BMP - Tree Risk Assessment - 31

assessment process. All portions of the tree should be considered, not just
those that are associated with the most common failure patterns of the species.

Protection and Multiplicative Factors
Protection factors are structures that will reduce the likelihood of impact or the
consequences of tree failure. For people, common protection factors include
houses or other structures, and vehicles. Trees or branches that stand between
the tree being assessed and a target also may serve as protection factors. If they
are strong enough they may stop the fall of another tree or branch from above.
Protection factors are considered when assessing the likelihood of impact
and consequences. The assessor should determine if the protection is strong
enough to stop the impact. If it is, then the likelihood of impact is reduced. If
the protection is not strong
enough to stop the impact,
Tree Health vs. Structural Stability-
will it reduce the damage
Separate but Related
to the target? If it will, the
Tree risk assessors should not confuse tree
protection factor should be
health and tree stability.
taken into account when asHigh-risk trees can appear healthy in that they
sessing consequences.
can have a dense, green canopy. This may
The opposite of prooccur when there is sufficient vascular
tection factors are conditransport in sapwood or adventitious rooting
tions that may increase
to maintain tree health, but inadequate
(multiply) the target zone
strength for structural support.
and likelihood of impact.
On the other hand, trees in poor health may
If a large tree falls against
or may not be structurally stable. For
another tree, the force of
example, tree decline due to certain types
the impact may cause one
of root disease is likely to cause the tree to
or more sequential failures
be structurally unstable, while decline due
(the domino effect). This
to drought or insect attack may not.
is more likely with wet
One way that tree health and structure are
or saturated soil and spelinked is that healthy trees are more capable
cies prone to root or soil
of compensating for structural defects. A
failures. Sequential, whole
healthy tree can develop adaptive growth
tree failure may also octhat adds strength to parts weakened by
cur if newly exposed trees
decay, cracks, and wounds.
are not well adapted to the
The structural condition of a tree should
lack of shelter they have
be assessed even if the tree appears to be
following the failure of an
healthy.
adjacent tree.
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BMP - Tree Risk Assessment

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