Published in the York Weekly, Portsmouth Herald, Foster’s Daily (and more) Dec 14 2020
I went up to Blue Job Mountain State Park for a walk last weekend. There was a lot more snow up there than where I live in North Berwick. Lining the parking lot were the birch trees, bent over, touching the ground, with their heavy loads of icy snow. Hiking up to the summit of Little Blue Job was an obstacle course as we worked our way around all different types of trees, some were flexible like the birch and bent by the snow, some had snapped.
And they seem not to break; though once they are bowed.
This got me thinking about birches. They are known for bending and not breaking. Most of us read Robert Frost’s poem about boys swinging on birches in high school, but there is a part about the birches themselves “Shattering and avalanching on the snow crust—Such heaps of broken glass to sweep away. You’d think the inner dome of heaven had fallen. They are dragged to the withered bracken by the load, And they seem not to break; though once they are bowed.” where Frost talks about how birches bend and aren’t broken by the snow. He talks about how sometimes they stay bowed after a long winter “So low for long, they never right themselves: You may see their trunks arching in the woods. Years afterwards, trailing their leaves on the ground.” The sad thing was, people had made it worse by walking over their heads, cementing them into the icy trails. Many were snapped by the weight of feet and all it would have taken was that first person on the trail to free the birches from their icy load, pull them out of the snow and let them spring back up towards the light.
Adaptations to the North
This ability of birches to bend is an adaptation to living in the north. We have a number of different species of birch in New England, among them, paper birch (Betula papyrifera), is one of our most widely-distributed trees, found from Newfoundland west to British Columbia and south to New York and South Dakota. It is also one of a handful of broad-leaved trees that can live in the far north. It can live so far to the north because of those flexible branches. Its northern neighbors, balsam fir and hemlocks, have a different adaptation to the same conditions and are cone-shaped; their long sloping branches help snow slide off instead of collecting on the branches and causing them to snap.
Flexibility isn’t a paper birches’ only adaptation to northern climates. During cold winters the thick, dark bark of an oak or ash becomes a liability, absorbing sunlight during the day and heating up, only to cool down again, usually quite rapidly, at night. This heating and cooling can kill the cells of the cambium, the layer of cells between the bark and the wood that is responsible for the growth of the trunk. Rapid temperature fluctuations can also severely injure a tree by causing frost cracks to form in the bark.
In contrast, the highly reflective, light-colored bark of a paper birch doesn’t absorb the sun’s radiation and heat on cold winter days, and so avoids the damage caused by rapid heating and cooling.
What causes this extreme whiteness? That white powder that coats the bark is primarily composed of a chemical called betulin. The cells in the outer layers of bark contain betulin crystals that are arranged in such a way as to reflect light and appear white.
Free the Trees!!
My walking partner is a tree enthusiast. She felt sorry for all those forlorn birches bending under their heavy loads, and even more sorry for the birch tops that had been cemented into the trails by uncaring feet, or even worse, those that had snapped due to this trammeling. She started clearing as many as she could. Pulling the tops out of the snow and letting the trees spring free. It was exhilarating and infectious to watch. I joined in and we spent more of our time freeing birches than walking. I don’t know whether this really will help the trees survive the winter, but figure it can’t hurt. I’ve read that Frost once said “it was almost sacrilegious climbing a birch tree till it bent, till it gave and swooped to the ground, but that’s what boys did in those days”. I agree, it is sacrilegious, and feel like now we should know better. Trees have a hard enough time these days, if you see one struggling with the snow, why not help it out?