ISA Arborist Certification Tree Risk
Assessment Exam-Graded A
is the likelihood that an entire tree, or part of a tree, will break and fall. In evaluating a
tree's failure potential, the arborist must consider a number of factors, including the
species, growth habit, quality of branch attachments, condition of the root system, lean,
and the history of the tree and site. - ANS-Failure potential
- construction, grade changes, and trenching within the root zone
- removal of adjacent trees that previously served as a wind buffer
- replacement of sidewalks and root loss (root pruning)
- failure of nearby trees caused by root disease - ANS-The arborist should consider the
history of the site and how it affects tree stability. Following are some of the factors that
should be noted:
Targets are people and/or property that could be damaged or injured if the tree failed. If
there is no target, there is no risk, because if the tree fails, no damage would occur. -
ANS-Failure Targets
component of tree risk assessment. All trees have the potential to fail. As trees grow
larger and mature, and assuming there are targets present, the degree of risk
increases. - ANS-tree risk management
that can lead to failure are not always visible, especially those inside the tree or beneath
the ground, and the forces of nature are unpredictable. - ANS-Structural defects
tree species
what is normal and abnormal growth
structure and form
species' primary failure patterns - ANS-It takes a trained eye to discern the difference
between a minor defect and significant weaknesses that are likely to result in tree
failure. The arborist must be familiar with:
Many trees develop lean as they grow into open light areas and away from larger trees
or structures. In these cases, the trees develop reaction wood to support the tree in a
leaning position. Such trees are stable in normal conditions; however, they often are
more likely to fail when loaded with rain, snow, or wind than upright trees. - ANS-
Leaning Trees
having a diameter that gradually decreases from the base to the tip, are stronger than
stems with poor taper - ANS-Taper
, movement in wind and is enhanced by presence of lateral branches low on the stem.
Trees growing in the open tend to have good taper, while those growing in stands have
poor taper. - ANS-Taper develops in response to
Lack of a trunk flare, discolored or loose bark, and indentations created by circling roots,
wounds, and seams are all defect indicators. It may be necessary to dig away mulch
and soil to find and inspect the root collar. - ANS-trunk flare
codominant stems and included bark - ANS-When performing a risk assessment, an
indication of a significant defect is
Dead branches within the canopy of a tree are probably most obvious sign of risk. -
ANS-Dead Branches
Cracks or separations in the soil may indicate soil having from excessive movement of
roots which can be a warning sign for failure if the tree is leaning. - ANS-Root Failure
An observant arborists may be able to detect internal defects where the stem exhibits
irregular growth. Asymmetric shapes may be caused by the trees formation of reaction
wood and may be an indication of an internal problem. Other obvious signs are fungal
fruiting bodies and cavaies. - ANS-Decay Indicators
Watch for longitudinal cracks or splits on the trunk or major branches. Cracks that start
at a branch union may be especially hazardous. Cracks in decayed stems or branches
may indicate imminent failure. - ANS-Cracks or Splits
A major defect - ANS-Codominant Stems
More prone to taper - ANS-Poor Taper
Wounds, weak or damaged limbs, and decay may be the result of poor pruning or other
misguided practices. Root loss can result from construction, trenching, grade changes,
and soil compaction. - ANS-Human Caused effects
Unusual bulges and swilling in trunks or stems may be indicators of internal decay. The
swelling is usually formed around an internal cavity to compensate for wood and
strength loss caused by decay. - ANS-Unusual Bulges
Externally visible defects include cankers and wounds. - ANS-Cankers and Wounds
Wood decay is caused by certain fungi, which may or may not form conks or
mushrooms (fruiting bodies). Conks and mushrooms are two types of fungal
reproductive structures. If they are attached to a tree, this is an indication of internal
decay. However, a tree can have decay without the presence of conks or mushrooms
on the outside. - ANS-Wood Decay
Assessment Exam-Graded A
is the likelihood that an entire tree, or part of a tree, will break and fall. In evaluating a
tree's failure potential, the arborist must consider a number of factors, including the
species, growth habit, quality of branch attachments, condition of the root system, lean,
and the history of the tree and site. - ANS-Failure potential
- construction, grade changes, and trenching within the root zone
- removal of adjacent trees that previously served as a wind buffer
- replacement of sidewalks and root loss (root pruning)
- failure of nearby trees caused by root disease - ANS-The arborist should consider the
history of the site and how it affects tree stability. Following are some of the factors that
should be noted:
Targets are people and/or property that could be damaged or injured if the tree failed. If
there is no target, there is no risk, because if the tree fails, no damage would occur. -
ANS-Failure Targets
component of tree risk assessment. All trees have the potential to fail. As trees grow
larger and mature, and assuming there are targets present, the degree of risk
increases. - ANS-tree risk management
that can lead to failure are not always visible, especially those inside the tree or beneath
the ground, and the forces of nature are unpredictable. - ANS-Structural defects
tree species
what is normal and abnormal growth
structure and form
species' primary failure patterns - ANS-It takes a trained eye to discern the difference
between a minor defect and significant weaknesses that are likely to result in tree
failure. The arborist must be familiar with:
Many trees develop lean as they grow into open light areas and away from larger trees
or structures. In these cases, the trees develop reaction wood to support the tree in a
leaning position. Such trees are stable in normal conditions; however, they often are
more likely to fail when loaded with rain, snow, or wind than upright trees. - ANS-
Leaning Trees
having a diameter that gradually decreases from the base to the tip, are stronger than
stems with poor taper - ANS-Taper
, movement in wind and is enhanced by presence of lateral branches low on the stem.
Trees growing in the open tend to have good taper, while those growing in stands have
poor taper. - ANS-Taper develops in response to
Lack of a trunk flare, discolored or loose bark, and indentations created by circling roots,
wounds, and seams are all defect indicators. It may be necessary to dig away mulch
and soil to find and inspect the root collar. - ANS-trunk flare
codominant stems and included bark - ANS-When performing a risk assessment, an
indication of a significant defect is
Dead branches within the canopy of a tree are probably most obvious sign of risk. -
ANS-Dead Branches
Cracks or separations in the soil may indicate soil having from excessive movement of
roots which can be a warning sign for failure if the tree is leaning. - ANS-Root Failure
An observant arborists may be able to detect internal defects where the stem exhibits
irregular growth. Asymmetric shapes may be caused by the trees formation of reaction
wood and may be an indication of an internal problem. Other obvious signs are fungal
fruiting bodies and cavaies. - ANS-Decay Indicators
Watch for longitudinal cracks or splits on the trunk or major branches. Cracks that start
at a branch union may be especially hazardous. Cracks in decayed stems or branches
may indicate imminent failure. - ANS-Cracks or Splits
A major defect - ANS-Codominant Stems
More prone to taper - ANS-Poor Taper
Wounds, weak or damaged limbs, and decay may be the result of poor pruning or other
misguided practices. Root loss can result from construction, trenching, grade changes,
and soil compaction. - ANS-Human Caused effects
Unusual bulges and swilling in trunks or stems may be indicators of internal decay. The
swelling is usually formed around an internal cavity to compensate for wood and
strength loss caused by decay. - ANS-Unusual Bulges
Externally visible defects include cankers and wounds. - ANS-Cankers and Wounds
Wood decay is caused by certain fungi, which may or may not form conks or
mushrooms (fruiting bodies). Conks and mushrooms are two types of fungal
reproductive structures. If they are attached to a tree, this is an indication of internal
decay. However, a tree can have decay without the presence of conks or mushrooms
on the outside. - ANS-Wood Decay
