One of the most glaring word uses in risk assessment is the word “hazard.” The word hazard, for both lay-people and professionals denote that some threshold of risk has been surpassed. Hazard also conveys the immediacy of structural failure as determined by a tree professional. Within community forestry, it is critical that the word “hazard” be used only in association with situations where an actual hazard has been identified. The hazard concept demands a completed evaluation and assessment of risk which reaches a management threshold where the situation cannot be allowed to continue.

Beware of the misuse or overuse of the word “hazard.” Every landscape and tree situation has risk involved. Nothing is risk free. All trees carry a given amount of risk. That level of risk under some management regimes would be hazardous while under other management objectives would be acceptable risk. Some situations allow more risk to be accepted and managed, while other situations would call for immediate removal and risk reduction.

Because all trees have risk associated with them, discussion of the structural integrity of a tree should assess the level of risk present. It is the amount of risk present, the perceptions of the risk manager, and the willingness to accept or not accept a given level of risk that determines hazard. Any tree is not necessarily hazardous, but all carry some level of assessable risk that professionals can estimate.

Because a hazard condition has two components (a major structural fault and a target), let us
examine structural faults and tree defects. Structural defects are dependent upon fault length, width,
and depth, tree species, tree vigor, and associated compounding structural problems. Hazard assessment
is only about structure, not about aesthetics or biology. Structural defects can include large vertical (longitudinal) cracks, large decayed areas, included bark zones, narrow crotches or forks, dead
wood and branches, large cavities, large leans, major root damage, horizontal (tangential) cracks,
poorly connected living branches, pest damaged or modified areas, and mis-proportioned crown root
ratio and stem strength for the given wind and gravity loading conditions. There are many unique
forms of tree failures.