Trees benefit us in many ways. They can also cause major damage when limbs or the whole tree falls on power lines, cars, houses or people. Usually, weakened trees give some warning signs of danger. By learning to recognize the signs and to follow-up with prompt, proper action, you can often manage this risk, saving yourself grief as well as money.
What is a hazard tree?
A tree failure occurs when a tree or large part of a tree breaks and falls. Hazard Tree Management deals in probabilities of failure rather than certainties. Age, species (especially rooting and branching characteristics), site, and condition all influence the relative hazard of the tree. A high probability of failure does not make a tree a hazard; there also must be a target that could be damaged or injured if the tree fails.
Trees become a potential hazard when there is a target. A target is a structure, vehicle or a person that would be struck by a falling tree or its parts. A tree leaning over the bedroom is most hazardous. Trees near high use areas are more of a risk than those near infrequently visited areas, as the probability of a person being hit is greater. Priorities for removal or corrective treatments depend on the hazard rating of the tree.
What can you do?
Check your trees, especially large, old ones. Periodic, thorough inspections are essential to prevent accidents. At least one inspection per year should be made, but two per year are recommended, one in the summer while the leaves are on the tree and one in the winter. Every tree likely to have a problem should be inspected from bottom to top, looking for signs of root or butt rot and continuing up the trunk toward the crown, noting anything that might indicate a potential hazard.
A word about your liability. If you have a hazard tree, you may be responsible for any damage it causes if it falls. If a tree in your yard fails and damages your neighbor's property, and you have no prior knowledge of its condition as a hazard tree, your neighbor's general policy may cover the damages. This determination however, may be disputed. Documenting the condition of your trees can be important in case of litigation involving the failure of a tree.
Since all trees are potential hazards, the only way to completely eliminate a tree hazard is to remove the tree. Where this is not acceptable, regular inspection and appropriate action is the best way to “have your trees and reduce your risks.” Dead trees within the range of a target should be removed. A common question is “How long does it take a standing tree to fall after it dies?” The small twigs and branches typically fall first, followed by larger branches and ultimately the trunk. This process can take several years.
Pruning, cabling and bracing are remedies for reducing hazards and keeping a tree in the landscape. These generally require special tools, equipment and expertise, but certain trees are worth the investment. Prune dead, broken or hazardous branches correctly.
Weak branches or V-shaped forks can be supported with wire cabling or braced with metal rods. Appropriate treatments vary in cost and required expertise.
Prevention is the best action. Start a tree health program as soon as possible. Proper selection and placement of trees prevents many hazard problems. Hazards are often created when a tree is bought and planted, regardless of the original intention.
Care of trees during construction projects is also very important in avoiding tree hazards.
Ray Ridlen is an agriculture/horticulture educator for the Oklahoma County Extension Service. His column addresses frequently asked horticulture questions. For more information, call 713-1125.