The subnivean zone is mostly hidden from humans. We might look at a snow covered field and see this.
|A snowy field with evidence of rabbits.|
Rabbit tracks, feeding evidence, and scat only show part of the story about what is going on in the field. The snow in this picture is more than 12 inches deep. The rabbit that left its tracks was only interacting with the surface. More of the story is buried under the snow.
Try this some time. Wait a few days after a snowstorm and then go find a grassy field that is covered with more than six inches of snow. Look for an area with no visible signs of animals. Take a flat shovel and scrape off the top inch or two of snow from a path six feet long (make sure you don't step in the path of your shovel). You may not find anything unusual at this level. Continue scraping off layers of snow from this path. At some point the path you shovel will probably intersect a horizontal tunnel through the snow. This tunnel will probably be about 1 - 1.5 inches across.
|Found it - a tunnel in the snow|
Once you find one of these tunnels, gently use your shovel to follow the tunnel. Scrape snow from the surface along the direction of the tunnel to expose it to the surface. Be careful not to fill in the tunnel with the snow you are removing. This tunnel will likely travel for many feet in one direction.
|The subnivean world - tunnels within the snow.|
|The subnivean world - cross-tunnels and vertical shafts.|
|A hole dug through 12+ inches of snow to reach the subnivean zone.|
Here is the same image with the lines to show the crust and ice lens.
|The subnivean world - snow crust (blue line) and ice lens (red line)|
This zone can also substantially warmer than the world above the snow. The snow and ice eliminates the effects of windchill to the inhabitants of the subnivean zone - allowing them to retain more heat than they would if they were inches trapped above the snow. Snow is a great insulator and the layers of ice within the snow prevent heat from the earth from rising upward, creating a pocket of warmer air trapped just above the soil's surface. When I was taking these pictures I sunk my shovel down into the soil with no resistance - the ground in this field has not frozen. In areas where the snow cover is thinner (or nonexistant) the two months of cold temperatures have caused the ground to freeze to a depth of 6 inches or more.
So next time you go outside and think that those barren snow-covered fields are devoid of life you will know that there is a whole world going on within and under the snow.
|The subnivean world - tunnels criss-crossing within the snow.|
Welcome to the Sunbivean Zone...