“They’re not dead, dear—they’re just sleeping”

🕔Dec 07, 2010

Maybe the hardest notion to accept about winter is that it is so alive. Beneath the bark of the leafless tree, under the frozen moss, in all the little crevices of winter, there is life! (Peter Marchand, Life in the Cold).

As the leaves turn golden and fall to the ground, as ice crystals form on ponds and lakes, as the temperature drops, it’s hard for many of us to think about going outside to look at nature’s wonders.

Apart from watching the occasional moose or deer passing by, or admiring the birds at our feeders from the warmth of our kitchens, most of us think of nature-watching as something best left until spring. But there’s lots going on out there in the cold months, and looking for it can enrich our winter recreation.

Survival strategies
Have you ever wondered how animals and plants survive at temperatures below -25ºC? Some animals, like bears and marmots, avoid the problems of winter by hibernating in cosy dens in a state of suspended animation. Frogs and toads bury themselves deep in soft mud and produce a type of internal antifreeze to prevent their cells from freezing. But other animals have to develop strategies to resist all the hardships that winter has to offer as they search for food and shelter.

Spiders, shrews and voles manage to stay active all winter long by living in sub-nivean (under-snow) spaces. Snow has excellent insulating properties. In fact, for many living creatures, having a 40-50 cm blanket of snow over their heads is critical for survival. It surprises many people to learn that the temperature at ground level, beneath the snow, is at 0º Celsius.

Snowshoe hares, lynx, deer, moose and wolves put on thick fur coats and rely on forests for additional warmth and shelter. Winter-resident birds have soft downy feathers close to their skin that they fluff up, trapping air against their warm bodies. Some have bare legs and feet that don’t freeze because warm blood from the body flows down the legs and warms the cold blood running up the legs from the feet—a counter-current heat exchange system. Ptarmigan, on the other hand, have feathered feet and legs. The feathers protect them from the cold and also act like mini snowshoes, giving them buoyancy on the snow. In really cold weather ptarmigan will bury themselves in the snow, then erupt in an explosion of flakes and feathers when an unsuspecting snowshoer or skier ventures too close.

Carnivores can eat other animals (shrews eat spiders, lynx eat snowshoe hares), but many of our winter animals are heavily dependent on plants for food. Most of the really succulent plants have died back or are protected under the snow, leaving only woody shrubs and trees above the surface. How do these plants survive through the winter? Why do many of our trees and shrubs lose their leaves, but others—like the conifers—don’t?

How trees survive the winter
Years ago I was asked to take some visitors from the Philippines on a nature walk in early spring and they asked why so many of our trees had died. They sure looked dead but were simply avoiding their two biggest stressors—desiccation (drying out) and low temperatures. Many deciduous trees and shrubs (e.g. cottonwoods) have big, broad leaves through which a lot of water is lost. Leaf-fall reduces the plant’s need for water at a time of year when liquid moisture is scarce. These big leaves would also allow snow to accumulate, causing branches to break under the weight. With leaf-fall, the tree is spared this damage.

Trembling aspens have another coping mechanism for northern survival. Their bark contains chlorophyll and contributes up to 15 percent of the total photosynthetic surface area. They are thus able to produce their own food (sugars) in their bark after leaf fall and well before the new leaves appear in the spring—a fact well-known to moose who can smell the sugars in the bark and strip it off with great relish in late winter/early spring.

If leaf fall is a good strategy, why don’t conifers suffer snow damage? The spire-shaped form of conifers helps them shed large accumulations of the white stuff. Nonetheless we often see huge snow build-ups on conifers at high elevations. This can be both good and bad. The weight can cause severe damage, but the snow blanket does insulate against low temperatures. The really severe damage, especially to subalpine trees, is caused by abrasion of exposed trees by wind-blown ice particles. In addition, conifer needles have a small surface area and thick waxy coats, both of which reduce water loss at a time when liquid water is not readily available.

In order to survive being eaten by animals, trees and shrubs employ a variety of strategies. Some produce nasty-tasting substances in bad-tasting glands (like Alaskan birches). Others smell bad (like false azalea and some currants, which actually smell like skunk spray). Some have coverings of hair on the young twigs or buds (willows and saskatoons), and others develop prickles or spines (devil’s club and prickly roses). A lot of these features are masked under summer foliage but, in winter, when the branches are ‘naked,’ we can observe these survival adaptations and use them to identify the plants.

Useful knowledge
Besides being fun and adding interest to your winter outings, knowing the plants in winter may be very useful. For example, if you are in pain out in the woods and have no pain-killers, it is good to know willow bark contains salicylic acid—the same compound as in aspirin. Buying property in winter? Knowing that devil’s club, alder and black twinberry indicate a wet site, or that cottonwood indicates underground water, could be very helpful. For sheer pleasure, looking with a magnifying glass at the amazing rusty scales of soapberry or the glistening crystalline glands of dwarf birch cannot be beaten. For environmental science students, whose school year corresponds with the period of botanical dormancy, learning to identify plants in winter is a must. The same is true for professionals like foresters, wildlife biologists and botanists, who make their living on the land.

Whatever your motivation, even small investments in understanding the natural history of our winter environment will be rewarding.