Invasive Plant Management in the United States ... - ACS Publications

Chapter 7

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Invasive Plant Management in the United States National Wildlife Refuge System Michael Lusk*,1 and Jenny Ericson2 1Chassahowitzka 2National

National Wildlife Refuge Complex, Crystal River, Florida Invasive Species Program, U.S. Fish and Wildlife Service, Arlington, Virginia *E-mail: [email protected]

Invasive species pose a significant challenge to the National Wildlife Refuge System and have been identified as the single most important threat to habitat management on refuges. At present, it is estimated that over 2 million acres of refuge lands are invaded by invasive plants. The current and potential costs of controlling invasive plants, as well as monitoring and restoring refuge lands, are significant both financially and ecologically. Budgetary expenditures for invasive species projects in FY 2009 totaled $18.4 million. A number of strategies are used to confront this threat and have resulted in success on a variety of levels. The Refuge System utilizes key partnerships, invasive species strike teams, and a dedicated cadre of volunteers to implement projects that incorporate mechanical, chemical and biological control methods.

I. Introduction The U.S. Fish and Wildlife Service (USFWS) National Wildlife Refuge System (NWRS) is a network of habitats that support a diversity of wildlife and provide outstanding outdoor experiences for all Americans. The approximately 100 million acres of terrestrial lands and waters, plus 50 million acres of marine resources in the Pacific, include 548 wildlife refuges, thousands of waterfowl protection areas, and many special management areas, such as federally designated wilderness areas and biosphere reserves. While the Refuge System

This chapter not subject to U.S. Copyright. Published 2011 by the American Chemical Leslie and Westbrooks; Invasive Plant Management IssuesSociety and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

protects fish and wildlife and their habitats, it also provides opportunities for public activities and uses. The Refuge System also manages for wildlife-dependent recreation activities, protects historic sites, and supports scientific research. As mandated under the National Wildlife Refuge System Improvement Act of 1997, the six wildlife-dependent recreation activities include hunting, fishing, wildlife observation, photography, environmental education, and interpretation (1).


A. Overview of the Invasive Plant Problem on U.S. National Wildlife Refuges The USFWS manages invasive plants on National Wildlife Refuges because these species have the potential to degrade habitats and in turn, affect the wildlife that the Service is mandated to protect for the continuing benefit of the public. Many of the invasive plants that are found on refuges are nonnative species that were either intentionally or accidentally introduced into the United States. Without their native predators and parasites, some introduced species are able to outcompete, and sometimes totally replace native plants and animals. Invasive plants such as kudzu [Pueraria montana (Lour.) Merr.] cause a number of problems. Invasive plants: -

form monocultures that utilize the resources (nutrients, light, and water) that native plant communities need to grow; change ecosystem processes such as fire frequency; hybridize with native species and cause a loss of genetic material; threaten agriculture and livestock; and, pose a threat to rare and endangered species.

However, not all non-native plants are invasive or cause problems. In fact, most of our most widely used agricultural crops were introduced from other parts of the world (e.g., wheat, rice, and potatoes). Depending on the land management goals of a refuge, managers may work towards creating desired plant communities which may include both native and non-native plants. However, NWRS policy clearly states that primary management focus should be on maintaining and restoring native ecosystems (2). B. National Wildlife Refuge Acres Infested with Invasive Plants Invasive species continue to be one of the greatest challenges for managers in the NWRS. At the 2001 Conservation in Action Summit, invasive species received twice as many votes as any other issue in the Wildlife and Habitat Challenges section. When the Refuge System’s Threats and Conflicts Database was filled out by managers in 2003, invasive species were the most frequently cited threat to the Refuge System. Moreover, the results of a survey of refuge managers published in 2008 indicate that invasive plants are the most common problem affecting habitat trends on refuges. In the same survey, when refuge managers were asked which management action had increased the most in cost from 2002 through 2007, invasive plant management was the number one reported action (3). And, according to the 2009 Refuge Annual Performance Planning database 70 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


(RAPP), the number of acres reported to be infested with invasive plants rose from 2.3 million acres in FY 2008 to 2.5 million acres in FY 2009. While the Refuge System is committed to controlling and eradicating invaders, a total of 325,000 infested acres were treated in FY 2009 – a 2% reduction from FY 2008. On a positive note, fewer invasive animal populations (3,894) were reported on refuge lands in FY 2009 than in previous years (4,423 populations were reported in FY 2007) (4) (Figure 1).

