National Wildlife Refuge System
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Invasive species pose a growing threat to biodiversity around the planet, not to mention food crops, commerce and human health. Increasingly, scientists are trying to put a price tag on the problem. In fiscal year 2008, the National Wildlife Refuge System spent more than $15 million on invasive species control efforts.

Now, a study assessing related costs across the Atlantic has found that some of the invasives most destructive to refuges in the U.S. also cost Europe the most either in damage or control efforts. Among these are water hyacinth, a fast-growing aquatic weed (responsible for $4.6 million in costs, estimated the European study); nutria, a large semi-aquatic rodent also known as coypu ($3.95 million); ice plants ($800,000) and longhorn beetle ($740,000).

The study’s lead author, Montserrat Vilà of the Estación Biológica de Doñana of Seville, Spain, also produced a list of the top 10 invasive species in Europe with her colleagues. Besides nutria, several creatures on the list are also regarded as pests on U.S. national wildlife refuges, such as Zebra mussels. Canada geese, which earned a place on the list, are not labeled as invasive here in the U.S., but are subject to management by the Fish and Wildlife Service because overabundant flocks pose health and safety risks.

Michael Lusk, the Refuge System’s invasive species coordinator, said the European study shows the need to work more closely with international partners on the problem. The study was recently published in the Ecological Society of America’s online journal, Frontiers in Ecology and the Environment.

While cost comparisons are not exact because study methods and time spans differ, the size of the outlays on both shores underscores the severity of the problem. In a report released in September 2008 by the U.S. Government Accountability Office, national wildlife refuge managers cited invasive plants as the leading problem affecting habitat trends. Of the managers who responded, 78 percent reported invasive plants to be a large to moderate problem; 42 percent put invasive animals in that category. Refuge managers also identified invasive plant management as the management action that had increased the most in cost between fiscal years 2002-2007.

European researchers note the frustrations of trying to manage some invasives. For example, they cite a 2007 study showing that nutria’s damage to agriculture and riverbanks in Italy was undiminished by a five-year effort to control the pest.

Eradication efforts in some parts of the Chesapeake have had more success. The U.S. Fish and Wildlife Service teamed with the U.S. Department of Agriculture to rid Blackwater National Wildlife Refuge in Maryland of nutria in 2004, after the pests permanently ruined 5,000 to 8,000 acres of marshland. Stephen Kendrot, a field supervisor for the nutria eradication project, said the Service is spending $1.5 million a year to eradicate the species from the rest of the Delmarva (Delaware-Maryland-Virginia) peninsula. The cost to the Bay economy of not managing nutria, he said, has been estimated at $35 million a year.

Fighting harmful invaders occupies two full-time staffers and part of the time for a third at the Arthur R. Marshall Loxahatchee National Wildlife Refuge, located within the northernmost point of the Everglades in Florida. This year, said senior biologist Cindy Fury, the refuge will spend $5 million to control two major plant pests: lygodium, or old world climbing fern, and melaleuca trees. Neither species has any known predators. “Lygodium climbs up trees, like kudzu, blocks the sunlight and kills the tree,” said Fury. “It’s completely changing the ecosystem if we can’t get a handle on it.”

Contact: Michael Lusk, Invasive Species Coordinator at 703-358-2110 or

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