Evaluation of the hazard potential of urban trees is an important role for any Arborist. Trees become hazardous when the failure of their parts results in personal injury or property damage. Identification and correction of structural defects can reduce the potential for failure and prolong the life of the tree. There are three components that the arborists will consider when conducting tree inspections: the potential of the tree to fail, the environment that may contribute to failure, and the potential target. Each of these factors impacts the hazard rating of the tree.
When evaluating the potential of a tree to fail, we examine the species, growth habits, branch attachments, defects, condition of the root system, lean, and the history of the tree. Size is also considered in the evaluation of a tree's potential to fail. Obviously, the damage potential is far greater for large limbs than small branches.
The environment plays a critical role in the potential for tree failure. Most tree failures occur during, or as a result of, storms. Exposure to winds, lightning, and rainfall are all considered when making tree inspection. Other environmental factors such as soil conditions, slope, construction, and nearby trenching can also affect the likelihood of failure. By definition, if there is no potential target, a tree does not present a hazard. Potential targets may include structures, vehicles, or people. Because they are fixed, structures are relatively easy to assess. However, in determining the likelihood of a failed tree or branch striking a person, factors such as the frequency and intensity of use of the site must be considered. Almost all trees pose some risk of failure. As trees grow larger and more mature, the degree of risk increases. A thorough inspection of trees requires a fundamental knowledge of tree structure and physiology. It takes a trained eye to discern the difference between a minor flaw and a possible hazard. We are fully trained to evaluate the level of risk trees represent and make recommendations on ways to reduce that risk.