SNOW! We love it and we grumble about it. We love it because it provides us recreation and a beautiful landscape. We grumble about it because of slick roads, slippery sidewalks, overloaded trees, and cold. After years of little or no snow, I have a sense of relief that snow is blanketing the mountain again and hopefully there will be fewer fires. Skiers are relishing snow-covered runs, exclaiming “It’s fabulous.” Snow is an amazing gift of nature and one we take for granted. But after years of drought, I discard my negative thoughts about snow and ask “What is the real importance of snow to an ecosystem?”
Ecologically in the Northern Hemisphere, snow is important. Rain can dampen the earth but snow provides for recharging underground aquifers and streamflow. The aquifers store trillions of gallons of freshwater used for drinking water. Streamflow in an arid environment is important to recreation, agriculture, and drinking water. In some western states snow can make up 80% of the annual precipitation.
I wonder and marvel at the dynamics of snow in our environment. Long ago in high school, my favorite biology teacher commented on the whiteness of now. It coats everything in a fresh white blanket. We yearn for “White Christmas” and the weatherman will call it the “white stuff.” So why is it white? She made me curious.
Here is the scientific explanation: “Snow reflects all the colors; no, it doesn’t absorb, transmit, or scatter any single color or wavelength more than any other. The color of all the light wavelengths combined equally is white.”
But as an ecologist, I really want to know how snow makes a difference to the ecosystem and all its creatures. Snow can be a harsh environment and lead to death. But for every negative in the environment there is a positive. So what is it?
Snow plays a role in temperature regulation. Snow cover reduces net radiation and acts as a heat sink. It inhibits soil warming until the snow melts but is a good insulator keeping the soil temperature near 32 degrees Fahrenheit.
We often think of winter as a time when everything is dormant or dead. But our coniferous forests still photosynthesize on warm days and life goes on beneath the snow cover. Insects, fungi, and mammals busily carry on their activities because of the insulating properties of snow. Plants covered with snow are protected from drying out.
Snowpack that accumulates throughout the winter insulates the soil, keeping it generally unfrozen. This allows the unfrozen soil to absorb water from melting snow. In the Eastern states, a ten-inch snowpack covering one acre can hold 30,000 gallons of water! (extension.psu.edu). The humidity of the snow/soil environment provides a “greenhouse” effect allowing plants to photosynthesize and grow even before the snow is melted.
The insulating power of snow is also important in other ways. Without snowpack, very cold temperatures can freeze the soil deeper and deeper. Root systems within the frozen zone can be damaged, weakening or killing the plant. The milder temperatures and sun warm the exposed and frozen soil, causing heaving and root breakage.
Studies done at the Hubbard Brook Experimental Forest in New Hampshire found that forest productivity increased with snow cover. Without the insulating cover, deciduous trees didn’t take up nutrients or water as quickly as those with a good snow cover (Lynda Mapes, Snow: Winter’s Gift to the Forest).
The temperature regulation provided by snow is important in the annual growing season and the reduced chances of fire during spring, summer, and fall. Wildfires can denude acres of land of trees, changing the dynamics of the ecosystem. No snow means higher temperatures to the soil and drying vegetation during the winter months, contributing to fire danger.
Studies have shown that there is a correlation between fire and drought. Within a dry environment, the downed woody and grass material can ignite and the fire can spread rapidly. But the spread of the fire will also depend on the dryness and density of the standing vegetation. The moisture of fuels can change some with rain; however, the slow percolation of snow melt better saturates the soils and vegetation. Using LANL’s Weather Machine, Figure 1 illustrates the snowfall the winter before our major fires. The average annual precipitation for the Los Alamos area is 18.86 inches of rainfall and 56 inches of snowfall. Note that during each of these periods the snowfall was significantly lower, creating a drier forest environment.
Another advantage to snowpack is for small animals. Voles, mice, and other critters are protected from severe temperatures. The zone between the snow and the soil is called the subnivean zone. This zone is not solid because vegetation creates air-pockets. The snow insulates and keeps the temperature around 32 degrees, even though the surface temperatures may be much lower. The small animals are not only protected from predators, biting wind, and cold temperatures, but can access their stored food. The subnivean zone allows them to make tunnels connecting the air pockets formed under the snow. Other animals, like foxes, are adapted to hear these small creatures in their tunnels and then find them.
Because of winter weather, some animals hibernate or migrate, but others adapt to the snowy environment. In our mountain area, pikas busily store food during the summer, but in the winter they are deep in tunnels beneath the snow and rocks, giving them access to their stored food.
Some facts about snow:
- Glaciers cover 10% of the planet’s land area.
- In the Northern Hemisphere, historically, snow falls each year on one square mile out of two.
- In the west 75% of the water used for irrigation comes from snow.
- Snow powers the great rivers: the Colorado, the Rio Grande, the Columbia, the Missouri
- Snow forms around particulates in the atmosphere and drags them to the ground, cleansing the atmosphere.
Water—rain, snow, rivers, ponds are the lifeblood of the West and our semi-arid environments. John Wesley Powell, an early explorer, said: “In the whole region, land as mere land is of no value. What is really valuable is the water privilege.” Snow is water that powers our environment and keeps our ecosystem healthy.
So next time we grumble about shoveling snow or driving on slippery roads, let’s remember that snow is amazing and provides for diversity of life in this arid land.
Figure 1: The snowfall the winter prior to large fires on the Pajarito Plateau.
In Praise of Snow. http://www.civil.utah.edu/~cv5450/intro.html