Figure 1. Invasive plants on National Fish and Wildlife Service Refuges. Data Source: Refuge Resource Management Information System and Refuge Annual Performance Plan. (see color insert) C. Costs Associated with Invasive Species Management on National Wildlife Refuges According to the Refuge System’s Activity Based Costing (ABC) accounting system, refuges spent an estimated $18.4 million on invasive species management activities in FY 2009 – up from $11.3 million that was spent in FY 2007. This represents a 300% increase over the $6 million that was spent in FY 2004. Beginning in FY 2009, the Refuge System designated a $1 million annual fund to large projects that strive to eradicate an invasive species. This is a significant commitment because these funds are meant to support projects that aim to truly eradicate, rather than just control, a species in a given area. Projects are selected through an internal competitive allocation process. In FY 2009, $1 million in funding was awarded to Palmyra Atoll in the Pacific for the eradication of rats. And, in FY 2010, the funds were awarded to Humboldt Bay NWR for the eradication of Denseflower cordgrass (Spartina densiflora Brongn). This strategy represents a unique approach among federal land management agencies in dealing with invasive species. In most cases, monies for addressing invasive species are divided between several regions or geographic areas. As a result, many projects 71 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


may be started, but few result in eradication of a targeted invasive species because there is not enough money to complete the project. By dedicating a large sum of money to one or two projects annually, this helps assure that a project can be followed through to completion (Figure 2).

Figure 2. Cost of invasive species management on National Wildlife Refuges. (see color insert)

II. Recent Invasive Species Management Projects In FY 2009, the USFWS received $280 million from the American Recovery and Reinvestment Act (ARRA). Numerous invasive species projects were supported with these funds. In Alaska, where many invasive plants are just beginning to invade, USFWS partnered with the Alaska Association of Conservation Districts and other state groups to employ an early detection and rapid response (EDRR) strategy to locate and control a number of new invasive plant infestations. Target EDRR species included Common tansy (Tanacetum vulgare L.), White sweetclover [Melilotus officinalis (L.) Lam.], and Spotted knapweed (Centaurea stoebe L.). In other states, such as Montana, North Dakota, Colorado, and Utah, youth groups were employed to assist refuges with invasive plant control. For example, at the Rocky Mountain Arsenal NWR, the Mile High Youth Corps invasive weed removal crew surveyed 162 acres of habitat suspected of being infested with houndstongue (Cynoglossum officinale L.) (Figure 3). In addition to handpulling houndstongue they encountered, they also removed and chemically treated Scotch thistle (Onopordum acanthium L.), Musk thistle (Carduus nutans L.), and mullein (Verbascum thapsus L.). These invasive plants outcompete native species for sunlight, nutrients, water, and space – and reduce the amount of foraging habitat for wildlife. 72 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


Figure 3. Removal of houndstongue from the Rocky Mountain Arsenal by the Mile High Youth Corps Invasive Weed Removal Crew. All images by Michael Lusk, FWS, unless otherwise noted. (see color insert) A. Eradication of Rats on the Palmyra Atoll National Wildlife Refuge in the Pacific Recently, funding has been made available for large invasive species eradication projects on refuge lands. In FY 2009, these funds were awarded to Palmyra Atoll NWR for eradication of rats. Palmyra Atoll, a circular string of 52 islets that is about 1,000 miles southwest of Hawaii, is home to over a million birds of 29 species, including one of the largest Red-footed booby (Sula sula L.) colonies in the world. (Palmyra Atoll NWR consists of about 680 acres of above-water forest lands and 515,232 acres of submerged lands and open water, including approximately 16,094 acres of coral reef habitat. It is the only undeveloped and unpopulated wet atoll left in the tropical Pacific.) As the only suitable nesting site in 450,000 square miles of the central Pacific Ocean, it is critical foraging and breeding habitat for thousands of seabirds. Rats are known to have a significant impact on seabird populations on the islands, and are thought to be responsible for numerous extirpations and population declines. At Palmyra, rats have been observed preying on seabird eggs, chicks, and adults. They also directly compete with the birds and other native wildlife by eating insects and other terrestrial invertebrates. The goal of the project is to totally eradicate them from the island. B. U.S. Fish and Wildlife Participation in the Federal/State Effort To Eradicate the Gambian Pouched Rat from the Florida Keys The Gambian pouched rat (Cricetomys gambianus Waterhouse), which is native to Africa, is generally 20-35 inches long (50-87 cm), has a long white-tipped tail, and weighs up to nine pounds (4 kg) (Figure 4). It was first 73 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


introduced onto Grassy Key (a 1,500 acre island in the Florida Keys about 60 miles north of Key West) as an exotic pet in the late 1990s. The current breeding population on the island descended from pet rats that escaped into the wild sometime between 1999-2001 (5–7).

