Firedamaged Conifers and Failure Potential

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Fire-damaged Conifers and Failure Potential
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• Old cat-face fire scars on ponderosa pine are
  often quite old and trees were likely initially
  damaged when young. Subsequent fires reburned
  the scar and may have killed newly-formed callus
  tissue but did little to effect structural
  integrity of the tree. FP is usually Low.

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• Older pine with fire-scars often have
  resin-impregnated wood which is structurally
  stronger than normal wood. Often-times old pine
  snags will remain standing for many decades at
  least partially due to resin-infusion. FP is
  Likely or Imminent depending upon deterioration
  and time dead.

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• Recent fires with heavy accumulated fuels result
  in damage greater than the historical norm. Trees
  are more likely to be affected by structural
  damage which increases their short-term failure
  potential.
• Trees are more likely to be killed by fire, and
  in the absence on structural damage, failure
  potential increases after being killed FP
  Likely and after significant decay develops, FP
  becomes Likely to Imminent.

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• Structural damage primarily to the roots, butt,
  bole and branches can increase failure potential.
  If structural damage occurs (reduced
  soundness), FP can be rated Likely or if
  sufficiently severe, or under contact/motorized
  work activity Imminent.

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Fire-caused structural damage
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Failure associated with extensive structural
damage
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• Moderate severity fires will include the entire
  range of tree damage. Represented are trees that
  were immediately killed, and trees that will die
  several years later, and trees that will survive.
  Fire-killed trees that are sound have Likely FP,
  and if unsound have Imminent FP.
• Be especially vigilant of trees that were dead
  prior to the fire or had indicators of defect
  (conks) partially consumed in the fire.

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Severe basal char and associated tree mortality.
This tree currently has Likely FP
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• Basal scorching can result in killed cambium at
  the root collar. Trees are dead but may retain a
  green crown for several years. While they still
  are sound they have Likely FP

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Checking the cambium at the root collar can be
done to confirm if the tree is dead. It is more
difficult to determine if a tree is likely to
remain alive.
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Large old pine are susceptible to fire-caused
mortality due to the accumulated duff. Mortality
is usually delayed several years.
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Pines survived ground fires when frequent
periodicity minimized accumulations of duff.
Smoldering combustion of deep accumulated duff is
lethal.
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In addition to cambium mortality, resin ducts
rupture and resin infuses the xylem, reducing
water transport function and results in moisture
stress over a period of several years. Bark
beetles cause mortality three to five or more
years after the fire. These trees should be
considered Low Failure Potential until they are
confirmed dead.
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• Until crowns fade, there will be controversy on
  whether trees are actually dead or if they will
  die.
• Trees with fire-caused structural damage should
  be evaluated based on degree of structural
  damage, with FP ratings of Likely or Imminent
  assigned appropriately.
• Fire-killed trees not having structural damage
  will eventually topple, but snag longevity is
  largely dependent upon tree size, species.
  Progression of deterioration will determine the
  change from Likely to Imminent FP rating.