By Larry Ely
As we enjoy exploring the natural world in winter, a whole diversity of plant and animal life exists unnoticed and out of sight below the deep snowpack. This unseen “subnivean” world hosts a number of plant and animal species that rely on this unique environment for their strategy to survive our cold northeast winters.
The subnivean zone begins to develop as the snowpack reaches a depth of six inches and at around eight inches begins to stabilize with a steady temperature around 32 degrees Fahrenheit regardless of the air temperature above. Accumulating snow partially melts and refreezes, creating an open space between the ground’s surface and the snowpack. Warmer earth below causes water vapor to rise and refreeze, forming a thin solid roof above that becomes even more stable with a 20-inch snowpack. A similar zone is created around rocks, boulders, low dense vegetation, and logs, and these entries, along with tunnel openings, provide ventilation.
In this world under the snow, microbial life, fungi, and some insects continue to be active, and grasses and seeds are present to support the winter life of small mammals. Some reptiles and amphibians burrow deeper into the leaf litter while meadow voles, short-tailed shrews, and deer mice often live their winter lives within their constructed tunnels and dens. Shrews may also burrow four to twenty inches into the earth when necessary. Each of these creatures weighs under two ounces, and the prolific vole may have as many as seventeen litters per year with females ready to reproduce at one month old. These small mammals are at the bottom of the food chain and are relied upon by foxes, weasels, fisher, bobcat, and coyotes.
Fox and coyote locate their prey under the snow using their keen sense of hearing and pounce upon voles or shrews from above while crashing into their tunnels. Short-tailed weasels or ermine are able to dig into the tunnels for prey through entries from the bases of trees where snow depth is less. Owls also use their hearing to locate these small animals from a distance and swoop in for a kill.
While the ruffed grouse does not live below the snowpack, it utilizes deep snow on cold nights by plunging into the snow and burrowing in. The next day a winter hiker might be startled by one of these overnight visitors exploding from the snowpack. Their exits often leave an impression of their wingspans in the snow.
The subnivean mammals begin to emerge in the spring as they are alerted to the changing season by plants and roots responding to the increased light. They must abandon this world before the collapse or flooding of their tunnels.
Changing climate has caused a deep snowpack to develop months later than in the past, and Dartmouth College’s Department of Geography predicts snowfalls in our region will drop 50 percent by 2050 from today’s levels. The coming winters will offer a challenge to many of our wildlife species to adapt to these changes.
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