HOW ONE TINY SALAMANDER AFFECTS AN ENTIRE FOREST’S CARBON CYCLE
By Betsy L. Howell
The ensatina, a small salamander with shoe-button eyes and orange and brown mottling, lay very still on the forest floor. As a warm, Pacific Northwest rain fell gently on both of us, I could almost hear this animal thinking, “Here I was, perfectly happy beneath that piece of bark you just overturned. Now, what can I help you with?” Ensatinas, unlike the other terrestrial amphibian I most often encounter — the western red-backed salamander — rarely hurry off when I find them. In anthropomorphic terms, they seem very patient, almost polite. I have seen many ensatinas in my years as a wildlife biologist with the U.S. Forest Service and my admiration for a creature that lives such a different life from my own is great. These creatures’ small size belies the essential role they play in the complex system of the forest — a system that we all depend on. When I finally leave and replace the bark roof over the salamander, it’s as if there is the faintest of whispers: Thank you.
Ensatinas (Ensatina eschsholtzii) are about half the length of a pencil when full-grown and completely terrestrial. They leave their underground worlds only on warm, moist days and nights, when they come to the surface to take refuge from the sodden ground under pieces of bark. Apart from their large eyes, they are easily identified by bright, yellow markings on the tops of their legs and a slight constriction at the base of their tails. “Ensatina,” a Latin word meaning “sword-like” refers to the way the tail is held straight and displayed to predators. They are a lungless salamander, meaning that they absorb oxygen solely through their skin. This makes them extremely sensitive to changes in air temperature and humidity. However, they also seem to be a very adaptable species. I have observed them in older forests, younger forests and even sometimes on the edges of clear-cuts. The species also has an extensive geographic range, occurring along the west coast of North America, from Baja California in Mexico to southern British Columbia in Canada.
Because ensatinas live only on land, they do not lay their eggs in water as some salamanders do. Instead, after an elaborate dance between the male and female that signals the beginning of the breeding cycle, the male will deposit a packet of sperm, known as a “spermatophore,” on the forest floor. The female then takes the packet into her cloaca and the sperm moves from this transport vessel into a part of her body called the spermatheca. When she decides that conditions are favorable, generally in the spring, the sperm is released inside her body and she will deposit her fertilized eggs in rotten logs, underground burrows or any location that is protected and contains adequate moisture. The new mother then guards the eggs throughout the summer until they hatch in August or September.
For biologists, the life of the ensatina is fascinating. For the average person, it may be less so. If I tried to describe this subterranean world at a social gathering, I would likely encounter polite boredom. If I tried to use the word spermatophore in general conversation, I would definitely regret it. I can hear people’s questions already. What have ensatina salamanders to do with me? What does it matter if they live in the forest or they don’t live in the forest? In short, who cares? Conserving the unusual, little-known species and making its presence relevant in the world of people can be a terrific challenge. Yet, there is reason to care. If I have learned one thing, it is this: Everything is connected. Every living creature affects, and is affected by, every other living creature.
In the mid-1970s, studies conducted in New Hampshire determined that land-dwelling salamanders existed in tremendous numbers in eastern forests. In one hectare — an area the size of a football field — approximately 2,950 salamanders were counted. This biomass — that is, the total weight of all of the salamanders — was double that of birds during the breeding season and equal to that of small mammals year-round. Most of these salamanders were the eastern red-backed, a cousin of the western species I so often spot. In another study in New York, it was found that the eastern red-backed salamander directly influenced the community of invertebrates that consume leaf litter. In essence, the salamanders were a kind of super predator on animals like beetles. Because ensatinas are the most common terrestrial salamander in western coastal forests, is it possible that they fulfill the same role? And if so, what is the significance of such an ecological job? These questions were waiting for someone to answer them.
BEST MAN FOR THE JOB
Michael Best is a research scientist who has been studying ensatinas in northern California since 2006. His work has taken him far from his childhood home of Queens, N.Y., where growing up in an urban environment didn’t deter his inherent interest in the natural world. As a child, Best explored vacant city lots, capturing insects and observing small animals. When only six years old, he started a “bug club.” One accomplishment of this club included breeding praying mantises and populating one of the vacant lots with them. Still, amphibians and reptiles, even more than bugs, became the animals that captured his imagination.
“The most significant salamander moment for me as a youth,” Best recalls, “was discovering the adorable, solitary tiny red efts (juvenile eastern newts) wandering through the forest, completely unafraid due to their deadly toxins.”
Likewise, witnessing the migration of thousands of spotted salamanders and spring peepers (small chorus frogs), as well as observing a snapping turtle digging her nest in the Adirondacks propelled Best toward a bachelor’s degree in conservation biology at State University of New York College of Environmental Science and Forestry. After his undergraduate work, he read a 2004 scientific review by Robert Davic and Hartwell Welsh, two well-known herpetologists. “On the Ecological Roles of Salamanders” explained the abundance of salamanders in forest ecosystems and how these animals function as regulators of food webs, species diversity and ecosystem processes. However, despite much being known about these amphibians, there were still many questions. The mystery of how western forest salamanders affect invertebrate densities gave rise to a master’s project for Best. He soon found himself in the King Mountain Range in southern Humboldt County, less than 10 miles from the Pacific Ocean, peering into the little-known world of the ensatina.
