Vernal Pools: An Earth Day Celebration of Wildlands
I didn’t know anything about vernal pools or that there were two of them in the woods east of my house until I had a lightning strike burn down a tree into its roots and turn into an underground fire one August. The following spring, I ventured out into the woods to see how the site of the fire was recovering and was surprised to find myself standing at the edge of a small pond that hadn’t been there in August.
A vernal pool is a depression in the earth that is not permanently connected with other bodies of water. The depression fills with water at certain times of year (usually in spring – thus the name “vernal,” which is based on the Latin word for spring) and dries up at other times. Vernal pools in my native region of New England are usually found in woodlands. Typically they fill with water from snowmelt in spring and slowly evaporate during the dryer months of summer. They may also fill from heavy rains or from a rising water table during particularly wet periods. How much water is in a vernal pool can vary from one year to another depending on the amount of snowfall and rain. One of the two pools in the woods just east of my property line is quite small and typically dries up by late summer. The other is much larger; in wet springs, it can cover more than a quarter mile out to the nearest road, and it sometimes contains water all summer long.
Because these bodies of water are temporary (all vernal pools dry up at least in dry years) and are not typically connected to larger bodies of water, fish cannot survive in them. This makes them prime breeding grounds for amphibians like frogs, toads, and salamanders that are vulnerable to fish predation. As declining populations of amphibians have become a cause for concern, the ecological value of vernal pools has become more apparent.
Vernal pools are themselves vulnerable to being destroyed by property development. The United States Environmental Protection Agency (EPA) estimates that 90% of California’s vernal pools have already been lost. In 2006, my home state of Maine passed legislation protecting a subset of vernal pools called “Significant Vernal Pools.” To be classified as “significant,” a vernal pool must have abundant populations of certain indicator species (fairy shrimp, blue-spotted salamanders, spotted salamanders and wood frogs) or must be critical to the life cycle of certain rare, endangered or threatened species. Thus far, between 20% and 25% of Maine’s vernal pools have been classified as significant vernal pools. This classification is controversial because the law not only protects the vernal pool itself but also designates a “zone of consultation” on any land within 250 feet of a significant vernal pool. Special permits are required to build in this zone of consultation, and some landowners regard this as unfair “taking” of their property. In the face of this controversy, the University of Maine and Maine Audubon have moved ahead with a program of education about vernal pools and assistance to local municipalities in mapping the vernal pools within their boundaries. Their 100+ page Maine Municipal Guide to Mapping and Conserving Vernal Pool Resources is a wonderful source of information.
As I’ve learned more about vernal pools, I’ve developed a special appreciation of these quiet oases near my house. I make a point of walking out into the woods to visit the pools several times each year, and both their beauty and their contributions to the local ecology enrich my life. They make it possible for me to be serenaded on warm spring nights by a chorus of spring peepers, and they provide breeding grounds for the toads and dragonflies that are regular visitors to my garden.