When we first moved on to our forestland, we knew little or nothing about how the forest worked with wildlife. New to us was the sight of a four-foot tall snow pile completely littered with conifer cone scales. Of course, it didn’t take long to figure out that the snow was propped up on a pile of slash which the red squirrel was using for a food cache and shelter.
Several decades later, one of my favorite activities is to take a slow hike around our woods a couple days after a snowfall and look for tracks and signs of winter wildlife. I generally find that the most happening places are where there are lots of down logs, shrubs, slash piles and other debris—even though the snowpack hides this very habitable mess.
The small-scale scurrying-around taking place directly underneath the snowpack is much of the reason that coyotes, bobcats, hawks, owls and other predators can stay active in the winter. With old Mom Earth generating heat from below and the snow offering insulation, the narrow little elf quarters between earth and snow become an icy maze of winter activity—what scientists call the sub-nivean space. You will quickly intuit that the Latin name means “below the snow”. The Inuit, experts on snow long before Latin came along, call the crystalline network pukak. With as little as one foot of snow on the ground and air temperatures as low as –50 F, the pukak temperature can be as high as +20 F, a life-and-death 70 degree difference. With less extreme temperatures, even six inches of white stuff can keep the sub-nivean world at temperatures around freezing or even slightly above. Very mild indeed.
Where the ground is covered with grass and brush—or the beneficial litter and deadwood of a forest—the snow does not plaster itself to the dirt. Instead, it is held slightly off the surface, partly through melting, and a highly irregular maze of tunnels, usually 3-5 cm from top to bottom, forms. This labyrinth is used by many 4-, 6-, 8-, and 100-legged creatures. With an active growing season just ended, all the recently-used-to-be green plant matter that has just been shed by both deciduous and conifer plants is lying on the ground and begging for action.
So, the sub-nivean space has a high population of—science name-dropping again—detritivores, or things that eat all that dead stuff. Springtails and mites are two of the most numerous general life forms. Earthworms are also present, and there are many species within these larger groups. Because fungi are also busy breaking down much of this plant matter, some springtail and mite species are present as fungivores. And moving up the food chain, it is obvious that the pukak will also host predators on these creatures. These include spiders, beetles, ants, wasps and centipedes. We may be donning our long-handles during cold spells, but these invertebrates have other ways of coping with below-freezing temperatures. One of the more common strategies is to have up to 35 percent of body weight consist of different alcohols, including glycerol—good old anti-freeze.
The insects and spiders have their predators as well. Shrews, in particular, are avid insect eaters. Northern pocket gophers and voles are mostly vegetarians, but join the shrews as the predominant rodents able to move through the space with the low ceiling. The narrowest sub-nivean spaces where these small mammals navigate are occasionally connected to larger tunnels and entrances, allowing the bigger fuzzy ones access to the action. In a healthy forest, large amounts of dead wood, snags, old root wads and snow-laden green saplings will form a variety of bare-ground spots and access routes into the pukak—and into the cavities in the dead wood itself. These become temporary winter retreats for squirrels, snowshoe hare and grouse, and in turn are often visited by coyotes, bobcats, weasels and marten that sometimes get lucky and find them occupied.
The winter tracks of the short-tailed and long-tailed weasels are easy to recognize and follow. It makes for a fine winter story, watching the tracks disappear below an obvious log or large bush to re-emerge again five to ten feet away and then repeating itself ad infinitum as long as you want to stay with the trail. The long skinny bodies of the weasel family have evolved to adapt to the tiny openings and the forest debris where their prey seek protection. Some predators like great grey owls and coyotes have upped the arms race by developing such keen hearing that they can pin-point rodent noise in the sub-nivean space a foot below, and pounce with enough weight or force to crash through the ceiling, grabbing the prey before it can scurry away.
We’ve heard for many years about the importance of leaving snags and large woody debris in our forests. These winter hikes reinforce how important these elements are—not just for activities like nesting, but especially for surviving the cold-season challenges. Next summer as I stack some slash in a pile or prop a piece of wood up off the ground slightly, I’ll be thinking about the spaces they create and the creatures that will be sheltering there, in sub-nivea.
by John Stuart, Pend Oreille County