BMP - Tree Risk Assessment - 49

Inspection Frequency and Timing
Timing of the initial risk assessment and frequency of future assessments
is often not at the discretion of the tree risk assessor. However, after a tree
has undergone the initial assessment, an inspection frequency should be
recommended based upon the level of risk/residual risk and the goals of the
client. The time between assessments is known as the inspection interval.
It is best to reassess trees on a regular, recurring basis because site and tree
conditions change over time.
The inspection interval typically ranges between one and five years, but
inspections may be more or less often, depending upon the age of the tree,
level of risk, specific conditions, client goals and resources, or regulations.
For example, a low-risk tree may be assigned an inspection interval of three
to five years, or perhaps more. For a high-risk tree, an inspection period of
several months to one year may be recommended. Generally, it is a good idea
to inspect trees with known structural weaknesses and high-value targets after
major storms or other exceptional events on the site (such as forest clearing, trenching, or other construction work) to identify damage or changes in
condition that may have occurred.
The time between tree risk assessments conducted by or on behalf of
municipalities, utilities, and other entities that manage large populations of
trees is often defined by risk managers acting on behalf of those agencies or
their controlling authority. Public agencies, utilities, and large property managers may identify zones of similar tree population, site usage, and facility
type. The inspection interval for each zone is then specified. Zones of higher
priority should be inspected more frequently than zones with lower priority.
Scheduling assessments in a specific season can aid the assessment. For
instance, the crowns of deciduous trees are more easily assessed for failure
likelihood in the winter than when in full leaf in the summer, because the
branch structure and unions are more easily seen. If a particular decay fungus
produces annual fruiting bodies (conks, brackets, or mushrooms) at specific
times of year but the structures subsequently degrade or disappear, identification of that decay will be easier if the inspection is scheduled to correspond
with emergence of the fruiting bodies. Staggered inspection intervals, such
as every 8 or 16 months, will allow the tree risk assessor to see the trees in
different seasons. For the utility arborist, assessments can be combined with
periodic line clearance pruning operations or conducted as separate activities.
Commercial arborists may include assessments as a part of a plant health
care program. Municipal arborists may include inspections as a component
of cyclic pruning programs, or as part of routine citizen response inspections.
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BMP - Tree Risk Assessment

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