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Vernal Pools: An Earth Day Celebration of Wildlands

April 23, 2013

vernal pool2I 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.

dry vernal poolBecause 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.

vernal pool breeding signsAs 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.

20 Comments leave one →
  1. April 23, 2013 10:24 am

    Fascinating topic.
    The photo at the top of the blog is stunning.

    • April 29, 2013 5:05 pm

      Thanks, Allan. You can imagine how magical it was when I first stumbled across this pool in the woods. I had been living in the house for several years and never knew it was there!

  2. April 23, 2013 12:05 pm

    Thanks for the information, I did not know about this.

    • April 29, 2013 5:08 pm

      It’s a pretty neat phenomenon, Jason. Once I knew about them, I started thinking back to childhood and realized that I had encountered some vernal pools but didn’t know what I was looking at.

  3. April 23, 2013 1:33 pm

    Nice post Jean. As a past member of our town’s Conservation Commission, we often were looking to preserve these resources. Our state has gotten pretty good at limiting development within buffer zones. However there is a pretty convoluted process to certify Vernal Pools.

    A town over closes roads on key spring nights that go through these sensitive areas to minimize the carnage caused by cars.

    • April 29, 2013 5:10 pm

      Reed, There are warm spring nights in my neighborhood, especially during or after a rain, when you can’t drive down the local roads without encountering hundreds of little frogs trying to hop across to the other side. I had never associated this with the vernal pools, but of course….

  4. April 23, 2013 7:11 pm

    Fascinating post Jean. I’ve never heard of these before or would have realized the significance. As I was reading though I was thinking about a depression on our property that holds a good amount of water each spring.

    • April 29, 2013 5:11 pm

      Marguerite, Sounds as though you have your own vernal pool. Around here, they tend to get water in them again in the rains of late fall and then freeze over for winter.

  5. April 24, 2013 9:53 pm

    Well we have these in the wild area behind us and in my garden which is why I turned them into rain gardens with plants….fascinating and yes the toads and frogs love them and the birds bath in them. Due to being close to see level, in heavy clay soil, lots of rain and snow and living near swamps we have these areas that fill with wildflowers once they dry later in spring.

    • April 29, 2013 5:15 pm

      Donna, They’re a special treat in my area because the local “soil” is mostly sand and doesn’t retain moisture at all. For a while, I entertained the idea of creating a path through the woods to the smaller vernal pool and creating a garden on the edge consisting of water-loving plants that I can’t grow in my garden. Turns out, though, that neither pool is on my property; they’re just on the other side of the boundary line.

  6. April 25, 2013 3:49 am

    We too have what I call a “seasonal pond” on our property. Just planted around the edges and I’m really looking forward to the wildlife developing there. It may not be a great sight when empty but it supports a lot of animals and is very important for their survival.

    • April 29, 2013 5:25 pm

      Annette, For a while I had dreams of planting some water-loving plants at the edge of mine, but it turns out to be on my neighbor’s property. Because the two near me are in the woods, they tend to just blend into the rest of the woodland when they’re empty.

  7. April 25, 2013 9:07 am

    Great post. We have lots of water on our property including the frog pond which became a beaver pond a couple of years ago. There are several dug wells, some of which go dry early in the season, but in spite of water running just below the surface I have yet to locate a vernal pool. I shall keep searching.

    • April 29, 2013 5:27 pm

      Pat, I hope you find one. I feel as though it is a magic place hidden in the woods.

  8. April 27, 2013 3:53 pm

    Hi Jean, I really like your first photo of the vernal pool and reflections in the water. I’m glad these niche habitats are now in the “conscience” and are being protected. Thanks for writing about them, it was very interesting to read and learn.

    • April 29, 2013 5:29 pm

      Thanks, Sunil. It is good to have people being educated about the importance of habitats like this instead of seeing them as swamps that need to be filled in.

  9. April 27, 2013 6:35 pm

    Once we get to False Bay we’ll be supporting the leopard toads. Our seasonal ponds will be filling now, as we go into our rainy season.

    • April 29, 2013 5:49 pm

      Diana, From what I’ve read, these seasonal pools are common in two kinds of environments — Mediterranean climates like yours, and glaciated landscapes like mine. I love the fact that, on opposite sides of the globe, we experience this same phenomenon at the same time of year, but for very different reasons.

  10. April 29, 2013 12:28 pm

    Vernal pools, how very interesting and informative Jean, bet you haven’t heard of Vernons pools though.

    • April 30, 2013 12:54 pm

      LOL, Alistair, I had to look it up! I’m not much of a sports fan or much of a gambler (except to the extent that all gardening is a form of gambling 🙂 ).

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