Trees are essential to our world, offering a wide range of benefits to our environment. However, trees become hazardous liabilities if they fall and injure people or damage property.
As you get to know the ins and outs of your new property, take some time to carefully inspect any trees growing there. With the help of this checklist, you'll be able to identify any potential safety issues before they become a serious hazard.
What to Look For
There are seven important signs that indicate when a tree is failing:
- dead wood,
- weak branch unions,
- root problems, and
- poor tree form.
Just because a tree has one or more of these defects does not mean that it's hazardous. A tree is only considered to be a hazard if some portion of it is within striking distance of a target, such as homes, roads, or passersby.
#1 – Dead Wood
Dead trees and branches are unpredictable and can break and fall at any time. Dead wood is often dry and brittle and cannot bend in the wind like a living tree or branch. A dead branch that is already broken off (a “hanger” or “widow maker”) is especially dangerous.
- A broken branch lodged in a tree.
- A dead tree.
- A dead branch that's large enough to cause injury if it falls. Typically, this is a branch larger than 4 inches in diameter, but this can vary with branch height. Even smaller branches, falling from high in the tree, can cause serious personal injury.
#2 – Cracks
A crack is a deep split that goes through the bark and into the wood of the tree. Cracks are extremely dangerous because they indicate that the tree is already failing.
- A crack that extends deeply into, or completely through the stem.
- Two or more cracks in the same general area of the stem.
- A crack that's in contact with another defect.
- A branch of sufficient size to cause injury if cracked (typically larger than 4 inches in diameter).
#3 – Weak Branch Unions
Weak branch unions are places where branches are not strongly attached to the tree. A weak union occurs when two or more branches grow so closely together that bark grows between the branches and inside the union. This ingrown bark, called “Included bark,” does not have the structural strength of wood and can make the union very weak. The inside bark may also act as a wedge and force the branch union to split apart. Trees with a tendency to form upright branches, such as elm and maple, often produce weak branch unions.
- A weak branch union on the main tree trunk.
- A weak branch union that's associated with a crack, cavity, or another defect.
#4 – Decay
Decaying trees are prone to failure, but the presence of decay alone does not necessarily mean failure. Still, advanced decay (soft, crumbly wood with a cavity) is serious. Evidence of fungal activity, such as mushrooms and conks, are indicators of advanced decay. Decay is very common on the majority of large maple trees we have in Northern Virginia because of their large size and structure.
A tree usually decays from the inside out, forming a cavity, but sound wood is added to the outside of the tree as it grows. Trees with sound outer wood shells are relatively safe. Still, evaluating the safety of a decaying tree is usually best left to trained arborists.
- Advanced decay associated with cracks, weak branch unions, or other defects.
- A large branch that's decayed.
- A tree with interior decay where the thickness of sound wood is less than 1 inch for every 6 inches of diameter, at any point on the stem.
#5 – Canker
A canker is a localized area on a stem or branch of a tree where the bark is sunken or missing. Cankers are caused by wounding or disease. The presence of a large canker increases the chance of the stem or branch breaking near the canker.
- A canker that affects more than half of the tree’s circumference.
- A canker that is physically connected to a crack, weak branch union, or cavity.
#6 – Roots
Trees with root problems may blow over in windstorms or even fall from the weight of the tree’s leaves in summer. Root problems can be caused by severing or paving over roots, raising or lowering the soil depth over roots (such as from a landscaping project), traffic over the roots, or root decay. Dieback, dead wood in the crown, and off-color or smaller than normal leaves are symptoms associated with root problems. These above-ground symptoms may serve as your best warning.
- A leaning tree with recent root exposure, soil movement, or soil mounding near the base of the tree.
- A tree that has had more than half of the roots under the tree’s crown cut or crushed.
- Advanced decay visible at the base of the tree or on the buttress roots.
#7 – Poor Tree Form
Trees with strange shapes are interesting to look at but may be structurally defective. Poor tree form often results from many years of damage from storms, unusual growing conditions, improper pruning, topping, and other damage.
- A tree that's leaning excessively.
- A large branch that is out of proportion with the rest of the crown.
A high-risk situation increases as the number of tree defects increase!
Finding multiple defects in a tree should be your red flag when evaluating its potential to fail. Multiple defects that are touching or are close to one another should be carefully examined by a Certified Arborist. If more than one serious defect occurs on the tree’s main stem, you should assume that the tree poses a very high level of risk and corrective actions should be taken.
What to Do
If a high-risk situation exists, there are four recommended options for correcting the problem:
- move the target
- prune the tree or install cables
- convert the tree into a wildlife tree
- remove the tree
Move the Target
Moving the target is often an inexpensive, effective, and simple way to deal with a high-risk tree. Easily moved items like play sets and swings, vehicles, and picnic tables can be placed out of the reach of the hazardous tree with little effort and expense. If the target cannot be moved and a high-risk situation exists, consider blocking access to the target area until the hazard can be eliminated.
Prune the Tree
A defective branch or branches may cause a high-risk situation, even though the rest of the tree is sound. In this case, pruning the branch or branches solves the problem.
Practicing proper tree pruning is excellent “preventive medicine” for reducing the occurrence of defective, high-risk trees. By pruning properly, early in a tree’s life, you can prevent or correct many of the problems that cause trees to fail as they mature. Improper pruning techniques can worsen the problem, and may ultimately result in the formation of cracks, decay, cankers, or poor tree architecture that lead to very high-risk situations.
Create Wildlife Habitat
This option is often overlooked but is an excellent way to help support local wildlife. Instead of removing the entire tree, preserve a part of it to provide wildlife habitat. One option is to reduce the height of a tree to the point that it would no longer strike a target if it should fail. Remove major branches that are defective, and leave a portion of the tree intact for wildlife habitat. If a tree must be removed for safety reasons, consider leaving the tree on the ground to create wildlife habitat.
Remove the Tree
We look at tree removal as the final option to be used only when the other corrective actions will not work. Tree removal is inherently dangerous and is even more serious when homes and other targets are involved. Removal of very high-risk trees is definitely a job for a professional.
One More Option: Cabling and Bracing
Cabling and bracing do not eliminate all the safety risks associated with a highly defective tree. But, when done correctly by a trained arborist, it can extend the time a tree or its parts are safe. Done incorrectly, it creates a more serious hazard. Cabling or bracing is not recommended for a high-risk tree unless the tree has significant historic or landscape value, the cabling or bracing is done by a trained professional, is regularly inspected, and properly maintained.
Evaluating and treating tree hazards can be a complicated process, requiring a certain level of knowledge and expertise. Proper maintenance will help prevent dangerous trees, while this checklist will help you identify when a tree does become dangerous.
A professional should be consulted when undertaking many of the suggested corrective actions. When in doubt about how much risk a defective tree poses, or how to best treat it, give the professionals at Riverbend Tree Service a call.
Remember that trees do not live forever. Design and follow a backyard landscape plan that includes proper tree selection and a cycle of tree maintenance and replacement. This is the best way to preserve the health of your trees and ensure a safe and enjoyable outdoor experience.
Want a more in-depth inspection?
Call us today at 703-402-9366 or click the button to contact us for a free inspection. Our arborist will let you know if there are any issues that should be corrected and, if so, will provide a professional, no-obligation estimate for the recommended work.