252 FOREST PROTECTION 



the main fire may be one to two hundred feet above the ground. 

 They are restricted almost entirely to coniferous forests which 

 have inflammable foliage and retain it throughout the year; 

 although there are certain species of broadleaved shrubs and 

 dwarf trees with evergreen foliage of an inflammable char- 

 acter upon which crown fires might feed. In the case of 

 broadleaved species the foliage, while on the trees, remains 

 green and does not occur in such close arrangement as in the 

 case of conifers. One instance is known where a crown fire 

 ran through a stand of oak and chestnut. The fire occurred 

 in the fall and the chestnut trees due to injuries by chestnut 

 blight retained the dry chestnut burrs and much of the 

 foliage. The foliage of the oak also had shriveled up and 

 remained on the trees. This combination furnished enough 

 inflammable material for the crown fire. 



Crown fires apply heat to the tender twigs throughout the 

 top and usually are fatal to the trees affected. 



A crown fire is accompanied by a surface fire. In fact the 

 burning material on the ground greatly assists in creating a 

 steady volume of heat and enables the fire to progress, as a 

 crown fire, over places where without this assistance it would 

 stop. Advantage is taken of this fact in fighting crown fires 

 by burning off the inflammable surface material ahead of the 

 crown fire. 



Fires ordinarily start as surface fires. Then where deep 

 deposits of humus are reached a ground fire develops. 



Crown fires sometimes originate as a result of lightning 

 striking some tall dry stub and setting it afire, or more com- 

 monly start from a surface fire. Dry moss hanging from the 

 trunk or branches, inflammable pitch on the bark, the burning 

 tops of a mass of reproduction, or even the flames from a hot 

 grass fire may serve to carry the fire upward and ignite the 

 crowns. 



