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Reflections on Environmental Health in Vernal Pools

Photo by Michele Stapleton

Reflections on Environmental Health in Vernal Pools
UMaine scientists are discovering the ecological wonder of woodland wetlands

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.


Balancing 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 and developers.

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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 development.

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 cost.

"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 higher levels.

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, they deliver.

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 filled.

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 communities.

"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
November-December, 2002

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