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increased because the tree's ability to compensate for strength loss by increasing diameter growth is severely limited. The likelihood of failure depends on the
amount and location of sapwood that is missing, the amount and type of
internal decay, tree size, lean, weight distribution, and exposure to loads.
Tree Architecture
Tree growth and branching characteristics can affect how a tree moves in the
wind, how the load of the crown is distributed, and, ultimately, the tree's stability. Problems with other structural defects may become more significant
when tree architectural abnormalities are present. Tree architectural characteristics to consider include the following:
Lean
Lean is the angle of the trunk measured from vertical. For most trees, lean
develops as the tree grows away from neighboring trees or structures, toward
light. Trees that lean may be stable for long periods of time. However, leaning trees can be less stable than vertical trees because weight is unequally distributed over the trunk and root system. Trees with uncorrected leans and
leaning trees on slopes with saturated or unstable soils are often less stable
than straight trees or those with corrected leans.
Critical lean is often difficult to assess, and often is directly related to the
growth characteristic of a species. Conifers generally exhibit a geotropic
growth response with respect to the force of gravity. Deciduous species
exhibit a phototropic growth in response to sunlight. The amount of lean in
conifers that would be of concern would be less than that for deciduous trees.
In all cases, the condition of root anchoring is a critical consideration. Signs
of root lifting on the backside of the lean, such as mounding, soil cracking,
and/or exposed roots, may indicate a sign of tree failure in progress. Conversely, a significant lean with no signs of root movement and generally stable soil conditions should reduce risk of failure.
Trees may also lean because of a partial failure of the lower stem or roots,
or soil conditions that allow excessive root movement. Trees that increase in
lean over a short period of time are of concern and should be examined
promptly. Lifting of the soil on the side of the tree opposite of the direction
of lean, or a depression on the side of the lean, may indicate that the roots
or soil are failing. Lean angle can be determined using several means, including interpretation of photographs or use of a digital level. The residual
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Table of Contents for the Digital Edition of BMP - Utility Tree Risk Assessment
Table of Contents
BMP - Utility Tree Risk Assessment - Cover1
BMP - Utility Tree Risk Assessment - Cover2
BMP - Utility Tree Risk Assessment - i
BMP - Utility Tree Risk Assessment - ii
BMP - Utility Tree Risk Assessment - Table of Contents
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