As discussed in Chapter 6 “Partnerships to Achieve Conservation Goals and Sustain Training,” effective conservation often depends on coordination with public and private landowners in the region surrounding a base. One piece of information that can inform interactions with neighbors as well as the investment in management of a species is the relative management responsibility of a base. If a base has one of the largest populations of a species (for example, gopher tortoise on Eglin Air Force Base in Florida), then investment in its protection is likely very important compared to a situation in which a base has a small population that is one of dozens for a species. Calculation of management responsibility requires information about sizes of populations across the species range, distribution maps, or habitat models run for the entire range. Be careful with small populations—satellite populations at the edge of a range might have unusual genetic variation that is important to the evolutionary potential of the species. Be aware also that a base may become increasingly favorable habitat for a species as the climate changes.
Tracking population trends
Knowing population size and how fast it is increasing or decreasing are fundamental inputs into management decisions but often surprisingly elusive metrics to come by. Species vary tremendously in their natural histories and life cycles, typically requiring tailored monitoring approaches for different species. Approaches include measuring the size or percent cover of occupied habitat, counting individuals or egg masses, and using models to estimate occupancy of habitat patches. As for surveying, population monitoring must take place during appropriate seasons and weather conditions. In some situations, base personnel can conduct the monitoring rather than relying on a partner. Regardless of who does the monitoring, an often-overlooked aspect is managing and archiving annual measurements to support future long-term analyses.
Population viability
What’s the chance that a population will persist over the next X years? A population viability analysis (PVA), a modeling approach that estimates a population’s risk of extirpation, can answer this question (Traill et al. 2010). PVA will work only on well-studied populations with a good run of population trend data and other information to estimate parameters for the model. Done well, PVA can support a sensitivity analysis that identifies the factors and life stages having the greatest influence on the future population trends. This information is invaluable for deciding how to invest resources in different management strategies.
Conservation genetics
Small or isolated populations are always in danger of losing genetic variation and succumbing to inbreeding and the accumulation of deleterious genes. Knowing a population’s genetic diversity is valuable for determining its risk of extirpation from one of these factors. Methods for measuring genetic variation advance rapidly and vary widely across species. A partnership with an academic lab with the equipment needed to run the analyses is key. Although many genetic measurements require invasive sampling (plant leaves or animal blood), increasingly noninvasive techniques such as the use of scat samples are becoming available.
Climate change vulnerability assessment
A climate change vulnerability assessment (CCVA) helps understand how and the extent to which climate change threatens a population (see Chapter 8, “Managing Landscapes and Ecosystems”). CCVA approaches for TES species may focus on species’ traits or use habitat models run with future projected climate data as inputs to estimate vulnerability (Foden et al. 2019).
Diseases and invasive species
Both diseases and invasive species can have devastating impacts on species of interest. Managers at island bases are well aware of the destructive power of invasive predators and competitors such as pigs, goats, and rats. Species of interest on mainland bases are also susceptible to invasive plants that outcompete native plants.
Strategies
Armed with a list of TES species and assessment of their populations and potential stressors, base managers can then consider strategies to slow or stop declines or enhance existing populations. Here we list some common strategies for management interventions of TES species. As with many of the tools listed in this chapter, outside help is typically needed to carry out these actions due to the high technical expertise needed and public scrutiny that comes with working with high profile species.
Habitat management—Natural resource managers have designed countless ways to manage habitats for TES species. The most straightforward is to restrict human entry and disturbance to the habitat used by the target. Restrictions can be limited to a targeted time period if harmful activities take place when the target species has either migrated elsewhere or is in an inactive phase. For example, restricting access to cliffs where peregrine falcons nest can be limited to the breeding season. Training during the rest of the year will have little impact on the falcons as long as artillery practice does take aim at the cliffs. On the other hand, off-season use of heavy vehicles in areas with vernal pools used for reproduction by rare amphibians can compact soils and negatively affect hydrological periods.
Many forested ecosystems, especially those dominated by conifers and grasslands require fire at appropriate frequency to maintain their function. Controlled or prescribed burns are often critical to maintaining the integrity of these systems to promote regeneration of desired tree species and reduce understory vegetation. Timing is key for successful controlled burns. The season for burning should be chosen to avoid affecting the target and nontarget species, and the specific date of the burn should coincide with favorable weather conditions. The spatial scale of burns is another important consideration as some species benefit from a mosaic of habitats that result from small-scale fires burning in different years.
