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Nature Notes: Vernal Pools

Ed Robinson
March 28, 2013

Under the snows of winter, Mother Nature is preparing a seasonal treat for us as we eagerly anticipate mud season. Ok, I was stretching things a bit since mud season is generally viewed as the worst time of year in Maine. But the snow pack and rains that will follow are vital parts of the process for recharging unique bodies of water known as vernal pools (from the Latin word “vernus” meaning “of Spring.”).

vernal pool among trees

Vernal pool (Kobosev3179 iStock photo)

A vernal pool is a small, seasonal wetland that often forms in shallow depressions over bedrock or clay-containing soils. Vernal pools lose a considerable amount of water to evaporation in drier parts of the year and often dry up completely. Not surprisingly, the cyclical fluctuation of water levels has a significant impact on the distinctive plants and animals that inhabit these pools.

A vernal pool, because of its periodic drying, does not support breeding populations of fish. This allows other species to flourish, where they have adapted to the conditions of the pool. It is common to find large egg masses from salamanders and wood frogs. My friend Rob Bryan notes that juveniles from these eggs are in a race for life. They are born with gills but must mature and develop their lungs before the pools dry up. Tiny crustaceans called fairy shrimp live their entire life cycle within a few weeks, leaving behind egg cases that lay dormant through dry and freezing periods before hatching in the next year’s waters. A pool may also have specialized plant species that grow annually, thanks to seeds left behind that can handle extended dry spells.

Walking through the woods, it can be easy to overlook vernal pools since they are often visually underwhelming. But time your visit well, and you will be amazed at the life emanating from these special habitats. Birds such as ducks and raptors use the pools as a source of food and water, and mammals large and small will stop by for a drink or something nutritious. Twice in recent years I have been at our old farmstead in New York State when salamanders were visible during their one to two day breeding season. I was amazed to see dozens of these creatures that spend the rest of their year well hidden in the earth or under rocks and decaying logs.

Vernal pools have long suffered from man’s ignorance and neglect, and many were destroyed in the rush of land development. Fortunately, in recent years, numerous groups have taken action to educate the public about these tiny ecosystems. Not only do vernal pools offer essential habitat for many species, they also play a role in erosion control and water quality. In 2007, Maine launched a statewide effort at the community level to survey and map significant vernal pools to encourage better development planning and improved conservation efforts.

Visit a local pool on a warm spring evening and you will be rewarded with a vibrant chorus of frogs and song birds. You can find verified vernal pools at HHLT’s Hackett Land Preserve and at the headquarters of the Land Trust, both on Route 123.

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