Imagine this… You awake to another typical winter day where the dim light filters its way into your home. Your thermostat reads a steady and consistent temperature in spite of the frigid temperatures and blustery weather of the outside world. Your food pantry, just a quick walk down a long hallway, is stocked with all your favorite foods that you carefully stored up from the summer. In spite of the thick, protective walls and roof of your home, you keep a careful watch for potentially life-threatening danger while conserving your limited energy.
I know what you’re thinking… no, this isn’t another typical day of working from home during the pandemic. This is the story of winter survival for a small animal living in the subnivean zone.
The subnivean zone is the boundary between the ground and the bottom of the snow pack. It is home to many small creatures like mice, voles, moles, shrews, insects, spiders, fungi, and plants during the winter. The winter is challenging for most organisms for a variety of reasons including the cold temperatures, short days/lack of sunshine, conserving energy, lack of water to drink (that isn’t frozen), and snow. The subnivean zone can help organisms battle many of these challenges and survive the winter.
Cold: The subnivean zone starts to form in autumn when the snow starts to pile up. Once the snowpack reaches 6 inches (15 cm) deep, it acts like a thick blanket and insulates the subnivean zone, keeping it a consistent and manageable 32°F (0°C) throughout the winter.
Radiation: During the winter, the days are shorter and the amount of sunlight that plants and organisms receive is reduced. Although the snow pack does block some of the sunlight, enough solar radiation trickles all the way down to the subnivean zone! This allows for seeds to germinate and plants to grow and make their own food under the snow.
Energy/Snow: It takes a lot of energy to stay warm, move around, and survive in the winter. The best way for organisms to refuel is by consuming enough food and calories. For most organisms, the snow buries their food sources making it hard to refuel. Small organisms living in the subnivean zone build vast tunnel networks, allowing them to move around safely and continue to forage for food throughout the winter.
Water: Creatures living in the subnivean can’t just hop over to a nearby river or pond to grab a quick drink of water in the winter because these water sources are likely frozen. Since temperatures in the subnivean zone hover right at freezing temperature, some liquid water is present in the form of melting ice and puddles. This water is accessible for both plants and animals to access for survival.
Although the subnivean zone is the key to survival for many organisms, life under the snow is not without its hazards and dangers. Carbon dioxide accumulation, from plants and animals respiring, can make it hard for creatures to have enough oxygen to breath. Once the snow starts to melt in the spring, tunnel networks in the subnivean zone can flood. As a result, many animals have to relocate, making themselves vulnerable to predators and food scarcity. Predators, like weasels/ermine, foxes, and owls, can pose a threat from both under and above the snow. Weasels/ermine use the tunnel networks created by small animals living in the subnivean to hunt for prey. Foxes and owls can hear small animals moving around under the snow and pounce through the snowpack to the subnivean to capture their prey.
Next time you find yourself skiing down the slopes, digging a snow pit, building a snow person, or snowshoeing down a peaceful trail, imagine what your life would be like below the snow. Keep an eye out in the spring for a peek into the subnivean zone when the snow starts to melt. Look for evidence of the winter world of tunnels and survival left behind by all the creatures that call the subnivean home.
Carrie Anderson is the Environmental Leadership Coordinator at Walking Mountains Science Center. She is often seen exploring the wild places, trails, and ski runs in the White River National Forest and beyond.
Adirondack Almanack. (2014, December 31). The Subnivean Zone: Life Under the Snow. Retrieved from Adirondack Almanack: https://www.adirondackalmanack.com/2014/12/the-subnivean-zone-life-under-the-snow.html
Halfpenny, J. C., & Ozanne, R. D. (1989). Winter: An Ecological Handbook . Boulder: Johnson Publishing Company.
Rocky Mountain National Park Environmental Education Staff. (2013, April). Winter Ecology Teacher Guide. Retrieved from https://www.nps.gov/romo/learn/education/upload/Winter-Ecology-Teacher-Guide-for-web.pdf
Yosemite Conservancy. (2019, February 20). Getting in the (Subnivean) Zone . Retrieved from Yosemite Conservancy : https://yosemite.org/getting-in-the-subnivean-zone/