BMP - Tree Risk Assessment - 61

Cracks also occur when stems
are torsionally stressed or are
below codominant unions that
are splitting apart. Because
internal decay may weaken
a stem, longitudinal cracks
may be associated with the
Imminent-Failure has started or is most
presence of decay. Trunks
likely to occur in the near future, even if
or branches with cracks that
there is no significant wind or increased load.
extend completely through
This is a rare occurence for a risk assessor to
the stem or branch have parencounter, and may require immediate action
tially failed and are at risk of
to protect people from harm.
complete failure. Transverse
Probable-Failure may be expected under
cracks indicate that the fibers
normal weather conditions within the
in the wood have pulled apart
specified time frame.
or buckled. They occur when
Possible-Failure may be expected in
wood is under excessive tenextreme weather conditions, but it is
sion or compressive forces.
unlikely during normal weather conditions
Cracks are a sign of localized
within the specified time frame.
failure and may indicate that
Improbable-The tree or tree part is not
tree or branch failure ranges
likely to fail during normal weather
from possible to imminent, deconditions and may not fail in extreme
pending upon loading forces
weather conditions within the specified
and tree response.
time frame.
Response growth may
Keep in mind that likelihood of failure
compensate for cracks. Intermust have a time frame specified to
nal cracks may be indicated
have meaning. The imminent category
by seams and ribs where wood
overrides the stated time frame.
has been added at the edges.
Where a shear plane crack
extends through a branch, response growth might occur in the form of compression, tension, or woundwood. Likelihood of failure should be adjusted
to account for response growth.
Growth cracks that form in the outer bark during periods of rapid trunk
growth, such as in early or midsummer, or during the rainy season in tropical
regions, are not considered structural defects.
* Seams are lines formed where two edges of bark meet at a crack or
wound. The likelihood of failure at a seam is generally considered
improbable to possible if there is solid wood behind the seam. SomePotential for failure can be classified
based on tree species, loads, response
growth, site conditions, the time frame
being considered, and other factors.
Terminology used for categorization of
the likelihood of failure is as follows:

BMP - Tree Risk Assessment

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