Figure 4. Michael Lusk with a Gambian pouched rat on Grassy Key, Florida. (see color insert)

If permitted to spread to the U.S. mainland via the Florida peninsula, this rat would pose a serious threat to agriculture (especially fruit production), not to mention native plants and animals. Without any native predators and parasites to control their populations, Gambian pouched rats would outcompete native animals for food, carry diseases, and damage native bird populations by eating their eggs. Peterson et al. determined through computer modeling that the rat has a strong potential to become established as an invasive species across much of the United States (8). In 2007, the USFWS provided $120,000.00 to assist USDA APHIS Wildlife Services in their efforts to eradicate the Gambian pouched rat from Grassy Key and Crawl Key, in the Florida Keys. While the exotic rats have not invaded neighboring islands encompassing National Key Deer Refuge, assisting APHIS in the effort will ultimately save millions of dollars that will be needed to control them in the future. Since 2004, when a breeding population of the rat was first documented on Grassy Key, the USDA, USFWS, and the Florida Wildlife Commission have spent about $250,000 on the eradication effort. Gambian giant pouched rats will be considered eradicated from Grassy Key when intensive surveys do not detect the presence of rats for a minimum of two years. At that point, periodic surveys will be conducted well into the 74 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


future to ensure that no remnants of the population have gone undetected and survived to breed. Areas with any detected rats will be targeted with intensive control efforts (9). [Like many other invasive species, the Gambian pouched rat does have beneficial characteristics that often complicate efforts to prevent their spread. Their uses in Africa to detect landmines in crop fields, and to detect the tuberculosis bacterium in human saliva, are two examples. Due to their keen sense of smell, Gambian pouched rats are trained from an early age to associate the smell of explosives with a food reward, such as a banana or a peanut. When an area has been swept, a team with metal detectors is used to detonate live mines that are detected by the rats. Gambian Pouched Rats are also being trained to detect the Tuberculosis Bacterium (Mycobacterium tuberculosis Zopf, http://en.wikipedia.org/wiki/Mycobacterium_tuberculosis) in human saliva. Since Tuberculosis is responsible for 1.7 million deaths annually, and with 9.2 million new cases each year, mainly in poor countries, the rats could help with early detection and treatment of this deadly disease (10)]. Another reason for concern about this large African rodent is that it is believed to be a contributing factor in the current outbreak of monkeypox in the United States. In 2003, the Centers for Disease Control (CDC) and the Federal Drug Administration (FDA) issued an order preventing the importation and sale of this and a number of other rodent species following reported outbreaks of the disease that were traced to a shipment of rodents that were imported from Ghana by a Texas animal distributor. In September 2008, the FDA and the CDC lifted the ban on pouched rats as pets in the United States. However, they are still illegal to import from other countries (10).

C. Removal of Saltcedar at Muleshoe NWR in West Texas Since 2003, the staff at Muleshoe NWR on the high plains in west Texas has been working to control saltcedar (Tamarix ramosissima Ledeb.) around the lakes on the refuge (Figure 5). The biggest challenge has been getting access to the shoreline when the winds are favorable for foliar herbicide applications. However, recent improvements in herbicides and equipment, combined with persistent control efforts and follow up monitoring, have paid off in habitat improvements, benefiting shorebirds, waterfowl, Sandhill cranes (Grus canadensis L.), and prairie chickens. Paul’s Lake, which is one of the lakes on the refuge, used to dry up every summer. But with the removal of saltcedar, the spring-fed playa now provides open water habitat all year long. In conjunction with this effort, a Partners for Fish & Wildlife program has been working to control saltcedar on neighboring private lands, thereby removing seed sources from the local playa lake watershed.

