What makes some trees more likely to fail during a storm?  It’s not always easy to predict which trees will fall victim, but there are factors that can increase risk.  Take a close look at your trees to see how many of the following risk factors are present:

1.     Limited root zone or damaged roots:  Large trees with limited space for root zones are especially prone to wind throw.  Roots that have been structurally compromised from construction, disease, compaction and other factors fall (no pun intended) into the same category.  Ground saturation from excessive rainfall or irrigation can cause roots to release their grip from the soggy soil and uproot, especially if high winds come into play.

2.     Thick, heavy canopies:  Thick canopies may catch the wind like a sail.  This can put tremendous pressure on weak attachment points and the root system, often leading to structural failure.  This is also why live trees seem to create more storm damage than dead trees, although in a storm, any tree can fail.  Some species are particularly susceptible to wind damage.  They include Bradford pears, maples, and white pines, among others.

3.     Weak attachment points:  Strong attachments points where the branch meet the trunk are shaped like a “U”.  Weak attachment points are shaped like a “V”.  As the branch and trunk each grow in diameter, they eventually start to push against each other.  Additionally, as the tree grows, bark becomes included within that union, further weakening it.  Tree species known for this defect are Bradford pears, lindens and maples in general.

4.     Co-dominant leads:  Structurally sound trees have one dominant trunk.  Trees with two or more dominant leads suffer storm damage as the trunks blow away and towards each other at varying rates with the wind.  Furthermore, they frequently have included bark at the union.

5.     Structural damage:  Pre-existing structural damage such as vertical cracks, cavities, broken branches, girdling roots, etc., can cause tree failure.

              The risk factors mentioned above, individually and collectively, can result in a tree’s failure during a storm.  However, as the following quote from an article published by the Tree Care Industry Association entitled “Deaths from Wind-Related Tree Failures”By Thomas W. Schmidlin, Ph.D., even structurally sound trees can fail if the storm is severe enough.

               “For hardwood trees, such as oak, maple, birch and ash, a three-second gust of 74 mph will break large (greater than 1 inch) branches, 91 mph will uproot trees, and 110 mph will snap tree trunks. For softwood trees such as pine, spruce, fir and hemlock, a three-second gust of 75 mph will break large branches, 87 mph will uproot trees, and 104 mph will snap tree trunks. These are not absolute numbers but a value near the middle of the range of minimum wind speeds expected to cause the damage. 
               Wind speeds of these magnitudes occur with weak tropical cyclones, weak tornadoes, thunderstorm downbursts and winds associated with mid-latitude cyclones, among other meteorological events. In addition, heavy accumulations of snow or ice may cause trees to fail even with lighter wind speeds.”