Our urban forest is aging and declining at an increasing rate. At the same time society is becoming more litigious. As a result, the detection, evaluation, and management of hazardous trees is now a major concern for tree owners and arborist.
Issues of liability, responsibility and “who should pay” are frequently associated with hazard evaluations. The question of liability is one of critical importance as society tends to view trees in urban areas as different from natural areas, and inherently safer. There is a clear feeling of, “When I am in a city, it should be safe to sit under a tree.” Finally, society demands that the urban environment be safe. This requires that owners and managers make every effort to minimize any risks associated with the urban landscape.
Trees are hazardous when the failure of one or more of their parts results in property damage and/or personal injury. All trees have the potential to fail, but only a relative few actually do so. A highly trained Arborist should be hired to evaluate individual trees, assesses their hazard potential and recommend appropriate action. As trained professionals, arborists will be held to a higher standard of duty than will the average citizen.
Hazard evaluation is one component of a comprehensive risk management program, of exercising the duty of care. By examining trees, rating their likelihood of causing damage and injury – and taking action to abate the hazard, arborists act to reduce the risks associated with trees. In this manner, the most significant hazards, those trees with the greatest likelihood of failure and injury, may be abated first. Other aspects of a tree hazard evaluation such as record keeping and application of sound management in abatement all act to reduce liability.
By preventing and/or eliminating dangerous situations, hazard tree management creates a safer environment. In so doing, the liability of the tree owner is reduced. Hazard tree assessment is a tool for scheduling and prioritizing work, allowing a greater degree of management efficiency and flexibility. Also, by identifying and correcting structural defects, tree longevity is enhanced.
Responsibilities With Respect To Hazardous Trees
Property Owners / Property Managers: The law is quite simple and clear when it comes to the property owner’s or manager’s legal responsibility in managing trees in urban areas.
The property owner / manager has the obligation to periodically inspect trees for unsafe conditions and, the property owner must correct unsafe conditions immediately when they are discovered.
Identifying and managing the risks associated with trees is a subjective process. Since the nature of tree failures remains largely unknown, our ability to predict which trees will fail and in what fashion is limited. As currently practiced, tree evaluation involves examining a tree for structural defects, associating those defects with a known pattern of failure and rating the degree of risk.
Tree hazard assessment involves three components:
- a tree with the potential to fail,
- an environment that may contribute to that failure, and
- a person or object that would be injured or damaged (i.e. the target).
By definition, a hazard situation requires the presence of both a defective tree and a target. Unless a target is present, a tree cannot be hazardous. As a result, assessing hazard is not limited to evaluating failure potential. Hazard evaluation must consider the potential presence of a target.
Managing Tree Populations To Prevent Liabilities
Inspections: Trees should be inspected annually and after major storms for structural defects. A more frequent inspection program should be established in high use areas or in areas with a history of tree failures.
Remedial Treatment (Abatement): Hazardous tree conditions should be corrected through accepted arboricultural practices such as tree removal, pruning, cabling, bracing, guying, etc.
When targets can be moved or activities relocated, it is considered an acceptable management practice. Sometimes – barriers (limiting entry and access) and signage (disclosing and warning of the hazard) will reduce liability – but not eliminate the risk.
Avoidance of Liabilities: accepted arboricultural procedures should be followed to prevent tree liabilities. This includes proper pruning practices (avoiding topping and flush cuts) and proper cabling, root pruning, fertilization, and etc. Standards published by the National Arborist Association in accordance with ANSI Standards should be followed for all tree maintenance.
Documentation: Inspections and all tree maintenance/remedial treatments should be documented in writing. Information should include the name of the arborist performing the inspections, date of inspection, description of hazardous conditions, maintenance performed to correct unsafe conditions, and date and names of individuals who corrected the condition. Verbal notification is not sufficient
Many defects including dead branches, hangers, and “V” crotches can be detected and fully assessed based solely on a visual inspection. Sometimes this may require the inspection of the canopy from above ground by a climber or aerial lift truck. To evaluate the impact of wood decay and root disorders, a more thorough examination is required. For wood decay, evaluation involves probing the stem or branch to determine the extent of decay and then calculating the strength loss resulting from deterioration of the woody tissue. For root disorders, the root collar area may require excavation and the buttress roots examined for discoloration and decay.