75 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


Figure 5. FWS staff treating saltcedar at the Muleshoe National Wildlfe Refuge in West Texas. (see color insert) D. Controlling Purple Loosestrife on the Montezuma NWR with Biological Control Agents In 1951, there were sparse stands of Purple loosestrife (Lythrum salicaria L.) on the Montezuma NWR, which is located at the north end of Cayuga Lake in the Finger Lakes Region of New York State. By 1980, this introduced invader from Europe had covered 1,500 acres of the refuge’s 3,200 acres of wetlands (Figure 6). This prevented FWS staff from lowering water levels in the refuge pools to expose mudflats that are crucial habitat for migratory shorebirds. In 1996, a biological control program utilizing introduced beetles and weevils that feed exclusively on purple loosestrife was initiated. As a result of the program, purple loosestrife now grows on less than 10% of refuge wetlands, and allows refuge staff to manage the wetlands for migratory birds and other wildlife.

Figure 6. Purple loosestrife crowding out native wildflowers in a field at the Montezuma National Wildlife Refuge. URL: http://www.pixdatabase.com/photo/494/ (see color insert) 76 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

III. FWS Invasive Species Strike Teams – Mobile Response Units


The USFWS Invasive Species Strike Teams (ISST) are mobile response units that are designed for rapid response and eradication of new weed infestations on FWS refuges. There are currently five Strike Teams in the Refuge System. The teams are based in Hawaii and the Pacific Islands (Region 1); Arizona and New Mexico (Region 2); south Florida (Region 4); the upper Missouri/Yellowstone/ upper Columbia River basins (Region 6); and North Dakota (Region 6). Table 1 summarizes ISST activities in FY 2007.

Table 1. Activities of FWS Invasive Species Strike Teams in 2007 ISST Operational Areas

Acres Treated

Acres Surveyed

FY07 Allocation

Pacific Islands

270

252

$490,036

Arizona and New Mexico

398

Not Applicable

$520,759

South Florida

13,751

Not Applicable

$409,257

Missouri, Yellowstone, and Upper Columbia River Basins

10,310

27,000

$409,257

North Dakota

25,228

55,140

$490,036

IV. The Role of Volunteers in Combating Invasive Species on FWS Refuges Volunteers play a vital role in efforts to combat invasive species on the nation’s wildlife refuges. The Volunteer and Invasives Program (VIP) is funded by a special Congressional appropriation that is received annually. FWS partners in the effort include the National Wildlife Refuge Association (NWRA), The Nature Conservancy (TNC), and the USGS National Institute of Invasive Species Science, which is based in Ft. Collins, Colorado. Volunteers assist with all aspects of the USFWS Invasive Plant Management Program. They map invasive plants with GPS units, enter data into computers, manually pull invasive plants, release biocontrol agents, apply herbicides, help to restore native habitat, and help to educate the public about the problem. Without volunteers, much of the invasive plant work that is accomplished in the USFWS Refuge System would not be possible. A. Accomplishments of the FWS Volunteer and Invasives Programs The NWRS Invasives & Volunteers Program continues to engage large numbers of volunteers in invasive species management activities on refuge lands across the country. Beginning in FY2010, management of this program will shift 77 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


from the national office to the NWRS regional offices. Since 2005, more than 5,600 volunteers have contributed 86,800 hours to the treatment, inventory, and restoration of over 415,000 acres of refuge land. As one successful example of volunteer partnerships, funding from the program has enabled Boy Scout Troop 224 of Willmar, MN, to assist staff at the NWRS Weber Waterfowl Production Area with the removal of invasive woody vegetation (Figure 7). Invasive plants, such as European buckthorn (Rhamnus cathartica L.) degrade grassland and oak savanna habitat for migratory birds that depend on these habitat types. Using loppers and handsaws, the Scouts cut back invasive plants and FWS staff members treat the stumps with an herbicide. After removal of the vegetation, more than 50 species of native plants are seeded and planted. So far, over 800 hours of volunteer service have been provided by the Scouts on 115 acres at the Weber Waterfowl Production Area since 2007.

