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Historic weather events are memorable, and very few trees, no matter how great of condition they are in, can withstand the force of hurricane winds. Despite such major events, trees failing in strong thunderstorms are much more common -- and the vast majority of these had some predisposing factor that led to the failure. A good rule to pass along to tree owners is, “Storms do not cause tree problems, they reveal them.” While not every case of tree failure is 100 percent predictable, there are many ways to determine if failure is a possibility. Let’s take a look at some of the most common types of storm-related tree failures and which warning signs we can be on the lookout for.

Storm Damage and Trees

By Brandon Gallagher Watson


On a Friday night in late June last year, I sat by my front window watching a tremendous thunderstorm with my children. Trash cans were blowing up the street, the lights were flickering, and then we heard the unmistakable “CRRRACK” of a neighbor’s tree snapping and crashing down. Shortly after, our power went out and remained off for five days. My kids’ first thought was, “Is our house going to be okay?” My first thought was, “Whoa, we are going to be busy!” And busy we were. Our office received more than 3,000 phone calls that weekend from longtime customers, as well as people who had never thought to call a tree service before in their lives. Some of our crew members worked more than 60 hours that first week just getting the most dangerous stuff off of people’s roofs. We booked work from the June storm well into February of the following year.


Every person working in the tree business has a storm story — “The Blow-Down in ’87,” “The Fourth of July Tornado,” “The November Ice Storm,” etc. Each of these events has its own character, creating unique experiences and challenges for the men and women on the front lines of the cleanup effort. One thing is certain with each one though, they create a ton of work for tree care professionals. We see so much destruction after storms that’s it’s easy to say “Storms are bad for trees. Period.” What homeowners, and even we as professionals, often don’t often stop and ask is, “Why did that tree suffer storm damage and that one did not?”


Storms cause damage to trees. Major weather incidents such as Hurricane Katrina, Hurricane Sandy, or the 2013 Ice Storm that ran from Texas to Toronto certainly stick out as catastrophic events. The damage caused to homes, infrastructure and power lines from trees in the 2011 Halloween Nor’easter alone was estimated to cost between $1 billion and $3 billion, leaving some residents without power for up to two weeks.


Historic weather events such as these are memorable, and very few trees, no matter how great of condition they are in, can withstand the force of hurricane winds. Despite these major events, trees failing in strong thunderstorms are much more common — and the vast majority of these had some predisposing factor that led to the failure. A good rule to pass along to tree owners is, “Storms do not cause tree problems, they reveal them.” While not every case of tree failure is 100 percent predictable, there are many ways to determine if failure is a possibility. Let’s take a look at some of the most common types of storm-related tree failures and which warning signs we can be on the lookout for.


 


Whole tree failure


Whole tree failure, or complete tree failure, is when the tree — trunk, limbs, leaves and all — comes down. Most of these cases are the result of some issue with the root system. Conifers, such as spruce and fir, are frequent victims of this, as their dense foliage becomes a sail in high winds. Couple this with any number of site issues such as confined root areas, poor soil, or waterlogged soil, and the failure risk goes up. Trees that have had any type of site alterations in the past 10 years, such as grade changes, new construction, or trees that used to be a group that are now solo trees can be more vulnerable to strong weather elements such as wind.


Trees failing at the soil line can also be predisposed by other root issues, such as root severing, and stem girdling roots (SGR). SGR occur at or just below the soil line when an encircling root grows partially or completely around the trunk. As the root increases in girth, it essentially chokes off the roots on the affected side. This creates a weak point that is often the point of failure — no different than in trees with severed roots.


 


Whole tree failure — predisposing factors:

Trees with significant lean
Lean that has noticeably increased in recent years
Root plate lifting
Waterlogged soils
Mushroom around base or trunk of the tree
Recent root severing
Recent (within ten years) site alterations
Trees planted too deep
Trees with flat sections at base where root flares should be

 


Canopy failures


Much more common than whole tree failure are canopy failures where large branches and limbs break off during a storm event. There are several different things that can predispose canopies to fail. One is simply the type of tree as some species are much more likely to fall apart in high winds than others. Every region of the country will have its most common trees known to be branch-fail hazards. Species such as poplar, willow, callery pear, box elder, ash, white pine, hackberry and Norway maple all jump to mind as the most likely to drop a limb, but every tree species is certainly capable.


A tree’s form is the next most common factor for limb and branch failure. Often, homeowners plant a small tree from the nursery and never preform any structural pruning after that. This can result in trees with the ‘candelabra’ shape with many heavy, large branches originating low on the trunk. Trees with co-dominate or multiple leaders are often unable to withstand the forces of high winds, snow and ice. Where the co-dominate leaders meet can typically be included bark. This occurs at poor unions and becomes an origin point for decay.


Decay is another contributing factor to limb and branch failure. Any wound in the bark, whether created by insects, birds, people, or other mammals can be an opening for fungal organisms to begin consuming — and thus weakening — the wood. Decay can occur anywhere from the roots to the base, the trunk, and up through the canopy. When inspecting a tree, ensure it has been observed from all possible angles as even serious structural decay is not always apparent at first glance.


When explaining decay risks with tree owners, discussing the difference between “health” and “condition” can be a useful distinction. “Health” refers to the vitality of the tree while “condition” is used when discussing the tree’s structural integrity. A tree may appear to the homeowner as in “good health” because it has green leaves and pretty flowers this year, but it may be in significantly “poor condition” and present a hazard to the site. Educating tree owners on poor structure, decay, and the risks that come along with them may help keep their families and properties safe from a possible tragedy.


 


Canopy failure — predisposing factors:

Tree species well known for limb and branch failures
Poor structural forms
Co-dominate leaders
Included bark
Decay in trunk or major limbs
Woodpecker damage

 


Storms can reveal tree problems, but it is important to remember that failures can still happen on clear days as well. Last summer, a woman in Eden Prairie, Minn. was killed while jogging when a decayed white oak failed in a park on a sunny day.


Regular inspections of the tree by a trained arborist are the best prescription for minimizing risk. While even the professionals will not catch every predisposing factor or be able to prevent damage from failures all the time, there is no better way to educate tree owners on the red-flags of hazards we as arborists see.


A tree can simultaneously be the most valuable and most dangerous thing in a homeowner’s yard. It is easy to look at a tree after it failed and say, “Yep, here is exactly why it fell on your house, ma’am,” but it is often difficult to see those risk factors prior to failure, and often it is even harder to get tree owners to take preemptive action. Two things are certain: storms will occur and trees will fail in those storms. We can take a roll in not just the cleanup effort, but in the prevention effort as well.


 


Brandon Gallagher Watson is director of communications at Rainbow Treecare Scientific Advancements, and is an ISA Certified Arborist (#MN-4086A).


 

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