Best’s study area, shielded from maritime influence by a rugged landscape known as the Lost Coast, is dominated by a Mediterranean weather pattern. The cool, very wet winters are perfect for the ensatina who, being lungless, requires damp environments to breathe through its skin. During the dry summers, ensatinas take refuge underground. The forest here is mixed hardwood and conifer and includes such species as Douglas-fir, tanoak and madrone. Owing to private ownership that has allowed the trees to grow for many decades, the forest floor is largely open. There is no herbaceous layer of ferns and herbs except for tree seedlings and a shrub component that includes only huckleberry bushes. The leaves of the deciduous tanoaks and madrones accumulate every year in deep, wide swaths on the ground, eventually curling and drying into brittle crackling forms.
SOLVING THE MYSTERY
The project began with Best building and transporting 12 “salamander housing units” to the study area. These were walls constructed from sheet metal sections a foot tall, inserted into the ground to enclose a 100 square-foot area of the forest floor. This area was then further divided by interior walls, creating four salamander plots. Best made sure each contained slabs of Douglasfir as cover for the animals.
He then removed all salamanders from half of the plots, while the other half had just one adult male ensatina each. “We used male ensatinas,” Best explains, “because it was possible that nesting females could exhibit specific behavior attributes that would have biased our results. After laying eggs, females might stay underground longer and feed less, or they might consume only certain kinds of invertebrates and not others. We wanted to be careful not to introduce that kind of bias.”
Best had constructed short, overhanging edges on the tops of the structure walls to prevent escape by the study salamanders, as well as immigration by other salamanders. However, in the first few weeks after setting up, he still encountered baby ensatinas and California slender salamanders that had emerged from the leaf litter. These extra animals were then carried to areas outside of the study. Though the treatment salamanders weren’t marked, Best could identify them by their length and weight, which he had previously measured.
Finally, into each plot went three bags of forest leaf litter weighing exactly three grams each. Invertebrates consume leaf litter, and with that consumption, carbon is released into the atmosphere. These invertebrates will keep eating until something stops them — say, a hungry salamander that sees them as a meal. Since fresh, dry leaf litter is 50 percent carbon by weight, the amount of leaf litter weighed later in the study would reflect changes in the amount of carbon remaining on the forest floor in the plots. Best wanted to measure the difference between the plots in which some of the invertebrates were being eaten and those in which they faced no threats, leaving their leaf litter-eating mission unchecked.
With the plots now ready, Best began his study by creating a grid pattern of 100 points, then randomly selected five points for invertebrate sampling. Firmly inserting a soup can with both ends removed through the leaf litter down to mineral soil, he extracted cores full of different species of insects. Samples were taken each month in each plot for four months. In the first year of the study, Best documented a staggering 14,000 individual invertebrates from the plots, while in the second year — owing to early spring rains and an increase in soil moisture — he found almost 33,000. Since he had sampled only five of the 100 points in each plot, “this number,” he says, “is conservatively less than five percent of the invertebrates actually on the plots in each year.”
STEWARDS OF THE FOREST
Similar to earlier results obtained in the east, Best found that ensatina salamanders have enormous effects on their environment. Only a month into the study, the experimental plots that had a salamander showed a marked decrease in the number of large invertebrate leaf-litter shredders, such as beetles and fly larvae. This in turn resulted in 13 percent more leaf litter remaining in these plots than in the plots with no salamanders, which meant that more carbon continued to be stored in the ecosystem. Conversely, plots without salamanders had more invertebrates, which consumed the leaf litter, resulting in the release of carbon into the atmosphere. The ensatina’s removal of these large and competitive shredders also opened up food resources for tiny grazers, such as mites and barklice. These animals, which are crucial in the consumption of fungi and bacteria, could then increase in numbers.
Having ensatina salamanders doing their job seems to clearly mean more leaf litter is retained on the forest floor, which means less carbon is released into the atmosphere. This retained material is then available for another forest process called humification. In contrast to decomposition, which is about decay, humification involves the creation of humus, the rich, organic matter that is the basis for all life in the forest. “Each process is always happening simultaneously,” explains Best, “but the ratio of each to the other may increase or decrease based on weather patterns and trophic dynamics.” Measuring humification is difficult, so Best does not know to what extent this process is happening, but he can definitively say that an ensatina salamander’s presence in his study plots resulted in a smaller proportion of leaves being converted into carbon dioxide, thus making this organic material available for the creation of humus.
In a perfect world, every species would be valued and given ample space to simply be without needing to justify its existence. With so many creatures whose function we still don’t understand, it seems prudent to make no such judgments about which are, or are not, important. Yet, we don’t live in a perfect world, and judgments, acknowledged or not, are made every day. Even the tendency for humans to conserve animals most like ourselves doesn’t always hold true. Certain species, coyotes and crows for example, with their tremendous adaptive capabilities, intelligence and devotion to family (characteristics all much admired in the human realm), often inspire our greatest wrath. Yet, prudent thinking and sound research show again and again the wisdom of Aldo Leopold’s words about maintaining all the pieces of an ecosystem: A thing is right when it tends to preserve the integrity, stability and beauty of the biotic community. It is wrong when it tends otherwise. This is a moral and practical philosophy. Michael Best believes that woodland salamanders are the stewards of the forests, silently channeling invertebrate biomass into energy and maintaining productive ecosystems. Even if the ensatina’s shoebutton eyes, interesting courtship rituals or strange life underground aren’t enough to pique someone’s attention, the animal’s effect on the storage of carbon in a world whose atmosphere is already overloaded with it should be.
Betsy L. Howell is a wildlife biologist who has worked for the U.S. Forest Service for 20 years.