initiatives/invasivespecies/about/ we say...

"...molasses grass is invasive in Australia."
See: Queensland pest series report on molasses grass

"...molasses grass is invasive in Brazil."
See: Fact sheet from Instituto Hórus

"...invasives are the primary force in the decline of 42% of the threatened and endangered species."
See: Pimentel, D., Zuniga, R., and Morrison, D. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics. 52: 273-288.

"...the annual US cost from invasives is $120 billion, with over 100 million acres being affected (i.e. the size of California). "
See: Pimentel, D., Zuniga, R., and Morrison, D. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics. 52: 273-288.

"...the cost of invasives is 5% of the global economy."
See: Pimentel, D., McNair, S., Janecka, J., Wightman, J., Simmonds, C., O'Connell, C., Wong, E., Russel, L., Zern, J., Aquino, T., Tsomondo, T. 2001. Economic and environmental threats of alien plant, animal, and microbe invasions.Agriculture, Ecosystems and Environment 84: 1-20.

"...chestnut blight arrived in the USA in 1904, causing extinction of chestnut by the 1950s."
See: Brewer, L.G. 1995. Ecology of survival and recovery from blight in American chestnut trees (Castanea dentata (Marsh.) Borkh.) in Michigan. Bull. of the Torrey Bot. Club. 122: 40-57.

"African lovegrass "destroyed the pasture value of 10% of southern grazing lands and severely damaged the area's cattle industry. Annual losses are calculated at $30 million per year."
See: Rosa, F., Ramos, J.V., and Ziller, S. 2007. Economic impacts of Eragrostis plana on the Southern Brazil grasslands. Biological Invasions (in prep.).

"...leafy spurge costs ranchers in ND, SD, MT, WY more than $144 million a year."
See: Bangsund, D.A., and Leistritz, F.L. 1991. Economic impacts of leafy spurge on grazing lands in the northern Great Plains. NDSU Agriculture Economic Report No. 275-S.

"...cactus moth in Mexico could threaten $80 million annual industry on cactus, a source of food for humans and livestock."
See: Zimmermann, H., and Cuen, M.P.S. 2006. The consequences of introducing the Cactus moth (Cactoblastis cactorum) to the Caribbean, and beyond. (www.cactoblastis.org)

On http://www.nature.org/initiatives/invasivespecies/features/ we say...

"...tree of heaven was brought to the USA as nursery stock in the 1840s."
See: Swingle, W.T. 1916. The early European history and the botanical name of the tree of Heaven, Ailanthus altissima. J. of the Washington Academy of Sciences. 6: 490-498.

On http://www.nature.org/initiatives/invasivespecies/features/art8863.html we say...

"...efforts to control loosestrife are estimated to cost $45 million per year."
See: Pimentel, D., Lach, L., Zuniga, R., and Morrison, D. 2000. Environmental and economic costs of nonindigenous species in the United States. Bioscience 50: 53-65.

"...purple loosestrife (Lythrum salicaria) was introduced in the 1800s."
See: Anderson, N.O., and Ascher, P.D. 1993. Male and female fertility of loosestrife (Lythrum) cultivars. J. Amer. Soc. Hort. Sci. 118: 851-858.

On http://www.nature.org/initiatives/invasivespecies/features/art8864.html we say...

"...mature kudzu vines can be 100 feet long."
See: Mitich, L. 2000. Kudzu [Pueraria lobata (Willd.) Ohwi]. Weed Technology, 14: 231-235.

"...kudzu was introduced in 1876 at the Philadelphia Centennial Exposition."
See: Mitich, L. 2000. Kudzu [Pueraria lobata (Willd.) Ohwi]. Weed Technology, 14: 231-235.

"...kudzu roots at its nodes."
See: Mitich, L. 2000. Kudzu [Pueraria lobata (Willd.) Ohwi]. Weed Technology, 14: 231-235.

On http://www.nature.org/initiatives/invasivespecies/features/art8865.html we say...

"...multiflora rose was introduced in 1886 from Japan as understock for ornamental roses."
See: Hoffman, R., and Kearns, K. (eds) 1997. Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants.

"...birds spread the seeds of multiflora rose."
See: Schery, R. 1977. The curious double life of Rosa multiflora. Horticulture. 55: 56-61.

On http://www.nature.org/initiatives/invasivespecies/features/art8866.html we say...

"...salvinia prevents the passage of sunlight and oxygen."
See: Thomas, P.A., and Room, P.M. 1986. Taxonomy and control of Salvinia molesta. 320: 581-584.

"...salvinia doubles in 2-10 days."
See: Thomas, P.A., and Room, P.M. 1986. Taxonomy and control of Salvinia molesta. 320: 581-584.

"...salvinia biocontrol weevil is used in 13 countries."
See: Julien, M.H., Center, T.D., and Tipping, P.W. 2002. Floating Fern (Salvinia), in Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04, 413 p.

On http://www.nature.org/initiatives/invasivespecies/features/art8867.html we say...

"...ailanthone is toxic to many other plant species."
See: Heisey, R.M. 1996. Identification of an allelopathic compound from Ailanthus altissima (Simaroubaceae) and characterization of its herbicidal activity. Am. J. of Botany. 83: 192-200.

"...ailanthus was introduced by horticulturists who thought it was a source of lacquer. "
See: Swingle, W.T. 1916. The early European history and the botanical name of the tree of Heaven, Ailanthus altissima. J. of the Washington Academy of Sciences. 6: 490-498.

"...ailanthus produces 325,000 seeds per year."
See: Bory, G. and Clair-Maczulajtys, D. 1980. Production, dissemination and polymorphism of seeds in Ailanthus altissima. Reuve Generale de Botanique 88: 297-311.

On http://www.nature.org/initiatives/invasivespecies/features/art21273.html we say...

"...invasives are the primary force in the decline of 42% of the threatened and endangered species."
See: Pimentel, D., Zuniga, R., and Morrison, D. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics. 52: 273-288.

"...a 2004 study found the annual cost of invasives to be 120 billion dollars."
See: Pimentel, D., Zuniga, R., and Morrison, D. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics. 52: 273-288.

On http://www.nature.org/initiatives/invasivespecies/howwework/art21237.html we say...

"...congress weed reduces the quality of forage lands in Ethiopia"
See: GISP case study on Parthenium hysterophorus



Q &A clinic
The most frequently asked questions answered for your edification.
The worst weeds
Learn about an invasive plant species in your neighborhood that threatens native biodiversity.
Ppt presentations
Here we have PowerPoint presentations on invasive species. Web slideshow versions are also on line if you do not want to download the PowerPoint files.
Economic impacts
It is difficult to put an accurate price tag on the costs of invasive species. Here are a few results from studies that have tried to do so.
How you can help
Steps you can take to help us protect our own wealth of native biodiversity.


Other site resources

Red Alerts!
Species which are either new to an area, or are showing alarming symptoms such as signs of signicant, new expansion.
Conservation stories
Read about how different people have had great successes dealing with invasive species.
Tool reviews
Read our reviews of hardware that are useful for those working in invasive species management.
About us
Information about the core staff of The Nature Conservancy's Global Invasive Species Team.
Contact information
How you can contact the core staff of The Nature Conservancy's Global Invasive Species Team.



Updated June 2007
©The Nature Conservancy, 2005