BMP - Tree Risk Assessment - 48

Work Prioritization
With a single, privately owned tree, there is little need for the prioritization
of work. The owner will decide what action to take and schedule the work.
The exception is with extreme-risk trees, where the tree risk inspector should
recommend that the work take place as soon as possible and the target zone
may need to be restricted immediately.
With populations of trees, such as in municipal or utility applications,
work may need to be scheduled well in advance. The risk assessment can
be used to establish the work priority to mitigate the highest risk situations
first. If a tree with an extreme risk is discovered, the owner/manager should
be notified promptly, and action should be taken as needed. In the rare event
that failure is in progress, immediate action may be needed to restrict access
to the target zone and notify the client. Trees with lower levels of risk can be
scheduled on an appropriate maintenance cycle.
Clearly it makes sense to mitigate high-risk trees before moderate-risk
trees. Judgment should be exercised in prioritizing mitigation within groups
of trees rated at the same level of risk. Factors to be considered include:
location, targets, tree or part size, and the logistics of mitigation.

Residual Risk
Residual risk is the risk remaining after mitigation. Following any mitigation action, there is a residual risk posed by that tree. With tree removal,
that residual risk is brought to near zero; however, even stumps can pose
a tripping risk. The level of residual risk needs to be acceptable to the risk
manager/owner. Some countries follow the principle of " as low as reasonably
practicable " (ALARP). To meet this principle, one must demonstrate that the
cost involved in further reduction of risk would be grossly disproportionate
to the benefit gained. ALARP is sometimes applied in situations where large
populations of trees are being managed.
In general, if the residual risk following mitigation would exceed the
tolerance of the client, the specified treatment might not be the best course
of action. As previously noted, however, tree removal should not be recommended without due consideration of the benefits that would be lost.
While the highest risk factor is often the focus of remedial action, the tree
risk assessor may recommend mitigating options for each condition evaluated,
and estimate the residual risk following those actions. The level of residual
risk should be part of a complete report so that an informed decision can be
made regarding the mitigation options.
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BMP - Tree Risk Assessment

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