Reflections on Environmental Health in Vernal Pools
UMaine scientists are discovering the ecological wonder of woodland
About the Photo:
Wetlands ecologist Aram Calhoun is studying the ecological role of
vernal pools. Her research takes her to woodland sites like one in
Lincolnville, Maine, where she and Mark Miller of Tangle-wood 4-H
Camp and Learning Center inspect one of the many vernal pools on the
950 acres near Camden Hills State Park.
all-out preservation and development
Aram Calhoun of The University of Maine, and Michael Klemens of the
Wildlife Conservation Society have led a team of scientists and
development specialists in creating guidelines for municipalities
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From early spring to late summer,
wetlands ecologist Aram Calhoun heads for the Maine woods in search of
shallow, water-filled depressions in the forest floor. These seasonal
wet spots are often pungent and stagnant, lined with decaying leaves and
woodland debris. But what Calhoun and a dedicated band of volunteers see
in vernal pools are reflections of environmental health.
For the past four years in more than 50 pools statewide, the vernal pool
monitors have been recording the ebb and flow of animal traffic, from
frogs and salamanders to moose, raccoon and deer. At times the observers
sit in deep shadows and watch the coming and going of reptiles and
amphibians. Other times, they'll hike up their boots and wade into the
dark water and muck for a closer look at fairy shrimp or frog larvae.
They visit day and night.
Compared to larger wetlands, vernal pools are still poorly understood.
Fish don't live in them; they are known chiefly for breeding mosquitoes.
Some even dry up, then reappear every spring. Moreover, their small size
leaves most of them unprotected under Maine and federal environmental
law. As a result, these areas are under constant threat from
But now, Calhoun, her volunteer monitors and graduate student
researchers are developing profiles of these wetlands to make the case
for conservation, and they are working closely with municipalities and
the forest industry to preserve as many pools as possible. Their
strategy is to find a compromise in the age-old struggle between
preservation — in this case, of every last pool — and development at any
"People have a perception that small wetlands are everywhere, and
they're little so they really don't matter. In the developing landscape
these are the things that are most likely to be lost. They go through
the regulatory cracks. It makes sense that if these places keep blinking
out, we're going to affect the ecology of the larger wetlands and the
upland systems," says Calhoun, an assistant professor in The University
of Maine Department of Plant, Soil and Environmental Sciences.
Working with Maine's Department of Inland Fisheries and Wildlife, Maine
Audubon and other organizations, Calhoun helps to coordinate the state's
vernal pool conservation efforts. In addition, together with Susan Gallo
of Maine Audubon, she co-directs the North American Amphibian Monitoring
Project in Maine, which was one of the first states in the Northeast to
initiate the volunteer-based monitoring program. Since 1995, she has
been actively involved in the conservation of reptiles and amphibians,
some species of which depend on vernal pools to breed.
There is more at stake than a few slimy species, says Calhoun. In fact,
amphibians are a cornerstone of our forests, recycling nutrients,
aerating the forest floor and linking the bottom of the food web with
Moreover, scientists like Calhoun are finding new evidence that far from
being isolated mud holes of no particular consequence, vernal pools and
other small wetlands work ecological wonders. "You have leaves going in
and frogs and salamanders hopping and crawling out, and invertebrates
flying away. With them, they bring their biomass that other animals can
eat. These pools are often the first places to green up with vegetation
in the spring. Moose and bear and other game species visit these little
scattered pools in the landscape," she says.
In a sense, vernal pools are like cafés for critters. And best of all,
While the volunteer monitors are watching and recording, Calhoun and her
graduate students are tracking animal behavior in pools to figure out
exactly how these systems work and what they mean to the world beyond.
UMaine scientists have spent thousands of hours carefully documenting
vernal pool ecology from York County to Sears and Mount Desert islands
and Aroostook County.
They pay as much attention to the immediate surroundings as to the pools
themselves. It has become clear, says Calhoun, that amphibians can
travel 1,000 feet or more away from the pool where they hatched.
