As promised in my last blog post Should I be worried about my tree blowing over in the wind, today were going to talk about tree failure/breakage due to wind. Unfortunately this is a much more likely thing to happen than your tree blowing over, and often times is a much more hazardous thing as well. When the tree can not take the forces generated by the wind it can fail in many places, and is very hard to predict where those places will be.
That being said, one place that you can look for signs of failure is at branch unions or what is commonly refereed to as a crotch. A strong crotch is usually “U” shaped, and in exclusive meaning the bark in the middle of it is pushed upwards and looks like a stegosaurus spine. This is in contrast to a weak crotch that is usually “V” shaped and in inclusive, meaning the bark goes inward making a very small groove.
The next thing that you can look for is if your tree is in proper shape or if it needs to be pruned. When there are branches that hang way outside the main shape of the tree they are more likely to get caught by the wind and break off, so they may be candidates for removal. Next, if the tree has lots of dead wood, that needs to be removed as dead wood is more likely to break out than live wood, and dead wood also can decay creating a weak are in the tree that can fail in the wind.
Contrary to popular belief, one thing you don’t want to do is heavily thin (not to be confused with crown clean) your trees thinking that it will allow the wind to pass through them better. Trees rely on interior branches for support, so that the tree may move as a whole instead of individual branches getting blown around. When a tree is heavily thinned a process called harmonic resonance is much more likely to take place.
Harmonic resonance occurs when the wind blows on a branch then backs off allowing the branch to spring back, then blows on it again, and the whole process repeats. It is like a kid on a sing, each time you push, the kid goes out, and comes back a little further than they did the time before, without you pushing them any harder. On the sing, eventually the kid will jump out and off, however in a tree this will take place until either the wind stops or the tree branch fails.
However outside of conifers trees that grow in the open will reach horizontally until they fail under their own weight, as well as being more susceptible to wind damage. A crown reduction that redistributes the crown from outside to the inside, and closer to the tree’s center of gravity can produce better aerodynamic symmetry, thus increasing the trees resistance to extreme winds and snow loads.
When the weather hits and the winds begin to blow, keep an eye on trees and be sure to contact your local certified arborist if you are at all concerned about your trees integrity.