Identifying hazard trees
Minnetonka Mike, the city of Minnetonka’s online request system, is always standing by to help you with any questions, comments or concerns you may have about your city. This month, Mike addresses a resident’s question about hazard trees.
Dear Minnetonka Mike:
Now that the leaves are gone, I notice some large holes in my tree where old pruning cuts were made. I watch woodpeckers near the holes, and there is always sawdust on the ground at the base of the tree. Should I fill the holes with something or should I remove it? The tree looked healthy this summer, but now I worry it may be sick or even dangerous. What should I do?
Signed, Tree Watcher
Dear Tree Watcher:
You have some great questions! I’ve prepared some information that I think will help you identify what’s happening with your tree. Read on to learn more.
Wood decay
A hole in a large branch or tree trunk is associated with wood decay. Decay starts soon after a tree is wounded, allowing an entry point for fungal pathogens. As the wood rots, it breaks down and can eventually form a hole where healthy wood once existed. The woodpeckers are attracted to the decaying wood because it provides a food source of beetles, ants, and centipedes.
Tree defense
Similar to a human’s immune system, trees have a defense system called compartmentalization that seals off as much decay as possible in the tree. Keeping a tree in good health helps a tree’s defense system, but there are instances when the amount of decay in a tree may make it unstable. Tree experts do not recommend filling a hole because it does not help the tree compartmentalize and may actually harm the tree.
Tree health vs. tree condition
If your tree is healthy, it may have a vigorous growth rate, large green leaves, and be free of pests. The health of a tree is different from its condition, though, which has more to do with the structure and stability of the tree. It sounds like the condition of your tree is compromised if there are holes in the tree—but it may also be healthy.
Do I have a “hazard” tree?
The next step is to determine if the tree is a danger to you or to a neighbor. The U.S. Forest Services says that a tree is a hazard if there are structural defects in the roots, stem, and branches that may cause the tree or tree part to fail, where such failure may cause property damage or personal injury. Said simply, a tree with structural problems is only a hazard if it has the potential to strike a “target.”
What else should I look for?
Survey the trees directly around your home, shed, patio or other areas where you spend time each winter. Keep in mind your tree may not present a hazard to your property, but may pose a risk for your neighbor. Remember, there must be structural defects plus a target to make it a hazard. A dead tree with bark falling off presents a fairly obvious risk if it is in close proximity to a structure. The wood will be brittle as it dries and can become soft as the wood decays.
Walk around each tree and look for holes (cavities) in large branches and the trunk; cracks in the stem, or between branches; and/or leaning or soil mounding at the base of the tree.
What should I do if I think I have a hazard tree?
When you find one or more defects on a tree, seek a consultation with a certified arborist in order to determine the level of risk the tree poses to failing, or hitting a target. Many factors contribute to a trees’ risk, including the species, age, and site on which it is growing. It is important to consult an expert because, in certain instances, your risk can be lowered and the tree saved by taking a few steps.
Is a dead tree always a hazard tree?
A standing dead tree, or “snag,” is not a hazard unless it has a chance of falling apart onto a target. Keep standing dead trees in wooded parcels for wildlife food, cover, and nesting. As the tree rots, it will become incorporated into the soil and add nutrients for other trees and plants to use. An exception to this rule is if the bark is still intact on a tree identified by the city as having Dutch elm disease or oak wilt.
What should I do if the hazard tree is my neighbor’s?
Be neighborly. Talk to your neighbor and explain what you can see from your property. Their sightline view may not be the same, or it might be in a part of their yard they do not use frequently. Ask your neighbor to mitigate the risk the tree poses to your property. Take a photo of the tree and write your observations in a letter to your neighbor, and keep a copy for yourself. Consider having a certified arborist look at the tree to evaluate the risk. If a conflict arises, consider using a mediation service to work through the conflict with your neighbor.
To learn more about trees and the law, read about Minnesota Trees and the Law online, in the 2004 MN Shade Tree Advocate article “Boundary Trees and the Law“ or the 2002 Bench & Bar’s “In the Shade of a Tree: Analyzing the Tree Related Legal Problem.”
What is the city’s role with hazard trees?
The city removes hazard trees from city properties, but does not require residents to remove hazard trees from private property. If there is a conflict with a hazard tree along a property line, it is considered a civil issue to be resolved between residents.
Dead elms with intact bark and red oaks with oak wilt are the only two types of trees that the city may require a property owner to remove. Learn more about the diseases regulated by the city by visiting the shade tree disease control program page.
If you have a question about your own tree, the city forester can suggest resources to determine if you should take action on your property.
Learn more about hazard trees.
If you have a question, comment or concern about the city, let Minnetonka Mike know! Just visit the Minnetonka Mike Online Service Request System page. Follow the directions to set up your account, then go ahead and submit your comment.
