Invasive species affect the nation’s military installations and operations worldwide. The National Wildlife Federation’s recent report (Westbrook and Ramos 2005) on invasive species on military lands provides twelve cases outlining numerous threats and costs to military operations: from six-foot tall spiky yellow star-thistle shredding parachutes that average $4,000 apiece to Phragmites causing security concerns at Avon Park Air Force Range. Holloman Air Force Base allocated over a half million dollars to remove invasive species from airstrips in order to protect the safety of Air Force pilots and prevent damage to aircraft worth tens of millions of dollars. And in Hawai`i, dense non-native mangrove thickets can breach “line of sight” security for Marines assigned to protect base borders along the shoreline (Westbrook and Ramos 2005).
Ecological impacts
Many reports have documented the ecological impacts of these non-native invaders, including citing invasive species as one of the greatest threats to biodiversity (e.g. Stein et al. 2000). Worldwide, an estimated 80 percent of endangered species could suffer losses due to competition with or predation by invasive species (Pimentel et al. 2005). In addition to direct competitive impacts to native species, some of the worst invasive species are able to alter native habitats and ecosystems. Invasions by non-native species have been shown to modify ecosystem processes, like nutrient cycling, fire frequency, hydrologic cycles, sediment deposition, and erosion (Kelly 2007). On the Marine Corps Base Hawai`i, non-native mangrove stands take over native marsh habitats, converting critical habitat for endangered Hawaiian waterbirds into mangrove thickets that are inhospitable to both native species and to realistic military training exercises on base. On Avon Park Air Force Range in Florida, invasive wild hogs compete with the endangered Florida scrub jay for food and destroy nesting habitat for many other endangered species (Westbrook and Ramos 2005). Such feral hogs are a growing menace at several other military Page 270 of 293 installations. When invasive species cause habitat destruction and harm rare native species, the result can lead to reductions in available training lands on installations.
Economic impacts
Invasive species impact the United States economy in many ways, negatively affecting economic sectors such as western ranching, Great Lakes shipping, southern forest plantations, and midwestern farming, just to name a few. Within the U.S., the estimated damage and management cost of invasive species is more than $138 billion annually, more than any other natural disaster (Pimentel et al. 2005). In addition to these costs, many economic losses from recreational and tourism revenues are difficult to calculate (Simberloff 2001); as a result, the $138 billion estimate may be low.
If monetary values could be assigned to the extinction of species, loss of biodiversity, and reduction of ecosystem services, costs from impacts of invasive species would drastically increase (Pimentel et al. 2005). For the military, the costs related to invasive species are significant and are increasing each year. To name one example, Camp Pendleton in southern California spent approximately $1.2 million over a five-year period trying to control giant reed (Arundo donax) and tamarisk (Tamarix ramossima) (Westbrook and Ramos 2005). While it also can be expensive to prevent invasive species on military lands—for example through programs to wash tanks and other military vehicles before and after transport—prevention is a critical first-line defense against new invaders on military lands. Once established, managing invaders such as the giant reed and tamarisk, mentioned above, can often be a multi-year and multi-million-dollar effort.
Recreational impacts
As many boaters and fishermen can attest, invasive species like water hyacinth (Eichhornia crassipes), hydrilla (Hydrilla verticillata), Eurasian milfoil (Myriophyllum spicatum), and water chestnut (Trapa natans) can reduce or prevent access to water bodies. In some cases, it is the recreational activities that have introduced or spread invasive species. So have people out for innocent walks; Miconia calvescens, a broad-leafed plant introduced as a handsome ornamental in Hawai`i in the 1960s, produces tiny seeds that must be removed from shoe soles by vigorous brushing, lest they plant themselves elsewhere. It and other invasives can limit hiking options or reduce the outdoor experience. Conservative estimates of the economic costs from invasive species impacts on wildlife-related recreation in Nevada alone range from $6 million to $12 million annually (Elswerth et al. 2005).
Invasive species vectors
Invasive species have arrived in the United States through a multitude of means, including introductions by early human settlers who seek reminders of their homelands, to importation of ornamental plants, to introductions by government agencies to combat some other problem (often an agricultural one), to an expanding global trade enterprise that inadvertently allows the rapid spread of species. Modern trade has increased the spread of several species. Asian tiger mosquitoes hitchhike into new areas in rainwater pools in discarded tires and even aboard water-filled depressions on ship structures. This mosquito is associated with the transmission of many human diseases, including dengue virus, West Nile virus, and Japanese encephalitis (Global Invasive Species Database 2006).
Ship ballast, typically water pumped into a ship’s tanks at one port and pumped out at another, is used to balance the weight and control the steerage of freight vessels and is a well-documented vector. The most noted species introduced by ballast is the zebra mussel. Zebra mussels (Dreissena polymorpha) are native to the Caspian Sea, but long ago began spreading throughout much of Europe. In 1988, they were detected in the Great Lakes where they had caused serious problems by out-competing native species for food and damaging harbors, boats, and power generation plants.
In some cases, the military itself unintentionally may have been responsible for the spread of invasive species. While it is difficult to pinpoint the precise time, location, and cause of introduction, there is speculation that the military introduced the brown tree snake to Guam, African iceplant to the San Francisco Bay area, black rats to the Midway Islands, and sakosia shrubs (Timonius timon) to Palau. The military has taken a leadership role to reduce future unintentional introductions. The Armed Forces Ballast Water Management Program, which requires DoD vessels to twice flush ballast water at least twelve nautical miles from shore, should be used as an example to commercial vessels. Transportation policy and procedures rules already require the washing of vehicles after field operations. The primary purpose is to extend the life of field equipment, but it also has a secondary purpose of reducing hitchhiking foreign pests from entering U.S. borders.59
59 See Retrograde Washdown: Cleaning and Inspection Procedures. Armed Forces Pest Management Board. Technical Guide No. 31. November 2004.
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Author
Troy Weldy, Invasive Species Expert
The Nature Conservancy
Invasive Species Management
Impacts on military operations