By Antonio Seelman
Over the last two decades research on woodland salamanders, (Plethodon sp.) has changed from a taxonomically centered approach to a more holistic ideology. Woodland salamanders are viewed as an indicator species in forest ecosystems as a result of research conducted by research wildlife biologist Dr. Hartwell Welsh and her team. In addition, ecosystem processes that affect forest biodiversity such as succession, moisture cycling, and climate change have been shown to also alter woodland salamander populations.
First, we must understand what an indicator species is. Indicator species, like the woodland salamander, are organisms whose population abundance suggests a specific environmental condition. There are certain species that are sensitive enough to environmental conditions such as soil acidity, air pollution, and water contamination that their abundance will fluctuate due to these processes. These species can be used as a sign of the overall health and biodiversity of an ecosystem as their population numbers serve as a signal of change in biological conditions. Indicator species are a useful management tool that can help us monitor pollution and global warming, changing biological conditions, and indicate the health status of ecosystems such as deciduous forests.
The forest floor contains both litter and moist soil where the salamanders thrive.
Now, you may be thinking why salamanders? What makes salamanders so special that they should be considered an indicator species? These were questions that I had myself when I first started to discover articles written on plethodontid salamanders. Salamanders are amphibians and must constantly maintain moist skin in order to breathe cutaneously, and thus, require moist soil and forest floor litter. If a forested area begins to experience some degree of disturbance or climatic change which results in less soil moisture, the abundance of plethodontid salamanders will decrease as their niche begins to diminish. Additionally, drying of the forest floor may be a result of canopy clearing which dries out the soil and litter. Since vegetation requires an immense amount of moisture for physiological processes, the drying out of the soil may result in a decrease in both vegetation and the salamanders.
Fallen trees provide important microhabitats for many species of invertebrates as well as plethodontid salamanders. Species like the Northern redback salamander (Plethodon cinereus) rely heavily on the microhabitat that the fallen logs provide as they decay naturally on the forest floor. In my search for woodland salamanders I specifically targeted heavily decayed logs which were in moist areas. In most cases, the decaying logs were white in color on the inner wood and almost fell completely apart as I picked them up. An abundance of decaying logs is a good sign of an old-growth forest and it usually implies a lack of human interference over a long period of time. In managed forest stands the floor lacks downed logs as they are harvested for timber, leaving nothing behind in some cases.
Letchworth woods, (where I found the salamanders) showing all the signs of the perfect habitat for woodland salamanders.
The presence of these salamanders indicates that the forest in which they are located can be home to a plethora of micro biota which also rely on fallen logs. Large decaying logs are a sign of ecological succession and forest age so we can assume the age of the forest and salamander population numbers are probably linked. In this case, the plethodontid abundance can be correlated with local health, age and biodiversity of forests.
It is widely known that salamanders can only tolerate a short range of temperature variation and moisture. Older forests are better at maintaining the high moisture and low temperatures needed for these sensitive species to persist. As a result, the presence of woodland salamanders implies that a late seral stage forest is the paramount ecosystem for them. A seral stage is identified as a forest that approaches its climax stage. If salamander abundance is high in a particular area it is a good sign that the forest is healthy enough to make it to a late seral stage.
Tracking changes in salamanders provides ecological insights into communities of moisture loving organisms which dominate the soil and litter zones of a multitude of forests. Changes in the numbers of salamanders reflects many habitat features being balanced by forests including invertebrates, leaf litter, moisture, decaying logs, sunlight, and many others. Due to the high sensitivity of plethodontid salamanders, it is important to monitor their populations and use them as indicator species for habitat damage and get a head start on reversing the impact on local biota. This cost-effective method will help save future generations of forest organisms as we continue to use woodland salamanders as an ecologically important indicator species. Next time you go out on a hike make sure to carefully turn over a few logs here and there and maybe you will find one of these adorable amphibians. If you are interested, here is a quick tutorial on how to find salamanders, good luck!
References:
Caitlin McDonough, David Jaffe (Lead Author);Mary Watzin (Contributing Author);Mark McGinley (Topic Editor) "Indicator species". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth December 18, 2009; Last revised Date June 11, 2012; Retrieved September 28, 2012 <http://www.eoearth.org/article/Indicator_species?topic=58074>
Welsh, H. H., and S. Droege. 2001. A Case for Using Plethodontid Salamanders for Monitoring Biodiversity and Ecosystem Integrity of North American Forests. Conservation Biology 15:558–569.
Welsh, H. H., and G. R. Hodgson. 2013. Woodland salamanders as metrics of forest ecosystem recovery: a case study from California’s redwoods. Ecosphere 4:art59.
USDA Forest Service - Pacific Southwest Research Station. "Woodland salamanders indicators of forest ecosystem recovery." ScienceDaily. ScienceDaily, 28 August 2013. <www.sciencedaily.com/releases/2013/08/130828144845.htm>.