BMP - Tree Risk Assessment - 77

from the sending point to the receiving point. If a crack, cavity, or decay is
present, the sound travels around the defect, increasing the transmission time
(time of travel) from the sending point to the receiving point, as compared
to the transmission time through wood with no defect. The device, however,
cannot distinguish the type of defect (decay, cracks, embedded bark, or cavities) that increased the transmission time.
Measuring the transmission time between two points can be a quick test
to reveal the presence of cracks or decay between the two points. However,
conducting only one test may miss even major defects; tests at additional
points are needed to provide a comprehensive inspection. Thus, two sets of
points, forming perpendicular lines, are considered the minimum by many
operators in order to detect large, centrally located defects. In addition, reference values are needed for any measurement.
Sonic tomography instruments use measurements between many points
to create a two- or three-dimensional picture (tomogram). By comparing the
results of all time-of-travel measurements, it is possible to detect and map
defects within the trunk. The tomogram illustrates the remaining load-carrying
parts of the inspected cross section. The resolution of tomography is directly
related to the number of sensors used on a tree. In contrast to drilling, sonic
devices have substantially less risk of breaching CODIT wall 4.

Root Assessment
Root Inspection and Evaluation. The extent of damage or decay in tree
butts, buttresses, and roots is difficult to evaluate in a basic inspection because
most roots are beneath the soil surface and root architecture is not visible.
Several types of evaluations can be conducted on roots to inspect for decay.
The simplest is the visual assessment of buttress roots at the basal flares, or
when the top surfaces of the roots are exposed. When not exposed, the tree
risk assessor would first need to excavate soil or other materials covering
the root collar to conduct the assessment. This process is called root collar
excavation (RCX). At a minimum, the RCX should reveal the top of the buttress roots to the point where the root is nearly horizontal, or follow roots a
distance equal to or greater than the trunk diameter. Depending upon the goal
of the assessment, the excavation may need to continue further out along the
root. The least injurious method of excavation available should be used. This
may involve the use of high-pressure air or water. If necessary, hand tools
can be used. Care must be taken not to damage the roots or trunk during the
excavation process. After excavation, roots can be inspected for evidence of
cutting, injury, decay, response growth, or other conditions.
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BMP - Tree Risk Assessment

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