Figure 7. Removal of European buckthorn from the Weber Waterfowl Production Area near Willmar, Minnesota, by Boy Scout Troop 224. (see color insert)

V. Summary The National Wildlife Refuge System manages the largest network of public lands and waters set aside primarily for the benefit of wildlife in North America. Invasive plants and animals have repeatedly risen to the forefront as being the greatest threat to wildlife habitat and one of the leading drains on management budgets within this national system of lands and waters. Every year, a greater percentage of base budgets is used by field stations to combat invasive species. To address the threat of invasive plants and animals, and protect the natural biodiversity under its charge, the NWRS has pursued a variety of innovative approaches. The NWRS has made the unusual move to commit a large sum of money, $1 million annually, to one or two large projects, rather than dividing it up among many small projects. This results in projects that are actually able to achieve eradication or significant control, whereas this would not be possible 78 Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


under the routine system of dividing funds among many small projects. Several recent projects have focused on eradicating invasive animals, such as removal of rats from Rat Island in Alaska and Gambian pouched rats in Florida. Investing up-front in total eradication of a species lowers long-term costs by eliminating the need for control in the future. To vigorously respond to incipient infestations of invasive plants, the NWRS adopted the mobile Strike Team approach pioneered by the National Park Service, which was in turn based upon “hot shot” fire crews. In the long term, funding is saved by investing in control up-front, before the infestations grow out of hand. The NWRS has also been a leader in recruiting volunteers specifically to help with invasive species projects. Through providing funds targeted at invasive species projects, the NWRS has encouraged a tremendous response in local communities. These projects not only provide a great deal of free labor for the refuge, but also help to educate the public on the threat of invasive species to their local native ecosystems.

References 1. 2.

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U.S. Fish and Wildlife Service, 2010. http://www.fws.gov. Policy on Biological Integrity, Diversity, and Environmental Health; 601 FW 3; U.S. Fish and Wildlife Service, Department of the Interior: Washington, DC, 2001. Wildlife Refuges: Changes in Funding, Staffing, and Other Factors Create Concerns about Future Sustainability; GAO-08-797; U.S. Government Accountability Office: Washington, DC, 2008; pp 43, 52. National Wildlife Refuge System: Invasive Species Program Fiscal Year 2009 Update, U.S. Fish and Wildlife Service, 2009. http://www.fws.gov/ invasives/pdfs/InvasiveSpeciesProgramFactSheet_2009.pdf. Engeman, R.; Woolard, J. W.; Perry, N. D.; Witmer, G.; Hardin, S.; Brashears, L; Smith, H.; Muiznieks, B.; Constantin, B. Rapid assessment for a new invasive species threat: The case of the Gambian giant pouched rat in Florida. Wildlife Res. 2006, 33, 439–448. Perry, N.; Hanson, B.; Hobgood, W.; Lopez, R.; Okraska, C.; Karem, K.; Damon, I.; Carroll, D. New invasive species in southern Florida: Gambian rat (Cricetomys gambianus). J. Mammal. 2006, 87, 262–264. Keys Treasures Blog. Gambian Pouch Rat on Upper Matecumbe Island in Florida, December 30, 2007. http://floridakeystreasures.com/keysblog/2007/ 11/04/giant-gambian-pouch-rat-found-in-islamorada/. Peterson, A.; Papaş, M.; Reynolds, M.; Perry, N. D.; Hanson, B.; Regnery, R.; Hutson, C.; Muizniek, B.; Damon, I.; Carroll, D. Native–range ecology and invasive potential of Cricetomys in North America. J. Mammal. 2006, 87, 427–432. Engeman, R. M.; Witmer, G. W.; Bourassa, J. B.; Woolard, J. W.; Constantin, B.; Hall, P. T.; Hardin, S.; Perry, N. D. The Path to Eradication of the Gambian Giant Pouched Rat in Florida. In Managing Vertebrate Invasive Species, Proceedings of an International Symposium; Witmer, G. W., Pitt, W., Fagerstone, K., Eds.; USDA/APHIS/WS, 79

Leslie and Westbrooks; Invasive Plant Management Issues and Challenges in the United States: 2011 Overview ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


National Wildlife Research Center, Fort Collins, CO, 2007, pp 305−311. http://www.aphis.usda.gov/wildlife_damage/nwrc/symposia/ invasive_symposium/content/Engeman305_311_MVIS.pdf. 10. Gambian Pouched Rat. Wikipedia, 2009. http://en.wikipedia.org/wiki/ Gambian_pouch_rat.

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Invasive Plant Management in the United States ... - ACS Publications

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