SEAMS
A vertical seam in a trunk suggests an internal defect, usually an old wound.
The wound creates a weakened place in the wood that is prone to cracking and
splitting, especially when the trunk is under stress by winds or abrupt changes
in temperature. "Frost cracks" or seams are the outward signs of
these internal splits. |
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CROWN VIGOR AND FORM
Crown condition and tree form often indicate the general health of a tree.
Crown characteristics that may indicate an unhealthy or unsafe tree include
dieback, V-shaped forks, and lopsidedness. Dieback, characterized by branches
in the upper crown dying from the top down, is usually a response to stress
(Figure 5). Repeated insect defoliation, drought, soil compaction, or root
disease are common types of stress. Secondary pests, such as insects and fungi,
are able to invade and further injure stressed trees. Trees can recover from
dieback if it has not progressed too far before the source of stress is
eliminated (e.g., population of insect defoliators collapses). Trees with
advanced crown decline, however, will die and should be removed.
V-shaped forks are weaker than broader angles and are more likely to split. Ice
storms, heavy wet snow, or high winds often trigger such a failure. Elm, oak,
maple (especially silver maple), yellow-poplar, and willow are especially prone
to breakage at weak forks (Figure 6). |
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Figure 5 - Dieback of paper birch. Dead
branches in upper crown indicate tree is under stress due to such factors as
drought, disease, insect defoliation, soil compaction or exposure.
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Figure 6 - Trunk seam or vertical crack
indicates point at which tree is liable to split during windstorm or under
heavy snow load. |
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When trees are removed for a new campsite,
crowns of hardwood trees on the edge of the campsite begin to grow into the
opening, creating a lopsided crown. Large limbs develop over the campsite and
the trees will tend to fall into the campsite should failure occur. Lopsided
crowns may develop also along hiking or ski trails and roads.
Branches that break off and become lodged in the crown pose a serious risk
because they may be easily dislodged during relatively light winds.
Leaning trees may represent a hazard if the direction of lean is toward a
potential target (Figure 7b). Generally, trees that lean more than 15 degrees
off the vertical should be removed. Trees that have always grown with a lean
are considerably less hazardous than trees that originally grew straight but
subsequently developed a lean due to wind or root damage. The general growth
form of a tree and any uplifted soil on the side of the tree opposite the lean
give clues to when the lean developed. |
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