Trees provide significant
benefits to our homes and cities, but when trees fall and injure people
or damage property, they are liabilities. Taking care of tree hazards
makes your property safer and prolongs the life of the tree.
Trees are an important part of our world. They offer a
wide range of benefits to the environment and provide tremendous beauty.
However, trees may be dangerous. Trees or parts of trees
may fall and cause injury to people or damage to property. We call trees
in such situations hazardous, to signify the risk involved with their
presence. While every tree has the potential to fall, only a small
number actually hit something or someone.
It is an owner’s responsibility to provide for the
safety of trees on his or her property. This brochure provides some tips
for identifying the common defects associated with tree hazards.
However, evaluating the seriousness of these defects is best done by a
professional arborist. Regular tree care will help identify hazardous
trees and the risk they present. Once the hazard is recognized, steps
may be taken to reduce the likelihood of the tree falling and injuring
Hazardous Trees and Utility Lines
Trees that fall into utility lines have additional
serious consequences. Not only can they injure people or property near
the line, but hitting a line may cause power outages, surges, fires, and
other damage. Downed lines still conducting electricity are especially
dangerous. A tree with a potential to fall into a utility line is a very
Tree Hazard Checklist
Consider these questions:
- Are there large dead branches in the tree?
- Are there detached branches hanging in the tree?
- Does the tree have cavities or rotten wood along the trunk or in
- Are mushrooms present at the base of the tree?
- Are there cracks or splits in the trunk or where branches are
- Have any branches fallen from the tree?
- Have adjacent trees fallen over or died?
- Has the trunk developed a strong lean?
- Do many of the major branches arise from one point on the trunk?
- Have the roots been broken off, injured, or damaged by lowering
the soil level, installing pavement, repairing sidewalks, or digging
- Has the site recently been changed by construction, raising the
soil level, or installing lawns?
- Have the leaves prematurely developed an unusual color or size?
- Have trees in adjacent wooded areas been removed?
- Has the tree been topped or otherwise heavily pruned?
Defects in Urban Trees
The following are defects or signs of possible defects in urban trees
- regrowth from topping, line clearance, or other pruning
- electrical line adjacent to tree
- broken or partially attached branch
- open cavity in trunk or branch
- dead or dying branches
- branches arising from a single point on the trunk
- decay and rot present in old wounds
- recent change in grade or soil level, or other construction
Defects in Rural Trees
The following are defects or signs of possible defects in rural trees
- recent site construction, grading and tree removal, clearing of
forests for development
- previous tree failures in the local area
- tree leaning near a target
- forked trunk; branches and stems equal in size
- wet areas with shallow soil
Managing Tree Hazards
An arborist can help you manage the trees on your
property and can provide treatments that may help make your tree safer,
reducing the risk associated with hazardous trees. An arborist familiar
with hazard tree evaluation may suggest one or more of the following:
- Remove the target. While a home or a nearby power line
cannot be moved, it is possible to move picnic tables, cars, landscape
features, or other possible targets to prevent them from being hit by
a falling tree.
- Prune the tree. Remove the defective branches of the tree.
Because inappropriate pruning may weaken a tree, pruning work is best
done by an ISA Certified Arborist.
- Cable and brace the tree. Provide physical support for weak
branches and stems to increase their strength and stability.
- Provide routine care. Mature trees need routine care in the
form of water, fertilizer (in some cases), mulch, and pruning as
dictated by the season and their structure.
- Remove the tree. Some hazardous trees are best removed. If
possible, plant a new tree in an appropriate place as a replacement.
Recognizing and reducing tree hazards not only increases
the safety of your property and that of your neighbors but also improve
the tree’s health and may increase its longevity!
Ensuring Quality Care for Your Tree
Trees are assets to your home and community and deserve
the best possible care. If you answered “yes” to any of the questions in
the tree hazard checklist or see any of the defects contained in the
illustrations, your tree should be examined.
International Society of Arboriculture