Crown scorch

n. The portion of a tree’s foliage that is killed by heat during a fire.

 

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Crown scorch refers to the portion of the tree’s foliage that is killed by heat transferred via convection during a fire.  Almost immediately after a fire, scorched foliage will appear brownish red.  Crown scorch is usually expressed either as a percentage of the pre-fire crown volume or as a percent of the pre-fire crown length.

 

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For most species, crown scorch and crown kill are the same.  However, some species have thick buds (for example, longleaf pine and ponderosa pine) or woody structures around the buds (such as western larch) that help protect the living tissue from heat injury. Other species, such as redwoods and many hardwoods, can also recover from crown scorch by means of epicormic sprouting from dormant buds. In these species, it is possible to have crown scorch without crown kill.  For species with thick buds, this lack of crown kill is often evidenced soon after a fire by a thin area of the crown, usually just below any remaining green foliage.  If there is a section of the crown that seems to have lost most of its needles, the foliage in that area was likely scorched and killed, but the buds were not killed.  Therefore, it is possible for this section of the crown to recover from the fire; the tree limb is still functional and is able to shed dead needles through abscission. On the other hand, dead limbs cannot abscise needles, so they remain on the limb.  This difference between crown scorch and crown kill can be more easily seen immediately after the following spring bud break.  Areas of the crown that were killed will remain brown, whereas areas that were scorched but are alive will have tufts of green at the end of limbs where the current needle flush is occurring. For species that sprout from epicormic buds or are deciduous, crown scorch should be estimated before leaves drop from the trees too determine crown scorch.