orianneViews:
At the end of January, I found myself back in school at Virginia Tech pursuing a PhD after nearly four years of working in the real world. There were many factors that went into this decision, including getting to a point in life where it needed to happen soon if it was going to happen at all. More than that, I was excited by the opportunity to once again work with one of the rarest salamanders in the United States.
Flatwoods salamanders have a history paralleling that of many other longleaf pine specialists. Extensive habitat loss combined with decades of fire suppression and poor management resulted in severe population declines and extirpations. Flatwoods salamanders were originally listed on the U.S. Endangered Species Act in 1999, and this decision was updated in 2009 to reflect the taxonomic split into two species: the Reticulated Flatwoods Salamander (Ambystoma bishopi) and the Frosted Flatwoods Salamander (A. cingulatum). In the 20 years post-listing, significant strides have been made to better understand the salamander’s biology and to improve habitat for the remaining populations. However, some populations have continued to decline and almost all continue to face the threat of extinction in the not so distant future. The remaining populations are now mostly restricted to some of the largest and best maintained patches of longleaf pine flatwoods. These forests are characterized by flat topography and poorly drained soils, creating conditions ideal for small wetlands that are an integral part of the flatwoods salamander’s life cycle.
Conserving flatwoods salamanders is challenging for many reasons. Because they have a biphasic life cycle, flatwoods salamanders depend on suitable upland habitat as adults and appropriate wetland conditions for successful breeding. While these two habitats are closely linked, management decisions that benefit one do not necessarily benefit the other and managing wetland breeding habitats presents additional challenges when compared to upland longleaf pine. In general, Ambystomatid salamanders are notoriously difficult to study as adults because they spend the vast majority of their time underground. We know relatively little about adult behavior and ecology and almost never see adults after they exit breeding wetlands. This limits the ability to make targeted management decisions for adult flatwoods salamanders, and upland management focuses on maintaining longleaf pine forests through the application of prescribed fire.
Most of the targeted conservation work for flatwoods salamanders has focused on improving breeding conditions. Adult flatwoods salamanders migrate to breeding wetlands during the fall (October–December) where they lay eggs terrestrially in clumps of herbaceous vegetation. These eggs hatch once they are inundated by rising water levels, and larvae spend 11–18 weeks in the wetlands before metamorphosing into adults. Similar to upland habitats, wetland vegetation structures composed of open canopy pine and an understory of thick herbaceous vegetation are critical to successful breeding. Unfortunately, these habitats are prone to successional changes in vegetation resulting from fire suppression and exclusion (i.e., loss of herbaceous vegetation and development of thick mid-story). Prescribed fires are commonly set during the time of year when wetlands are most likely to be full of water. Thus, vegetation characteristics can degrade even on otherwise well-managed landscapes.
Restoring vegetation structure in flatwoods wetlands through fire alone can be a challenging and slow process because fires typically do not carry through wetlands without herbaceous vegetation. To speed up the restoration process, it is possible to mechanically remove shrubs from wetlands using a combination of saws and herbicide. This type of treatment rapidly lowers canopy cover and facilitates regrowth of herbaceous vegetation. Manually removing the accumulated duff layer through subsequent fire or raking can further speed up the vegetation restoration process. Fire has been successfully applied to wetlands that are challenging to burn during the summer by burning surrounding uplands first and then returning at a later date to burn wetland basins. Overall, these techniques have been successful at restoring wetland vegetation, but long-term success is dependent on appropriate fire management that considers wetland along with upland resources.
A second, and more challenging, aspect of suitable breeding conditions is the availability of water for a length of time that allows for successful metamorphosis. The regular drying period that breeding wetlands experience prevents fish predators from becoming established but can also lead to total reproductive failure when the hydroperiod (length of inundation) is shorter than the development time of flatwoods salamanders. While these species have evolved to persist through periodic reproductive failures, long droughts can threaten population persistence by severely limiting recruitment. In fact, many of the A. cingulatum populations once known from the Georgia Coastal Plain are thought to have been extirpated during a particularly bad drought.
Wetland hydroperiod is often considered the most important hydrologic characteristic for ephemeral wetland breeding amphibians. However, wetland hydrology is incredibly complex, and there are many additional factors that go into determining whether or not salamanders can successfully reproduce in a given year. For example, because eggs are laid terrestrially, too much water can also be a problem for flatwoods salamanders. If wetlands are full when adults make breeding migration, eggs may be laid in areas that will never be inundated with water, resulting in those eggs never hatching. Additionally, wetlands can dry at rates that may exceed an individual’s ability to respond to cues to metamorphose, even if large enough to do so. Wetlands dry at different rates, and there are a suite of factors that go into determining these complex processes (Chandler et al. 2017).
Issues related to wetland hydrology are difficult to address directly and will likely continue for the foreseeable future. Climate change is predicted to exacerbate these issues, and wetlands have already experienced shorter hydroperiods in recent years than they have historically (Chandler et al. 2016). Recent work has been successful at mitigating some of the challenges surrounding wetland hydrology. Salamanders can be successfully reared in tanks from either eggs or larvae until they metamorphose. This ensures that some recruitment occurs no matter how poor the environmental conditions are during a particular year. However, this is labor intensive and does not solve the problem surrounding inadequate breeding conditions. It also removes almost all of the selection pressures that the species evolved under during the larval period. We currently know relatively little about the differences between tank reared and naturally produced animals.
In addition to rearing animals in tanks, individuals of both species are currently being kept in captivity at multiple facilities. The goal for these captive animals is to begin breeding them in captivity. While it is fairly easy to raise Ambystomatid salamanders in captivity, it is significantly more difficult to get adults to breed. The environmental conditions that stimulate breeding activity and courtship must be adequately replicated. Excitingly, the San Antonio Zoo was recently successful at breeding A. bishopi for the first time in captivity! This is a promising first step to building captive colonies that may be able to one day contribute to restoring populations in parts of their range where they have been extirpated.
Despite all of the conservation successes over the last 10–20 years, flatwoods salamanders still face an uncertain future. It is difficult to solve the hydrologic issues that appear to be getting worse. A large portion of my PhD project focuses on understanding how climate change will impact breeding success and behavior in the coming years. Historical population declines have placed these two species in a precarious position. A few isolated catastrophic events (hurricanes, disease outbreaks, severe droughts) could be enough to push the species over a cliff that they cannot recover from. This has largely already happened in South Carolina and Georgia. Only time will tell how the story of flatwoods salamander conservation will end. I am excited to be back working with this charismatic species in an effort to push them away from the brink of extinction and towards a stable place in the southeast’s natural heritage.
Literature Cited
Chandler, H. C., A. L. Rypel, Y. Jiao, C. A. Haas, and T. A. Gorman. 2016. Hindcasting historical breeding conditions for an endangered salamander in ephemeral wetlands of the southeastern USA: Implications of climate change. PLoS ONE 11:e0150169.
Chandler, H. C., D. L. McLaughlin, T. A. Gorman, K. J. McGuire, J. B. Feaga, and C. A. Haas. 2017. Drying rates of ephemeral wetlands: Implications for breeding amphibians. Wetlands 37:545–557.
