Tree Risk Assessment

A giant oak tree dramatically ripped in half at its base

This tree had codominant stems instead of a strong central trunk, leaving it vulnerable to storm damage.

Making sure the trees surrounding your home are healthy is always important. Not only are unhealthy trees unattractive, they can be a serious safety hazard. The best way to determine if your trees are healthy is to contact an International Society of Arboriculture (ISA) Certified Arborist.

But you can do some scouting in your own landscape and determine if some of your trees are a risk and should be looked at by a professional.

It's important to remember that not all trees are a risk. It can be frightening to imagine tree damage, but trees play a vital role in your landscape. They not only provide you with cooling shade, trees play an ecologically important role. Trees remove carbon dioxide and pollutants from the air, and aid in the reduction of stormwater runoff.

What to look for

Dead branches/broken branches
Dead branches are usually easy to identify by their lack of bark and leaves. Remember that some trees are deciduous, so simply missing leaves does not mean a branch is dead. Be sure to look over your whole tree; it can be easy to miss branches that are high up in the canopy, but these branches have the potential to cause more damage since they would be falling from a greater height. Broken or hanging branches are an obvious safety hazard—it's only a matter of time before the branch falls.

Decaying wood is not always easily discovered on a tree, and even once discovered it can be difficult to tell how significant the problem is. The presence of conks (shelf fungus on a tree) or other fungal fruiting bodies, carpenter ants, and animal nesting holes can indicate decay damage to a tree.

A shelf-like mushroom growing on the side of a tree trunk

A "conk" growing on a tree trunk.

Cavities are another sign that might mean your tree is a risk. Cavities can be caused by decay and are usually places where the tree has been injured in the past. Be careful when trying to get a good look at any cavities in your tree, as wildlife and insects love to shelter in these cozy spaces.

Codominant Stems
Branches that originate from the same point on a tree are called codominant stems. These branches can be particularly vulnerable in strong storms or hurricanes, and the risk increases when branches are of similar size. Branches that make a sharp "V" are more vulnerable. Branches that form a wider, smooth "U" shape in the space between them are less risky. Corrective pruning or installing a cable system can help mitigate the risks, but these should be done with the help of an experienced arborist.

People fly around the world to see the Leaning Tower of Pisa, but a leaning tree may be a cause for concern. Trees can develop a lean for different reasons. A tree that starts to lean quickly needs immediate attention. A tree that begins to lean slowly over time is not as bad as a rapidly occurring lean, but should still be looked at by an ISA Certified Arborist.

Root problems
Root problems can be difficult to notice since they are often mostly hidden out of sight by soil and mulch. Most trees should have a well-defined root "flare" that you can see above ground. If the tree has been planted too deeply or soil has been added over this root flare, it can cause issues with your tree roots. And roots above the surface can potentially cause their own problems if they begin to grow tightly around the base of the tree. This is called "girdling" — see an example here.

Some other clues that you might have root issues are visible cavities or swelling in the root collar, fungal conks or mushrooms growing around the base of the tree, or visibly broken root stubs. If you suspect root problems, a certified arborist can be called in to determine if your tree is a risk.

What can I do?

You can look over the trees in your landscape yourself, but if you have any concerns it's best to call an ISA Certified Arborist. Determining if a tree is a risk to your home or those around you is a difficult process and it takes someone with training and experience to really know if a tree should be removed.

Trees play such an important role in our ecosystem that it's best to allow them to remain in your landscape if they are safe. An arborist with experience in tree risk assessment is your best bet to make sure your trees are safe and that you don't unnecessarily remove any. It's important to note that tree removal is not the only option; sometimes the damaged parts can be removed.

The bottom line: when in doubt, call an ISA Certified Arborist. You can also contact your county Extension office for help getting in touch with a certified arborist in your area.

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