Invasive species management is often called for when invasive species are major threats. This practice can take many forms depending on the nature of the threat, from eradication of introduced mammals on oceanic islands to the use of controlled burns to reduce the expansion of invasive grasses. Herbicides are sometimes used for aggressive invasive plants with no other practical means of control. Biocontrol through the release of animals (often insects) or disease agents, although attractive in theory, has had mixed results and requires a careful analysis of benefits and risks (Heimpel and Cock 2018). In some cases, native species such as white-tailed deer have become super abundant and require population control similar to that used for invasive species to reduce impacts on target species (Pendergast et al. 2015).
Where food limitation limits breeding success or juvenile or adult survivorship, food supplementation may benefit target species. Supplementation may be direct (e.g., setting out cow carcasses for California condors) or indirect by planting vegetation that provides food resources, enhancing the habitat for prey species, or, in extreme cases, reducing populations of competitor species. A good assessment study will be valuable to identify the life stage that would benefit from food supplementation to avoid unnecessary expenditure of resources on what is typically a resource-intensive management action.
Other habitat enhancements may help replace missing features in an ecosystem to the benefit of a target species. For example, nest boxes can substitute for woodpecker holes in old growth trees, artificial burrows can be used where gopher tortoises have disappeared, and artificial ponds and wetlands can make up for the loss of natural ones.
Restoration—Restoration is an extreme form of habitat management where the goal is to return a system to some historical state. In practice, the aim is typically to recover a natural range of ecosystem composition, structure, and dynamics. In the context of TES species, managers employ ecological restoration to recover aspects of an ecosystem that have been lost but are needed for the population to prosper. As highlighted above, military bases often have exceptional examples of natural ecosystems and therefore less need for restoration. However, to fulfill the needs of a target species, restoration may be called for in some cases. The base might have an abandoned training area, airstrip, landfill, or other site that could be converted into a wetland, grassland, or forested habitat. Because restoration is often the most expensive management action available, decisions about embarking on such a project should be carefully considered and executed with advice from experienced professionals.
Ex situ conservation—Ex situ conservation is a strategy to consider for species occurring in habitats that have become too degraded to sustain the population even with intensive habitat management or other in situ actions. Again, military bases often have extensive intact ecosystems such that ex situ conservation will rarely be necessary. It might be an option, for example, if a small population of a TES species is newly discovered in an area that has already been heavily degraded by training or for base infrastructure and the population is in imminent danger of extirpation. Any ex situ conservation efforts will most likely involve coordination with FWS personnel that can take the lead in providing access to the necessary captive rearing facilities. For plants, the FWS is also an important ally but the botanical garden and seed banking community are additional resources.
Translocation—Another high-profile strategy, translocation, involves moving individuals from one site to another. Translocation has been used to augment genetic diversity of an isolated subpopulation by bringing in individuals from different subpopulations. An entire subpopulation under threats that are beyond immediate mitigation can be translocated to another area where the chances of survival are higher. Currently, one of the threats that can trigger such an action is climate change. If a climate is becoming unsuitable to the point of threatening the persistence of a subpopulation and natural dispersal is prevented (e.g., by anthropogenic barriers), then translocation to a site with a more favorable climate may be the option.
Deciding between alternative strategies
Sometimes the strategy needed to protect a species is obvious. Perhaps a TES amphibian is not reproducing because the temporary pools where they reproduce always dry up before the tadpoles can undergo metamorphosis. Adding water to the pools to increase the hydroperiod will probably be successful. More often, there is enough uncertainty around the results of an assessment such that the best strategy is unclear. Uncertainty around how the climate might change and how a species will respond can suggest multiple plausible strategies, each with a different cost. How do we determine which to pursue?
The best bet is to undergo a structured decision-making process. Identifying clear objectives, alternative actions, how different actions might affect outcomes, and risks can provide a transparent framework for deciding among alternative strategies. Fortunately, structured decision making is now widely used in natural resources management and there are many resources available to learn from.
Next Page: Resources
Author
Bruce Young, Ph.D., Chief Zoologist and Senior Conservationist Scientist
NatureServe
Managing for Threatened, Endangered and At-Risk Species
Managing for Threatened, Endangered and At-Risk Species