DoD Biodiversity Conservation Handbook
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Chapter 8: The Effects of Natural and Man-Made Disturbances

Military Disturbances and Associated Ecosystem Consequences

Ground disturbances at bombing ranges, such as here at theWarren Grove Air National Guard Range, New Jersey, are typical of impacts caused by military training operations. (Photo: Douglas Ripley)

Military lands are important ecological reserves because they often encompass large tracts of land that are protected from intensive agriculture and urban development (Boice 1997, Ripley and Leslie 1997a, 1997b, Lillie and Ripley 1998). Furthermore, some of the finest examples of fire-maintained ecosystems within the southeastern United States are found on military bases in and adjacent to artillery ranges where frequent fires are assured and unexploded ordnance provides protection from development (Peet and Allard 1993). But how do military training activities compare to the natural disturbance regimes? And how might military disturbances interact with land management activities on military bases?

Disturbances from military missions may enhance or exacerbate their effects on ecosystem components. In general, military training in terrestrial environments can be broadly categorized into two major types of disturbances – ground maneuvering (tracked and wheeled vehicles) and air-to-ground impacts. Military installations subject to usage by the U.S. Army are often subject to additional impacts from training exercises. Typically, maneuvers on Army installations involve large vehicles that can cover large areas in a single training exercise. The available land base for training has a strong influence on the intensity and frequency of usage (Demarais et al. 1999) and thus on the disturbance effects.

Large-vehicle maneuvers are a widespread use of land and consistently are shown to have negative effects across a variety of terrestrial ecosystems. These repeated human-induced disturbances have no natural analog. The negative effects of ground maneuvering training have been studied in California (Lathrop 1982, Prose 1985), Colorado (Milchunas et al. 1999), Georgia (Dilustro et al. 2002), Kansas (Quist et al. 2003), Washington (Severinghaus and Goran 1981), Wisconsin (Smith et al. 2002), Texas (Severinghaus et al. 1981), Manitoba (Wilson 1988), and western Europe (Vertegaal 1989). Although studies have been conducted across a variety of ecosystems (e.g. deserts, prairies, pine-oak forests, etc.) several generalizations have emerged. In particular, it is the cumulative effect of repeated military disturbances that ultimately results in reduced abundance of perennial species, overall losses of native species, increased numbers of introduced species, and an increase in the amount of bare and compacted soil.

The careful cleanup of inert ordnance at the Barry M. Goldwater Range, Arizona, is an important part of the range restoration programs by the U.S. Air Force and U. S. Marine Corps. (Photo: Douglas Ripley)

While most studies have focused on effects of large vehicles, the observed results probably also include the effects of other vehicular disturbances as well (i.e. off-road vehicles) that oftentimes occur in conjunction with tracked vehicle maneuvering activities. Road-like features, including active and remnant trails and vehicle tracks, are the most prevalent disturbance features at installations with high-usage maneuvering areas (Dilustro et al. 2002, Quist et al. 2003). These disturbance features act to increase fragmentation of the landscape, which can in turn affect ecosystem-level processes (i.e. spread of fire, flooding, drainage, etc.).

In native grasslands where maneuvering has been examined, at least one study, (in Central Plains grasslands at Fort Riley Military Reservation in northeast Kansas), has shown increased bare soil, reduced total plant cover, and compositional shifts in plant communities (Quist et al. 2003). Reduced cover of the perennial, matrix-forming grasses and native species, and increased cover of annual and introduced species were also associated with high-usage maneuvering training activity. Quist et al. (2003) also reported high-usage maneuvering associated with increased sediment and reduced abundance of benthic insectivores, herbivore- detritivores, and silt-intolerant aquatic species. Watersheds with high military maneuver usage also were characterized by an abundance of trophic generalists and disturbance-tolerant species. Overall, the Quist study suggests that high-usage maneuvering areas had significant ecological effects on the properties of both terrestrial and aquatic ecosystems, with respect to recovery from past disturbances and ecological resilience to future disturbances. In an effort to prevent significant degradation of training areas and to provide a coordinated assessment and monitoring of these impacts, the U.S. Army has implemented an Integrated Training Area Management (ITAM) program.1 This program emphasizes monitoring of military impacts (erosion, siltation, soil compaction, loss of native plant cover, hydrologic alterations, etc.) on training lands.

Seven students from the Young Women's Leadership School in New York City's Harlem assist in various aspects of the Mill Creek stream restoration project at Eglin Air Force Base, Florida. This program is part of an ongoing effort to restore streams on the Eglin Reservation that are home to the endangered Okaloosa Darter. (Photo: Jerron Barnett, U.S. Air Force)

In contrast to ground maneuvering activities, air-to-ground missions are capable of mimicking natural disturbance regimes in some ecosystems. This is particularly true when active bombing and gunnery ranges exist within fire-evolved ecosystems like prairies, savannas, and some wetland types. Aerial bombing and gunnery ranges used by fighter and bomber aircraft, and artillery and mortar gunnery from ground-based weapon systems can provide the ignition sources in fireevolved ecosystems. Some of air-to-ground ranges that date back to pre-World War II contain remnant fire-maintained plant communities no longer found in the surrounding fire suppressed landscape.

An impact area on Avon Park Air Force Range in central Florida known to receive over a thousand high explosive rounds and several thousand non-explosive rounds strikes annually (Delany et al. 1999) has created a long history of frequent mission-caused wildfires that in turn have provided some of the variation inherent under a natural fire regime. Ordnance-ignited wildfires on this impact area are frequent (>1/yr), may occur year-round, and have occurred since the 1940s. As a result, the vegetation within the impact area has never been fire suppressed. Despite bomb craters created by high-explosive munitions, portions of the impact area with native vegetation support endangered birds, numerous rare plant populations, and some of the highest natural-quality examples of fire-maintained plant communities found in central Florida (Orzell 1997). Similar native speciesrich plant communities, often containing enclaves of rare plants, have been recorded elsewhere in or near active air-to-ground impact areas in the southeastern United States (Peet and Allard 1993, Sorrie et al. 1997).

Restoration of long-leaf pine forests and red-cockaded habitat at Fort Stewart, Georgia. These scenes show various stages of the prescribed burning process and the final result of a mature long-leaf pine forest providing excellent habitat for the endangered red-cockaded woodpecker. (Photo: U.S. Army)

The influence of anthropogenic disturbance, in particular that associated with land management activities (forestry, grazing, etc.) and the military mission on ecosystem-level processes, is also pertinent when discussing disturbance effects. The interactive effects of ecological disturbance regimes and human disturbances (resulting from land management and military activities) also need to be considered, but few studies have examined these interactions. A study conducted by Dilustro et al. (2002) at Fort Benning, Georgia, in the Fall Line Sandhills ecoregion found significant interactions with other activities. In particular, forestry management practices with heavy mechanized training sites were found to favor pine dominance, and open-site, successional or fire tolerant ground cover plant species (Dilustro et al. 2002).2

Proceed to Next Section: Management Implications

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About This Chapter's Author
Steve Orzell is a botanist/ecologist at Avon Park Air Force Range.

William J. Platt is a professor of population biology/ecology at Louisiana State University.

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