BMP - Tree Risk Assessment - 78
Root Decay Evaluation. When evaluating root decay, the tree risk assessor should consider that decay in roots typically progresses from the bottom
of the root upward. Drilling and sonic techniques can help determine the
number of roots with decay and the extent of root decay within each root,
but they are not designed to quantify the amount of strength loss in the root
system. Tree risk assessors should also consider that drilling into decay in
roots can also breach CODIT wall 4, which may allow compartmentalized
decay to spread. The number of drillings should be as few as possible but
as many as needed.
Measuring Change of Lean
A changing angle of lean indicates a higher likelihood of failure. Sometimes
it is difficult to determine if a tree's lean is changing. A digital level or other
device can be used to monitor small changes in lean angle. When trunk angle
measurements are made over time, it is important that they be taken at the
same location each time. However, digital level readings taken during the
dormant season cannot be directly compared with readings taken when the
tree has foliage. The same is true during times of drought, rain, snow, or ice
glazing.
Load Tests
Load tests are used by specially trained tree risk assessors to assist in evaluating the potential for failure. There are several types of load tests: hand pull
test, measured static pull test, and measured dynamic test. Load tests do not
attempt to detect internal decay, but use deformation or deflection to detect
weakness in the structure and assess the load required to initiate the failure
process.
A hand pull test involves installing a line in the tree, and then pulling
and releasing the line several times to move the tree or branch. When testing
root and trunk stability, the line is placed high in the crown. When the line is
pulled, trunk and root plate movement is observed. Excessive trunk, root, or
soil movement may indicate instability. Branches also may be tested in this
fashion: the line is run over the branch and pulled, and the tree risk assessor
looks for movement and crack openings. This technique is most commonly
used in a pre-climbing inspection. Because the tree or branch reaction is
monitored only visually, tree risk assessors are cautioned against overloading the tree or tree part and initiating failure. The tree risk assessor should
be outside the target zone when conducting this type of test.
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Table of Contents for the Digital Edition of BMP - Tree Risk Assessment
Table of Contents
BMP - Tree Risk Assessment - Cover1
BMP - Tree Risk Assessment - Cover2
BMP - Tree Risk Assessment - i
BMP - Tree Risk Assessment - ii
BMP - Tree Risk Assessment - Table of Contents
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