6 minute read
Ecology of Snow
THE ECOLOGY OF SNOW
words :: Leslie Anthony
By the time you read this, the freezing-level roller coaster of autumn may have already hastened the arrival of a winter wonderland to your neck of the woods. While that first snowfall might be short-lived, however, seeing the land transformed by a curtain of snow and sudden snowbanks brings more to mind for some of us than the surety of awesome skiing. There’s also the little-known ecology of the white stuff to consider—especially in these days of duelling biodiversity and climate crises.
Across landscapes and over time, changes in snow-cover regimes and snowpack structure have widespread impact as an ecological factor, as well as on human well-being and economic issues like water availability, agriculture, transportation and winter recreation (did I already mention skiing?).
As snow lovers, it should be incumbent on us to understand the massive influence snow exerts on Earth’s climate through its properties of high reflectivity, atmospheric cooling, insulation and water storage— each of which has outsized importance to the planet’s biological, hydrological and nutrient-cycling systems. Back in 2007, when the United Nations Environment Programme released a white paper on snow (the humour of which I’m sure they appreciated), the extent of snow cover in the Northern Hemisphere had already decreased 1.3 per cent per decade over the previous 40 years. At the time, climate models projected significant further decreases in snow cover by century’s end, with reductions of 60–80 per cent water equivalents in most midlatitude regions, reduced ice (but increased precipitation) in the Arctic, and rising snowline for many mountain regions. All of this is not only well underway 50 years earlier than expected, but rapidly accelerating.
Although the importance of snow as an ecological factor was recognized by science early in the 20th century, it wasn’t until the 1950s that the way snow shaped alpine plant communities, for instance, was analyzed. In the new millennium, experiments with snow have explored the effects of snow-cover depth and duration on plant communities and ecosystem processes. More recently, snowcover models have been applied to ecological issues like near-ground temperature regulation.
Snow’s high albedo (that is, reflectivity) reduces net radiation, and also removes energy from the atmosphere in the form of heat. Thus, counterintuitively to some, snow both inhibits soil warming by preventing microbiological activity that would raise temperatures above 0˚C, and insulates, reducing temperature extremes in the undersnow zone known as the “subnivean cavity” where small mammals like voles, lemmings and mice remain active and protected from predators. In spring, with higher sunlight levels penetrating thinning snowpacks, plants in the subnivean’s humid snow greenhouse can start growing weeks before plants covered by deeper snow.
As a physical medium, snow can both enhance landscape access for certain animals or inhibit access for others by being too deep or too soft. Snow can support animals like birds and small mammals with little trouble, but larger mammals like deer and moose experience critical snow depths above which they can’t move. This is why whitetailed deer in Ontario have been described as “yarding up” in lowsnow areas since the days of early settlement. Deer yards can be as small as a few hectares or as large as many square kilometres. Managed and mismanaged for at least a century, they’re better referred to as “deer winter-concentration areas.”
Snow itself is also a habitat for other life forms. The array of organisms found in and on both seasonal snow cover and glaciers include ice worms, bacteria, viruses, fungi, diatoms, rotifers, tardigrades, springtails, flies, spiders and algae that, with up to 5,000 cells per cubic millimetre, can colour snow red, blue or green. When organic matter becomes too abundant in snow it reduces its albedo, resulting in accelerated local melt and nutrient accumulation. You can most readily see this in spring: As snow melts, organic matter concentrates on the surface along with an entire insect food chain that together darken the snow and speed up the melt. With climate change this is happening earlier and faster in many places.
Snow also accumulates debris from field and forest (e.g., seeds), plant nutrients (e.g., nitrogen), and atmospheric pollutants during the winter to be released or redistributed by spring melt; nitrogen release, for instance, results in a flush of moss growth, but in higher concentrations can also have negative effects.
Tundra’s typically patchy spring snow cover affects both the breeding of ground-nesting migratory birds and the distribution of plant communities. Plant associations characteristic of hollows where snow accumulates have short growing seasons and are waterlogged after thaw, whereas those on wind-exposed ridges are more droughttolerant. Traditional knowledge among the Eurasian subarctic Saami people describes the influence of snow on the vertical distribution of lichen species on the trunks of birch trees, where one species grows exclusively above the winter snow line, another below it.
Most importantly, mountain snow cover is a critical source of freshwater, changes to which can have indirect effects such as increased intensity and size of wildfires because of moisture stress on mountain forests, or impacts on fish like salmon and steelhead that require high freshwater stream flow for migration to oceans/lakes after hatching. The more frequent winter thaws of our changing climate can also affect ecosystems, reducing snow insulation and increasing the potential for frost to penetrate into the soil and damage plant roots, or by sparking microbial activity that releases greenhouse gases like methane at a time when a plant’s uptake of carbon to offset this process cannot happen, leading directly to increased atmospheric carbon.
The impacts on snow cover also apply to agricultural crops. Gradual changes, as well as extreme snow events, can have a strong impact at the start or end of the growing season and change the economic cost-benefit of raising certain crops.
If it suddenly seems like snow has a more extensive resumé than as a simple medium for human fun, it does. So maybe the next time you’re out enjoying a big snowfall you could spare a thought for how important this phenomenon is to literally everything it touches.
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