If I was to ask you for some winter words, you might come up with toque, toboggan, snowshoe, ski, or “stressful driving conditions.” However, I’m fairly confident the following two words would not be top of your list: marcescence or subnivean. Am I right, or what?
OK, like you, probably neither are in my top 100 words of winter, but we all should be aware of what they mean and what phenomenon nature is undergoing.
Whilst you were out and about doing some early winter walks, did you notice that many oak and beech trees still have their leaves attached? What’s up with that? Maples and ash are barren of leaves, but scattered throughout the woodlot are many bronze coloured hardwoods, although mainly just at the lower levels of the tree.
This is called marcescence (pronounced mark-a-sense, unless you are a Latin teacher and in that case you may have a differing opinion on the pronunciation; keep your cards and letters coming). Back to the trees.
Normally, in hardwood trees, in the autumn, there is a thin corky layer that grows between the existing leaf petiole and the newly forming bud. This is called the abscission layer and it shuts off the sap flow between the leaf and the branch.
Leaves are not needed in the winter, and they are a liability to freezing if water remains in the thin green cells. Cut ‘em loose, get rid of them!
As the abscission layer thickens, the leaf is no longer securely anchored to the branch and a moderate wind gust will tear it away to drop it on your recently raked lawn. A good November wind storm is usually the efficient way that a tree is denuded of these useless leaves.
And what about the beech and oak, you ask, why do they still have their, albeit dead, leaves attached? Good question. However, the answer is still eluding forest researchers.
But, being good researchers, they have a concept of an answer.
One option is that the dead leaves are protecting the new buds from deer browsing. Deer like to nibble on the tips of maple and hemlock to get nutritious food, but a mouthful of dry crumbly leaves usually gets a pass. This goes along with the observation that most of the retained leaves are on the lower branches or younger trees, both of which are within reach of a hungry deer.
The other explanation that is being floated about, is that the dead leaves physically assist the new buds by acting as solar collectors to retain heat on the branch. And to deflect snow and ice from building up on the tender leaf bud.
Both explanations of marcescence make sense, kind of. I leave it with you for further research.
Now, about that other winter word, subnivean. Sub means below, and anything nivean is related to snow. If you have already had your morning coffee, you have no doubt figured out that subnivean refers to all that goes on under the snow. Hey, extra sugar for you!
There is indeed a zone between the surface of the ground and the bottom of the snowpack, and a lot goes on there all winter long. This thin layer is caused by the tiny insulating air pockets trapped between the fallen snowflakes, and the geothermal release of heat from the ground. Not a sauna, but warm enough to melt a thin zone.
This is where the non-hibernating mice, voles and shrews frolic the winter months away. As the little critters run to and fro along their winter wonderland of tunnels, they release a bit of heat of their own, which melts a bit of the overhead snow to refreeze like a snow tunnel. Cozy!
Apparently it takes about eight inches of snow (OK, ya, 20 centimetres, happy now?) to form a solid roof. When the snow melts in springtime these tunnels are easily seen as they melt later than the surrounding snow.
This warm(ish) layer is also home to beetles, grubs, plant seeds, and fallen berries. Like a refrigerator, things are kept cool but not frozen solid, thus allowing for an early spring release.
The other creature that likes deep and fluffy snow is the ruffed grouse. These birds practise a subnivean ritual when the nights are cold and the snow is deep. They will rocket themselves into the deep snow and then tunnel a few inches away from the entrance hole. The insulating combo of loose snowflakes and layers of feathers allows the grouse to survive a night of really cold air.
Sound is transmitted sideways through the snow and, even if a bit muffled, the grouse can hear the sounds of a snuffling coyote or wandering photographer on snowshoes.
The bird waits until the last possible second before exploding upwards, sending snow flying in all directions and causing the coyote or fox to jump back in surprise, or the wandering photographer to wish he had stopped for a bathroom break prior to heading out.
Owls and foxes have incredible hearing abilities, and even when that meadow vole is crawling along its secure little tunnel, these predators can hear a leaf crumple here, a twig rustle there, and triangulate depth and location of lunch. They are amazingly good at it, much to the displeasure of the voles.
Looking out the window I sense more winter words ... snow, shovel, snow shovel, snow again, shovel again ... snow blower!
