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The Subnivean Zone


As I was looking for tracks and signs of animals in the snowy landscape with Bluff Elementary 5th graders back in January, I noticed a place were small footprints disappeared down a hole into the snow, then reappeared a few feet later, then disappeared a final time into a hole near some bushes.

I assumed it was some kind of microtine rodent - a mouse, shrew, vole or such and started to wonder what the story was here. When did it make those tracks? Was it at night or early in the morning or in the middle of the day? Why would it dig a tunnel into the snow in some places and come out in others? Did it have a nest in the bushes there or was it just moving through? Did any other animals use that tunnel too? My imagination was sparked.

Later on, I looked up some information about who might be using that area between the surface of the ground and the bottom of the snowpack, otherwise known as the Subnivean Zone. And why they might use that space.

I found out that the Subnivean Zone is created when heat from the earth melts some of the snow near the surface, creating a roof of ice on the bottom of the snow pack. There is enough space for mice, shrews and voles to move around freely, searching for food (seeds, nuts, and growing plants) while protected from cold winds and most predators. Some predators, such as owls and foxes, have such good hearing they can find these microtine rodents under the snow!

Once the snow blanket is at least 1 ft deep, it acts as an insulator keeping the tunnels just above freezing for the whole winter. The plants and grasses covered by the snow provide more insulation and provide air shafts for oxygen and other gases to continue to be exchanged under the snow. Light can still pass through the snow, but the level of light is more like twilight even on the brightest days.

As the snow melts in the spring, you will start to see evidence of this active winter world under the snow. Tunnel mazes are uncovered and plants may be stripped of their bark up to the snowpack height.

As long as the snow lasts, go exploring for evidence of the subnivean world and take someone with you to share it with!

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Sullivan County Conservation District

 95 County Farm Rd. Unity, NH 03743

 603-542-9511 x269