Creating narrow buffer zones to protect pools in developing areas may be
done with the best of intentions, she says, but can result in a place
that eventually turns silent because of a lack of animal life.
Understanding just how a vernal pool affects the environment is
important in helping Maine communities maintain their natural character.
"When you travel south to areas where there's more development than
there is here, species are in trouble. So it's going to happen up here
if we don't pay attention to the habitat. The problem is, vernal
pool-dependent species also depend on the upland habitats around the
pool. If you get development all around the pool — if where these
species live most of their lives is destroyed — the breeding habitat is
useless," Calhoun explains.
That is an issue that concerns Rob Baldwin, a Ph.D. student. Baldwin has
identified 365 pools in three York County towns over the past year. He
is focusing his efforts on just a quarter of the pools, trying to
determine whether the condition of the land surrounding each pool
affects amphibian reproduction.
In the course of his fieldwork, Baldwin has noticed that moose are
frequent pool visitors. As a result, he has decided to study the role of
moose dung in fueling the pools with nutrients.
Meanwhile, master's student Dan Vasconcelos has taken a different
approach. He is intensely studying amphibian ecology in three pools that
were constructed as part of the Sears Island marine cargo terminal
project at the upper end of Penobscot Bay. The cargo terminal was never
built, but what he has found has given pause to the practice of creating
new ponds in exchange for permitting wetlands elsewhere to be dredged or
All three of the ponds that were built on Sears Island were populated by
wood frogs and salamanders during their first year. Regulators
considered them a success in the first two years, says Calhoun. However,
things changed rapidly in subsequent years. One pond fails to dry down
during the year and has become a favorite haunt for predatory green
frogs that feed on wood frog and salamander larvae. The second pond
dries up in most years and produces a handful of wood frogs, but green
frogs have caused problems there, too. The smallest and most successful
pond dries up quickly in the summer and this year produced more than
10,000 wood frogs.
To find out how the small pool affects its surroundings, Vasconcelos
trapped and, one-by-one, applied a harmless dye to 10,000 wood frogs
during the animals' migration away from the pool. It was a laborious
task, involving weeks of capturing and releasing young frogs and then
looking for dye marks as the frogs moved into the woods. And the result?
They found that frogs were migrating 1,000 feet and more away from the
pool. Thus the researchers clearly made the case that preserving a wood
frog population in a single pool requires substantially more than a 50-
or 75-foot buffer.
Two more of Calhoun's students are nearing completion of their projects
in Acadia National Park on Mount Desert Island. Jesse Cunningham, a
master's student, is studying how beaver dams affect amphibians in
pools. Mary-Beth Kolozsvary, a Ph.D. student, is looking at networks of
vernal pools to determine how they affect the composition of amphibian
"We're trying to get rid of the notion that vernal pools are isolated.
In fact, many vernal pools are connected to other wetlands through
groundwater," Calhoun says.
"We can also document the way that bull frogs, green frogs, mink,
turtles, raccoon, and other species use these little oases in the
landscape. I see the smaller wetlands on the landscape supporting the
more permanent ones — those traditionally considered the high-value
wetlands where you can boat or fish."
Vernal pools continue to be lost to development and scientists have yet
to determine how each species responds to such a loss. For example,
spotted salamanders, which can live for 20 years, lay eggs in more than
one pool. Yet wood frogs live for up to five years and are much more
selective about where they breed. In many cases, these animals remain
faithful to the ponds where they were born.
"When you have creatures that have such a high biomass in the
surrounding upland forest, they must have an effect on nutrient cycling,
carbon dynamics and aeration in the forest floor. There are some very
complex interactions between amphibians and other aspects of our
environment," says Calhoun.
That's why it's important, she says, that people make the link that
these animals are bioindicators of environmental quality and, hence, our
quality of life.
by Nick Houtman
for more stories from this issue of UMaine Today Magazine.