BMP - Tree Risk Assessment - 63

Adventitious branches. Strong branch attachments form when
branch and trunk wood develop together over time. Adventitious
branches-such as epicormic shoots or watersprouts, which often
are produced after storm-related branch breakage, lion-tail pruning,
or topping-are weaker because less holding wood has formed. If
these branches are attached near a cut or broken branch end, decay
developing from the opening may reduce the strength of the attachment over time. If decay is not present, likelihood of failure in
these branches should be considered possible. If decay is present,
the likelihood of failure may be considered probable, depending
upon load and weight distribution. If significant new holding wood
has developed, the likelihood of failure may be reduced to possible
or improbable.
Multiple branches originating at one point. When several branches
originate from the same place on the stem, the branches tend to be
more weakly attached than single branches of the same size. There
is not enough space for holding wood to develop around each branch
when multiple branches arise at one level. For some species that tend
to fail at this point, the likelihood of branch failure should be considered possible to probable, depending upon load, weight distribution,
and shape of branch union. If decay is also present near the point of
multiple branch attachments, likelihood of failure is increased.
History of branch failure. Trees that have experienced branch failure
in the past may be more likely to experience branch failure in the
future. The tree risk assessor should look for patterns of weak branch
attachments, decay, decline, poor weight distribution, or other defects
associated with previous failures. Failure of additional, similarly
constructed branches is possible to probable.
Sudden branch drop (SBD). Sudden branch drop is not well understood. In some climates, tree genera such as Acer, Ailanthus,
Albizia (Paraserianthes), Andira, Delonix, Eucalyptus, Fraxinus,
Khaya, Liquidambar, Pinus, Populus, Pterocarpus, Quercus, and
Ulmus are known to drop branches unexpectedly in calm conditions
and in high temperatures. Because failure occurs without additional
load, the material properties must change or cracks must propagate
for the wood to fail. These property changes are most likely related
to changes in wood hydration. Formation of cracks may be related
to temperature changes and drying of wood. Failures typically occur
63

BMP - Tree Risk Assessment

Table of Contents for the Digital Edition of BMP - Tree Risk Assessment