The primary objective of prescribed burning at Fredericksburg and Spotsylvania County Battlefields Memorial National Military Park (Virginia) is to protect and preserve its cultural resources. Prescribed burning accomplishes this objective by controlling woody vegetation on earthworks and in fields and promoting the growth of native grasses, which are an essential element of the historical scenes. Native grass species include broomsedge (Andropogon virginicus), purpletop (Tridens flavus), little bluestem (Schizachyrium scoparium), poverty grass (Danthonia spicata), purple love grass (Eragrostis spectabilis), Indian grass (Sorghastrum nutans), and switch grass (Panicum virgatum). Burning maintains the historical view of the battlefields by suppressing forest succession and invasion of exotic vegetation. Other objectives of prescribed burning are reducing hazardous fuel accumulations around developed areas and along the park boundary, thereby reducing the potential for fire damage to park resources and adjacent lands and minimizing risks to employees, residents, and visitors.
Figure 1. An eastern harvest mouse is released after capture into the charred remains of its habitat at the McCoull House site in Spotsylvania Court House Battlefield.
Many studies have examined the effects of fire on small mammals but few have included the eastern harvest mouse (Reithrodontomys humulis; fig. 1, above), an abundant inhabitant of the fields in the park. The western harvest mouse (R. megalotis) and the meadow vole (Microtus pennsylvanicus; fig. 2), however, have received greater attention. Fire-related mortality among both R. humulis and R. megalotis adults has been documented as has that of nesting R. megalotis, which are particularly susceptible because of immobility (Erwin and Stasiak 1979). We assumed similarities between both species of harvest mouse. The extent of mortality depends upon the seasonal timing and intensity of the fire (Smith 2000; USDA Forest Service 2002). When nestlings are present, immobile R. megalotis pups suffer high mortality (Erwin and Stasiak 1979) because their nests are aboveground (Linzey 1998). Adult small mammals, including meadow voles and western harvest mice, often seek refuge in underground burrows to escape the heat of the fire. However, sometimes they cannot outrun or otherwise escape the heat and flames (Smith 2000; USDA Forest Service 2002; U.S. Geological Survey 2006). Western harvest mice generally remain in the habitat after the burn or quickly recolonize (U.S. Geological Survey 2006). Meadow voles, however, quickly vacate the burned area because of lack of cover and food. Moreover, peak densities of M. pennsylvanicus are not achieved until vegetation has regenerated enough to provide sufficient habitat requirements, typically two to five years after burning (Murphy et al. 2006; USDA Forest Service 2002; U.S. Geological Survey 2006). Though mortality is occasionally documented, the greatest impact to population densities of grassland small mammals is attributed not to direct mortality from the fire but to the relatively short-term (but significant) impact of habitat modification (USDA Forest Service 2002; U.S. Geological Survey 2006). The burning of vegetation removes the vital cover required for predator avoidance, destroys thick grasses through which small mammals construct their “runways” or travel corridors and build their nests, and affects food supplies.
Many studies have examined the effects of fire on small mammals but few have included the eastern harvest mouse.
Natural Resource Manager Gregg Kneipp began the use of prescribed grassland fires in Spotsylvania Court House Battlefield—one of four major battlefields preserved in the park—in February 2004. In accordance with the National Park Service’s Inventory and Monitoring Program, investigators coincidently initiated a mammal inventory two days after the first annual burn. Under a cooperative agreement between Frostburg State University (Maryland) and the National Park Service, graduate students conducted the inventory over the next two years, which included several trapping sessions in the burned fields. However, because neither of these efforts focused on how the fire affected movement and mortality of the park’s grassland residents, Kneipp initiated a pilot study before the third annual burn, which occurred on 28 April 2006 (fig. 3). The purpose of the pilot study was to investigate the effects of fire on small mammals. The small mammals under investigation in this study were species that had been discovered during previous research in these fields.
Though protecting and preserving cultural resources is the primary objective, knowing about the mortality and migration patterns of small mammals between open fields and forested areas during prescribed burns will provide valuable information concerning the ongoing management of these open fields. Using these research results park managers will be able to modify management practices for the benefit of both the cultural and natural resources in the park.
Tanner, C., and G. Kneipp. 2007. Effects of prescribed fire on small mammals inhabiting Spotsylvania Court House Battlefield. Park Science 24(2):41–45.
Available at http://www.nature.nps.gov/ParkScience/archive/PDF/Article_PDFs/ParkScience24(2)Winter2006-2007_41-45_TannerKneipp_2548.pdf.