Look to the forest floor for some of the first signs of changing seasons, writes Shelby Perry, Stewardship Director of Northeast Wilderness Trust
In the first week of March I start, even though I know it is too early, but the anticipation pulls me like a magnet. In my snowshoes I climb the hills outside of town, follow the folding topography to the low spots, and check on them regularly. The effort is not wasted, for I get to enjoy other harbingers of spring as I go. At first the signs are subtle: slight swelling of buds, the staggering tracks of skunks in soft snow, heat wells around the trees in the snow pack, a change in bird song. Then the more obvious signs begin, and my excitement grows: bear tracks, drumming grouse, bits of green, mud! By the time I trade in my snowshoes for mud boots my path to the vernal pools is well traveled.
Vernal pools begin to come to life in the Northeast anywhere from mid-March in the south, to as late as May in the north and higher terrain. In central Vermont, where I live, activity in the pools usually gets going around mid-April, though this year could be a bit later because of the deep snow and lingering low temperatures.
What makes a pool a vernal pool? Two things, really: first it fills with water in the spring and dries up completely by late summer; second, it has no permanent inlet or outlet. These characteristics are important because generally this means that the pool cannot support a population of fish. Fish gobble up amphibian eggs and larvae, so pools without these voracious predators give the baby amphibians a better shot at making it to adulthood.
What makes a vernal pool amazing? So many things! They are positively teeming with life. Eastern toads, wood frogs, eastern newts, leopard frogs, spotted salamanders, fairy shrimp, fingernail clams and more can inhabit a single pool no bigger than a parking space simultaneously when activity is at its peak. Many of the frog and toad species call from the pools, and the chorus can be heard from quite a distance if you approach quietly. If they hear you coming first though, the calls will cease and not begin again until you leave.
Usually the first arrival at the pool is the wood frog, and they are a fascinating case study of life in the pool. Wood frogs over-winter in the leaf litter at the ground surface. They concentrate sugars in their blood just before winter, a process which allows them to freeze solid for over four weeks at a time without sustaining the kind of cellular damage that kills most living things that freeze. This adaptation allows them to become active as soon as the ground surface thaws in the spring, and as soon as they can move they make their way to the pools, mate, and lay eggs.
The eggs that don’t end up in the belly of a newt, bird, or mammalian predator hatch in a few weeks and the pool fills with tiny tadpoles. Nibbling on leaves and algae, the tadpoles start out mostly vegetarian. Remember though, these pools have no permanent inlet, meaning that when the rains and meltwaters of spring subside the pools begin to shrink. Naturalist and ecologist Bernd Heinrich once conducted an experiment where he raised wood frog tadpoles in a tank, as long as he kept plenty of fresh water and food for the tadpoles, they stayed tadpoles, for about 8 months! As soon as he let the water level drop though, and things got a little bit crowded, the tadpoles turned on each other, and swiftly metamorphosed. Heinrich concluded that when conditions in the pool concentrate the tadpoles, the resulting cannibalism triggers metamorphosis into frogs.
Many of the mechanisms that have evolved to allow vernal pool species to survive, including how metamorphosis is triggered in wood frogs, are still poorly understood. There is so much left to learn from these fascinating little creatures, but sadly amphibian populations are declining around the globe. A mind-boggling array of factors, from road salt to climate change, habitat fragmentation to invasive pathogens, are all contributing to the detriment of our amphibian neighbors. The conservation of large, intact blocks of wild forest protects the stage on which the drama of amphibian life unfolds.
Northeast Wilderness Trust is currently working to protect the Bridgewater Hollow Bramhall Preserve just outside of Woodstock, VT. The property hosts at least two productive vernal pools, and maybe more. Conservation of the acreage surrounding these pools as wilderness is the best possible outcome for their springtime inhabitants. Wilderness means no skidder treads will ever crush the frozen frogs in winter, no new roads will crisscross their habitat, and no chemicals used to control weeds or melt snow will ever foul the waters of the pools.
Please consider making a tax deductible gift today to support the conservation of the Bridgewater Hollow Bramhall Preserve as wilderness. The frogs and salamanders will thank you!
Keep It Wild,