When powerful storms move through the state, we get a lot of questions about damage to trees and what folks can do about it. I put together some information on how trees are affected by high winds and snow/ice loads, how they respond, and what you can do to try and get your trees back to an upright position.
A good starting point is to remember that trees deal with wind on a regular basis. They are used to being bent and twisted and can handle some high wind gusts, especially if they are surrounded by other mature trees. When heavy snow and ice loads mix with high winds is when we tend to see branch breaks and other damage.
I asked Scott Bowe, our resident wood expert in Extension, how trees are adapted to snow and ice loads and he said this: “… softwoods did evolve in colder climates and their shape is adapted to snow loads. The cone shape of spruces and firs helps shed snow, but this does not always work as seen in the woods when the cone is completely bent over from heavy snow load.”
Trees vary in their ability to handle a snow or ice load before breaking and/or returning to their original form. One strength measurement that engineers use is called the modulus of rupture (MOR) or bending strength, which provides insights into which trees will fare better in heavy winds, or snow and ice. MOR measures a particular species’ strength before the wood fibers break under a given load. Butternut, aspen and basswood are on the low end of the MOR spectrum and will break more easily than say hickory, birch and oak which are on the high end.
If you are nerding out on all of this and want to see where other species fall on this spectrum, you can read more on this website for MOR.
Now let’s talk about how your trees can be damaged from heavy winds and snow/ice load. Broken branches and treetops are obvious signs of injury, but there can be damage that might not become apparent for years, or until it is harvested and sawn into lumber. Some of the cells within the main trunk of the tree may have ruptured or you could get a separation of the annual growth rings within the trunk called ring shake. Some clues that your trees might have ring shake include a lean, a crook or sweep, large overgrown knots, and things like bulges and burls near the base of the tree. There can be other causes for these conditions as well, so it can be hard to make a definitive diagnosis.
Finally, here are some things you can do about all this. If your trees have a lot of obvious damage, then those would be good ones to harvest. You might end up having to remove more trees than you like, but at least you will still get some value out of those trees before they degrade. It is a good idea to bring in a forester for advice on which to harvest/salvage. You can find foresters that work in your county using this website: dnr.wi.gov/fal.
If you have smaller trees (e.g. saplings or small pole sized trees) that are bent over due to a heavy snow or ice load, do what you can to remove that load and restore your trees to their original position. The longer you leave them bent over, the harder it will be for them to straighten up. Some folks have used a pole pruner or other long tools to knock the snow/ice off and push the top of the trees back up.
Do what you can now to protect your trees and the health of your woodland, and the next time a storm comes through you can quickly act to help your trees.