Old News Archive

Vernal Pools – A Vanishing Resource

April 17, 2007 - TRC

May flowers are not all that April’s showers bring in Maine. Heavy rains accompanied by the season’s first warm temperatures also herald one of the Northeast’s most spectacular, if unseen, wildlife migrations. Emerging from under their deep, leafy retreats, legions of Maine’s wood frogs and spotted mole salamanders (so named for their tendency to spend daylight hours underground) move en masse toward small woodland pools marking one of the first signs that spring has finally arrived.

Up to 9 inches in length and sporting a seemingly unnatural yellow, polka-dotted pattern across a polished black body, the yellow spotted salamander would be hard to miss were it not for the fact that it spends most of its life in small mammal burrows or under fallen logs, far from the wooded pools it breeds in. Similarly, wood frogs recognized by their dark, raccoon-like mask and tan or chocolate-colored bodies, may travel ¼ mile or more in their efforts to return to the same forest pool where they transformed from an aquatic tadpole to a terrestrial frog some one or two years before.

While perhaps unnoticed, be assured that the abundance of pool-breeding amphibians (frogs, toads, and salamanders) occupying the forest floor around some woodland pools can be tremendous. Indeed the collective weight (or “biomass” as scientists refer to it) of these unseen spring sentinels has been estimated to exceed that of all birds and mammals combined in some forests with productive breeding pools ! Their sheer abundance and palatability (to raccoons, coyotes, snakes, hawks, and just about any other predator that finds them) has many ecologists convinced that the terrestrial wanderings of these pool-breeding frogs and salamanders play a powerful role in the local ecology of our forests.

Wood frogs, spotted salamanders, and blue-spotted salamanders are part of a specialized fauna in Maine that breed almost exclusively in small, isolated forest pools that are fed by spring rains and melting snow but dry partially or completely by late summer. These ephemeral spring wetlands, referred to by ecologists as “vernal pools”, are exploding with the sounds and movements of ducks, frogs, salamanders, turtles, snakes, dragonflies, fairy shrimp and other creatures early in the year, but lie surprisingly empty and dormant by late summer.

What draws amphibians and invertebrates to breed in these fleeting pools? – their lack of fish. Isolated from streams and subject to periodic drying, vernal pools provide a nearly predator-free haven for wetland wildlife that lack the defenses necessary to reproduce in more fishy environs. Of course, in nature every lifestyle bears inherent tradeoffs, and for those choosing ephemeral pools life is a constant race against the drying clock of summer. In severe drought years vernal pool-breeding species may suffer catastrophic losses if their home dries up before larval stages can complete development and transformation into the terrestrial juvenile phase.

Less certain than the rain is whether the vernal pools themselves will survive to greet another spring migration of forest-dwelling frogs, salamanders, and turtles. Residential development and urban sprawl are taking its toll on wetland habitat, particularly in southern and coastal Maine where some towns have recorded population growth rates of up to 30% in just the last ten years. While open space for all of Maine’s wildlife suffers from unplanned and unchecked development, smaller wetlands, such as vernal pools, are being lost and degraded at an especially high rate. Part of the problem stems from a gap in current state wetland laws, designed primarily to protect wetlands over 1/3 acre in size. Unfortunately, most vernal pools are smaller than this, thus receiving little or no protection.

The Department of Inland Fisheries and Wildlife is cooperating with the Departments of Environmental Protection and Conservation, Maine Audubon Society, and the University of Maine to identify potential strategies for protecting the unique wildlife values associated with smaller wetlands that currently “fall through the cracks” of current wetland regulations. Workshops on vernal pools continue to be held throughout the state for land managers, educators, and land trusts, and several new publications designed to provide landowners voluntary techniques for protecting vernal pools and their wildlife are now available. The Maine Citizen’s Guide to Locating and Documenting Vernal Pools provides a comprehensive introduction to recognizing and monitoring vernal pools, including color photographs of the indicator species. Also available to the public are two complementary guide books for protecting vernal pool habitat during timber management (Forestry Habitat Management Guidelines for Vernal Pool Wildlife) and residential and commercial development (Conserving Pool-breeding Amphibians in Residential and Commercial Developments in the Northeastern United States). All of these guides can be obtained by contacting Becca Wilson at Maine Audubon Society (207-781-6180 ext. 222; bwilson@maineaudubon.org).

Finally, the Departments of Inland Fisheries and Wildlife and Environmental Protection have developed a definition of significant vernal pools, a new Significant Wildlife Habitat under the state’s Natural Resource Protection Act, recently approved by the state legislature. Criteria for designating “significant” vernal pools include a) the presence of a state Endangered or Threatened species, or b) evidence of exceptional breeding abundance by amphibian indicator species. Recognizing a subset of vernal pools as “significant” will help state biologists provide guidance on development activities within a critical upland buffer zone surrounding one of the state’s highest value wildlife habitats. Funding for work on vernal pools by the Department of Inland Fisheries and Wildlife comes from the Loon Conservation Plate, the Chickadee Check-off, the U.S. Environmental Protection Agency, and the Maine Outdoor Heritage Fund.

Phillip deMaynadier, Ph.D.
Wildlife Resource Assessment Section
Maine Department of Inland Fisheries and Wildlife

NOTE - This article reflects the views of the author and not necessarily those of the TRC Alliance Team.