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Vernal pools are small, isolated wetlands
that hold water on a temporary basis, most often during winter and spring.
They might be as small as a living room or as big as a football field, and
can occur deep in the forest, in open wetlands, and in low spots in
land. They are filled by the spring's rising water table or snow
run-off. Because they don't have an above-ground outlet for water, they
are usually gone by late summer.*
Vernal pools are very important to the life cycle of many amphibians, as they are too shallow and short-lived to support fish that would eat
the amphibian eggs or larvae. Vernal pools and their adjacent upland
habitats encourage biodiversity by supporting an abundance of plants,
invertebrates and vertebrates not found in other areas.
Species that depend on vernal pools for
successful breeding include fairy shrimp (inch-long crustaceans with a
lifespan of just a few weeks); spotted, marbled and Jefferson
salamanders; eastern spadefoot toads; and wood frogs. A wide variety of
other forest animals, including birds, turtles, snakes, and small and
large mammals also use these pools for feeding and resting. In addition,
these "sylvan gems" are aesthetically pleasing, with moss-covered  logs,
delicate hues of greens and browns, and dappled sunlight shining through
forest cover.
However, because they are small, hard to
identify, and subject to limited regulation, they are often impacted by
development. As a result, vernal pools - and the species that depend on
them - are rapidly disappearing.
Many vernal pool amphibians go back to
breed in the pools where they were born. If the pool is disturbed or
destroyed by development, the amphibians show little tendency to relocate.
It is also important to remember that these animals rely on both vernal
pools and connecting upland terrestrial habitats for survival, spending
about 11 out of 12 months each year in adjacent uplands, forests and
wetlands.
Even a relatively small degree of
development (25% of surrounding critical terrestrial habitat) can
negatively impact vernal pool wildlife. For example, one study done in
Massachusetts found that when 25 acres of upland forest next to a vernal
pool was cleared, the pool's wood frog population became locally extinct,
despite a 150 foot wide forested buffer around the pool and a forested
wetland corridor adjacent to the pool.
The most valuable vernal pools are:
- ecologically significant due to size and the length of time they hold water;
- have state-listed or vernal pool species present/breeding; and
- are surrounded by intact, undeveloped critical terrestrial habitat.
Vernal pools, like Atlantic Cedar Swamps, are critical habitats that we must continue to work together to protect. Mechanisms include acquisition by a conservation organization like a land trust; conservation easements; employment of best management practices to integrate design, engineering and natural resource protection into developments; zoning/ordinances; and last but not least, voluntary stewardship programs by landowners.
*According to A Field Guide to the Animals of Vernal Pools by Kenney and Burne, "many of our larger vernal pools persist for several years before drying". And according to Elizabeth Colburn's book Vernal Pools: Natural History and Conservation when defining the hydrology of vernal pools, states "they dry up annually or every few years - standing water either disappears completely, or water levels drop substantially durning the summer, exposing most of the pool bottom and retaining only a fraction of the peak volume;". |
