Wild Side: Heavy snow is tough on trees
--By Dan Wilcox
We’ve had five storms in the last year that started out with sleet and freezing rain and then turned to heavy wet snow that loaded up on the trees. Several storms with four to six inches of wet snow occurred last April after the first bluebirds returned. On May 1 last year it was 50 degrees in the morning and by the next day we had over a foot of wet snow. Last week’s storm started with rain and left about a foot of snow at our place. If you are feeling a bit of winter fatigue, think of the trees.
Natural selection has resulted in a variety of branching designs in trees that are adapted to the climates where they grow. Tree branches must bear the loads imposed by the weight of leaves, water, wind, snow and ice. Wood is a remarkably tough and resilient material but it does have its limits. A cubic foot of wet snow can weigh more than 20 pounds. A cubic foot of ice weighs about 57 pounds. Many trees in our woods have been bent over or broken by the heavy ice and snow.
A simple way to understand the strength of wood is to think of a bundle of drinking straws that have been glued together. The straws represent the tubular cellulose fibers bonded together by lignin. The bundle is stronger in tension than in compression and is able to withstand many cycles of loading before breaking. Tensile strength of most wood is quite high and compressive strength is lower. When overloaded, the wood fibers buckle and crush, with cells deforming up to 20 percent before breaking.
Spruces, hemlocks, balsam fir, and white pine are species adapted to northern climates with drooping branches that shed snow. Being evergreens, they collect snow on their branches and create a sheltered space beneath them where many species of wildlife find shelter.
There was a lot of snow during my first winter in Wisconsin in 1970. Some friends and I went north to a cabin near Mellen in Ashland County. We snowshoed in to the cabin where the snow was up near the eaves and we dug our way down to get in the door. Skiing near the headwaters of the Chippewa River was beautiful until I skied too close to a spruce tree. What appeared to be a small tree was really a larger white spruce holding up a lot of snow. I fell into a “snow well” in a tangle of skis, poles, arms, legs and branches. It was quite a struggle to swim out of that situation.
Trees more adapted to southern climates and fast-growing trees are more susceptible to ice and snow damage. Box elders and black willows are fast-growing weedy trees that break easily under snow loads. The heavy snow last May created a jackstraw jungle of broken box elders along the rivers around here. Some of the tall, thin black ash and hickory trees along our road are bowed over by the snow and probably won’t recover.
It doesn’t really help to knock the snow off the trees in your yard. The wood is under tension and further movement can break branches. It’s best to wait for the snow to melt, assess damage, prune out broken parts and re-plant if needed. Like the squished mugo pine at the corner of our house, we are suffering a bit of winter fatigue and looking forward to spring.
Please send any comments and suggestions for this column to me at firstname.lastname@example.org.
--Dan Wilcox, outdoor columnist