Although the primary mission of the Department of Defense (DoD) is military preparedness, DoD is also charged with managing the natural resources found on more than 25 million acres across the United States. Recent DoD initiatives such as the U.S. Army Environmental Strategy into the 21st Century direct each branch of the armed forces to comply with all environmental laws. This includes protecting habitat for threatened and endangered species (TES; both listed and candidate species). DoD requires installations to conserve natural resources for future generations by enacting and practicing sound management and conservation policies on lands that must also support military training exercises and weapons testing or storage.
This report is to be used by DoD natural resource policy makers, installation land managers, and the natural resource research community, in conjunction with asso ciated documents produced under this SERDP work unit (e.g., Trame and Harper 1997; Trame and Tazik 1995) to (1) develop ecosystem-based approaches to describe natural communities and TES habitat in relation to military activities, (2) evaluate military-related effects on those communities, (3) develop community-based strategies for supporting both military land use and TES habitat management, and (4) develop management solutions for military impacts to natural communities when management for TES habitat is a priority for a particular location.
This report focuses on Florida scrub, a rare and rapidly disappearing community found on dry, sandy soils that make up ancient dune systems. This community lies within a matrix of associated xeromorphic plant communities (longleaf pine, sandhill, and xeric hammock) and surrounding wetland areas. All of these communities are interconnected physiographically and are dependent on fire for persistence. Florida scrub, however, has adapted to a different fire regime than the other communities in this association. Fires in scrub occur at longer intervals and are more catastrophic than fires occurring in the other communities.
The scrub community is found mainly in Florida and is typically dominated by a dense layer of evergreen or nearly evergreen oak, or Florida rosemary (Ceratiola ericoides) shrubs, with an open to closed canopy of sand pine (Pinus clausa). Depending on the fire history, the sand pines may or may not be present. Groundcover is generally sparse and may be dominated by ground lichens. Bare patches of sand are common. The sandy soils supporting scrub are dry and nutrient poor. Nonetheless, at least 13 TES plants and 10 TES vertebrates can be found in the small fragments of scrub that can still be found on a number of military installations in Florida.
Many remaining scrub communities have been degraded by past management practices, land uses, and other human disturbances. Agriculture and forestry practices have also taken their toll on scrub in areas not managed by DoD. Human encroachment and development have been extensive, due to a burgeoning human population in Florida and the fact that these communities typically occupy areas of high real estate value. Fragmentation of scrub habitat has resulted in the extirpation of flora and fauna that are more common in contiguous habitat, due to increased land use pressures.
To protect remaining TES populations, larger patches of scrub should be restored and maintained in the context of TES habitat requirements. Degraded areas adjacent to high-quality Florida scrub can be enhanced to further increase TES habitat, thereby reducing the impacts of fragmentation. These actions will permit more effective management at the landscape level. Activities that interrupt TES populations and the natural processes that sustain them should also be avoided, or an alternative location for the activity should be sought.
Fire suppression over the past 80 years has effectively changed the natural processes and composition of many fragments of Florida scrub. A number of rare plants in this ecosystem require the structure of open patches of sand and vegetation that are created under a natural fire regime. These plants will not survive when the shrub layer grows to the point that the open patches are shaded out. Available information (Myers 1990; Christensen 1985, 1988) suggests that prescribed burning is necessary for maintenance of most scrub communities in Florida. There is no specific fire return interval applicable to all scrubs. Management guidelines should reflect the desire to maintain different stages of plant growth across the entire landscape, as each stage offers important structural attributes to different TES. Prescription fires should mimic patchy natural burn patterns in which areas of burned vegetation are not contiguous.
Recommendations by Woolfenden and Fitzpatrick (1991) for a fire interval adequate to maintain prime Florida Scrub jay habitat are suggested as a guideline for some of the other animal and plant TES. However, the catastrophic nature of fire in scrub often makes burning this habitat dangerous, especially when it is in close proximity to residential areas and other areas easily damaged by an escaped fire. Smokemanagement is also a problem. The techniques recommended for burning Florida scrub are addressed in Chapter 5. Some alternative burning strategies to use when dealing with fire and smoke management problems are also discussed. Mechanical disturbances may be another suitable substitute for high intensity fire in the maintenance of scrub.
Unlike many other habitats, altered hydrology is not likely to be an issue for plants native to scrub due to their high tolerance to drought stress. Florida scrub also tends to be less vulnerable than other communities to invasion by exotic species, by virtue of the demanding physical environment in which it grows. However, activities that disturb scrub soils can increase susceptibility of scrub to invasion by species not native to the community. Activities such as fire suppression, construct ing fire plow-lines, and road building promote invasion by exotics. Removal of exotic species also entails physical disturbance, which can destroy the very habitat managers are trying to improve. These practices should be implemented in such a way that they limit damage to the root systems of sensitive TES plants. Chemical removal (i.e., the use of herbicides) can be used when absolutely necessary but care must be taken near TES populations and in close proximity to wetlands.
Natural scrub communities in Florida are biologically diverse ecosystems. They provide habitat for at least 23 TES, many of which are protected under the Endangered Species Act. Under some circumstances, it is desirable to maintain high-quality natural communities to provide habitat for multiple native species over large areas. In particular, this strategy works well as part of the Integrated Natural Resources Management Planning (INRMP) process, within an ecosystem manage ment framework. The recommendations made in this report are intended to be applied in areas where TES conservation is the primary focus of land management, but may also support military training objectives.