Bark char [Bole char]
n. The blackened residue resulting from incomplete combustion of the bark.
Bark char, also called bole char, is used as an indicator of the length of time a tree bole has been exposed to the flames and high temperatures of a fire. Bark char correlates to the heat transferred into the tree and has been used to estimate cambium injury. Bark insulates the cambium and helps to protect it from heat injury. The greater the bark thickness, the longer a tree can be exposed to high temperature without cambium mortality. Bark char on trees with thin bark can indicate cambium injury. However, bark char on trees with thick bark is not always a reliable indicator of the condition of the underlying cambium (Hood and others 2007).
Several studies have found bark char or bark char classes to be a significant predictor of post-fire tree mortality (see Peterson and Arbaugh 1986, 1989; McHugh and Kolb 2003; Keyser and others 2006; Sieg and others 2006).
Bark char classes were developed by Ryan (1982b) to aid in estimating cambium injury (see table below). The accuracy of these codes has not been fully tested, and they therefore should not be used as sole indicators of cambium status, especially for trees with thick bark.
from Ryan (1982b)
Light bark char. Bark is not completely blackened and species is still identifiable based on bark characteristics; edges of bark plates blackened.
Moderate bark char. Bark is uniformly black except possibly some inner fissures; bark characteristics still discernable.
Deep bark char. Bark has been burned into, but not necessarily to the wood; outer characteristics are lost.