From Winter to Spring: A Vernal Pool Emerges
- Julie Reiff
- Apr 14
- 2 min read
By Linda Ray
In the woods up behind my house, there is a beautiful, almost hidden, vernal pool. It is surrounded by dense forest and has spent all winter under a few feet of snow. Appearing as a slight depression under a white blanket, it was so very quiet and seemingly empty. But beneath the insulating cover of snow lay a subnivean world, both in and around the winter pool.
What is a subnivean zone? It is the place between the earth’s surface and the base of a snowpack. The snowpack insulates to slightly above 32 degrees, trapping ground heat and creating a microclimate between soil, mud, leaf litter, and snow. Insects crawl around in the duff (leaf litter), living alongside fungi and microbes. Other invertebrates such as fairy shrimp and small snails may become frozen under ice if the pool still had water when winter temperatures arrived. This is their comfort zone in winter.
Amphibians such as wood frogs and spotted salamanders, having left the pool after spring breeding, spent the winter in their upland home in a state of brumation or deep winter long hibernation. This survival process is part of their natural cycle, and they can remain in this state for six months or more. They winter below the frost line in leaf litter, nooks, and old burrows.
“What appears silent and frozen in winter becomes a vibrant, essential nursery for life when the vernal pool returns each spring.”
What appeared quiet and empty in February will transform in April. In early spring, the vernal pool begins to fill again with snowmelt and rain. When temperatures reach 40 degrees or more at night, brumation begins to cease and resident creatures wake for another boisterous spring. Wood frogs and spotted and blue salamanders are obligate breeders who return to the vernal pool where they were born. Vernal pools, temporary and fish free, are the most advantageous for breeding, egg laying and larval development. The average spring migration from woods to pool is around 400 to 650 feet.
Vernal or “spring” pools play an important role in the health and balance of forest ecosystems. This is recognized by law under the National Resources Protection Act and supported by the Maine Department of Environment Protection. Without protection, loss of significant vernal pools and the area around them would lead to amphibian species decline, a decrease in diversity, and loss of a food source for many other animals.
Last April, I was fortunate to borrow a pair of hip boots from a friend and step into the vernal pool in my back woods. I was fortunate, first, because I didn’t fall in and, more importantly, because of the up-close experience of witnessing this glorious spectacle of nature. Various salamander and frog egg masses abounded, assuring their place in the ecosystem and food chain. It was a very reassuring sight.
All photos by Linda Ray
Sources:
Burne, Matthew R. and Kenny, Leo P. Afield Guide to the animals of vernal pools. Massachusetts Division of Fisheries and Wildlife, Natural Heritage and Endangered Species Program and Vernal Pool Association, 2009
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