Life Under the Snowpack
Life in the Subnivean Zone, or, down a rabbit hole, literally.
Hey, it’s not January anymore - finally! - and February is on a downward slide already. Into the third week of this month now, there is real hope that Spring is heading this way. This winter in Colorado has been one for the books with deep snow and cold from Fruita to Burlington. High country snow levels are at 120-137% of average and it shows if you travel through the snow piles in the ski towns and plow cuts on the highways. Remember, our two snowiest months are ahead of us still! Whether you see it as a hassle or a playground, this enduring snowpack is a GOOD thing. For reasons beyond water levels in the reservoirs and the Colorado River, the deep snow, seeming to be a white blanket of quiet dormancy, is quite the opposite for life under the snowpack.
The Subnivean Zone - Latin for ‘under snow’ is the layer between the ground and the snow and is full of activity. Once there is 6 inches or more of snow cover, tunnel construction, both natural, in bowed grasses and shrubs, and critter made, begins to form. A network develops of pathways, rooms, storehouses, and nests for living things from microbes to rabbits.
Let’s back up a bit first. The early snows of November and December begin the snowpack. All those light, fluffy flakes build up in inches and feet. Over the coming days, of the snow settling and some temperature changes, the snow goes through a deconstructive (breaking down) metamorphosis where the snowflakes change to rounder snow crystals fusing with the others, creating a tighter construction with less air between. Above this piles the constructive (building up) metamorphosis as more snow builds and in sublimation (changing from solid straight to gas), warm water vapor moves upward from the warmer ground through the snowpack, creating a dense seal that keeps temperatures near the ground right at 32°F (0°C), like your fridge. Now, protected from the deeper cold and winds, the domed critter city becomes busy. Layers of crusty melting and refreezing pile on like a cake as the snowpack builds. The overall construction, if undisturbed by heavy hooves, boots, snowmobiles, and other disruptions, is quite secure for the creatures that move about their snow city underneath. So secure is the main winter critter city that many mice and voles will have multiple litters during these months. Critters as large as rabbits and ptarmigan find shelter in the layers as well.
Enter the owl, fox, coyote, and ermine. Keeping these populations in balance and keeping the bigger critters fed works out well. Owls, with some of the most acute hearing on earth, can pinpoint mouse movement under the snowpack from 75 ft away and break through snow layers to grab an unsuspecting lunch. Fox and coyotes can smell the little guys and pounce up to their hips upside down. Ermine use their slender bodies to enter the tunnels directly. Without their hunting, Spring would emerge with unsustainable numbers of rodents eating all the foliage before it can grow. One piece needs the other pieces to create ecosystem health.
These pieces go down to the microorganism level. The breaking down of organic materials under the snowpack holds in nitrogen that the plant life will need to grow in the spring. This biological activity of ongoing plant decay creates carbon dioxide that is held under the snowpack until it can be reabsorbed by growing plants in the summer. The seeds of summer’s yield are kept in the cooler temperatures of the subnivean, or ‘pukak’ as it is known to the Inuit people. Even butterfly, dragonfly, and other insect eggs are kept in this ‘refrigerator’ state over winter to wake from dormancy in the summer.
In the layer cake of snowpack, nearly 1/3 of the earth’s surface is covered each year. That’s 40 million square kilometers reflecting the sunlight back to the atmosphere rather than the earth absorbing the heat. This ‘albedo’, or amount of reflection, can be 80-90% in snow-covered areas and is key in maintaining viable temperatures for life on earth. Without snowpack, the ground would absorb 6 times more of the sun’s energy. If the snow gets dirty, dust-covered, or removed, the result can amount to earlier runoff and less water overall in the summer months. 120 days or more of snow is ideal for the cycle of the system to remain intact. High country areas hold snow for 180 days or more, doing their part in providing heat reflection, water supply, and safety covering for the plants, insects, critters, and microbes that depend on it.
Spring moves to melt metamorphosis with liquid water moving into the tunnels, sometimes flooding, and the structure collapsing moving the critters back to underground homes or waking with the warming days, and the awakening of plants to photosynthesize in the open sunlight. Yay, Spring!
A fellow blogger also wrote about the tales the snow tells this week. I highly recommend his insights.
Sources:
-https://www.summitdaily.com/news/summit-outside-subnivean-zone-life-under-the-snow/
- https://www.audubon.org/magazine/november-december-2010/life-under-snow#
- https://www.rgj.com/story/life/2021/01/14/beneath-snows-winter-subnivean-zone/4163619001/
- https://www.nwf.org/Home/Magazines/National-Wildlife/2021/Feb-Mar/Conservation/Snow-Ecology
- https://nsidc.org/learn/parts-cryosphere/snow/why-snow-matters
- https://prairieecologist.com/2023/02/20/stories-in-the-snow/