IDENTIFYING HAZARD TREES

By Dick Ratcliff, ISA Certified Arborist, Outdoor Design Group

With wind storms this year and heavy snow last winter many trees have caused property damage, power disruption and even death due to failure. Most think this is an act of God. However, due to many improper cultural practices, carelessness and neglect many failures are not so surprising. There are signs that can indicate that trees have structural problems. Properly identifying these signs and taking steps to mitigate the problem can save money, prevent disruption in our lives, property damage, eliminate potential injury and prevent law suits.

The first step in identifying hazard trees is to understand the cause of most defects which are the result of injury or stress to the tree. Most injuries in our urban forest result from people and their activities. Such injuries include damage from weed eaters, lawn mowers, excavation within the root zone, damage to the trunk whether mechanical or vandalism and breaking of limbs. Stresses include too much water, drought, pollution, insects and diseases. A few injuries result from nature such as broken or cracked limbs due to inclement weather.

Regardless of whether it is an injury or stress, the result is a wound to the tree, trees unlike people, cannot heal the damage. What trees do is attempt to isolate the injury by putting up barriers or walls around the damage. Therefore the damage or injury is permanently within the tree. This can lead to decay, cracks, opportunistic pathogens, rot, decline or even death. All of these leave signs.

Signs of decay include loose or missing bark, hollow areas, rotting wood, fungi at the base or on the trunk. Other indications can be weeping from the trunk or even cracks. Just because a tree has one or a combination of these signs does not mean it needs to be removed. The severity of the decay, percentage of wood affected, where the decay is in the tree and type of tree and where the tree is located are factors in determining what needs to be done..

Cracks are defects in the wood resulting in a loss of structural integrity. Cracks in the trunk are usually easier to spot but can sometimes be hidden by callus growth giving the appearance of sound wood. Cracks on either side of the trunk opposite each other are potentially very hazardous and should be looked at by an arborist immediately. Other cracks can be harder to spot especially if new growth has occurred for a few years after the crack first appeared. These can be at the base of poorly attached limbs, mid span in a branch or where codominant stems arise. In some cases a crown inspection may be needed to determine a problem. Depending on the severity and location of the crack, installation of cables to support weak limb attachments is all that is needed to reduce the risk of a hazard tree.

Opportunistic pathogens such as borers can cause weak spots in branches leading to failure or dieback. Severe outbreaks can even cause decline and death of the tree. Keeping a tree vigorous by mulching, proper pruning and watering during dry spells is the best way to minimize borer attack.

Fungi growing on the trunk, limbs or base of the tree are indications of decay inside. The extent of the decay is very difficult to ascertain. If fungi are present an arborist should be called to check the tree to determine the percent of decay inside. In trunks this can be done with a minimum of injury to the tree. . The information will determine how much structure loss exists and what steps should be taken.

Fungi that are growing at the base or on top of the soil within the root zone is again an indication of decay or rot. Left undiagnosed, could leave a tree with very little support from its roots and have a high potential for failure. In this case an arborist should perform a root crown inspection to determine the extent of decay. Done by a professional there is little injury to the root system and the information could be invaluable. Under no circumstances should trees with root decay be fertilized. Fertilizer could promote the decaying organisms and promote top growth increasing the potential of failure.

Weeping or streaking on trunks, limbs and crotches could have several causes. This can be the result of an earlier injury that has since grown over. It can again be signs of borers or an internal defect.

Identifying and correction of any of these defects is critical in keeping communities safe. Mitigating the problem may also have the added benefit in extending the life of the tree. However, sometimes the only option may be removal. Many factors go into identifying a potential tree hazard. These can include the species, growth habits, limb attachments, defects, condition of the root system and history of the tree. This with other factors such as exposure, soil, topography, and current cultural practices paint a picture of the potential of a hazard tree. Whenever a tree is suspected of being hazardous an arborist with the ability to perform a risk assessment should be called in. Only then can the best course of action be determined .Anytime structures, people and trees are in the same proximity there is a potential for damage, injury or death. Being able to recognize these signs gives you another tool to overseeing communities helping to maintaining their appearance and keeping them safe.