PROTECTION OF FORESTS FROM FIRE 233 



very slowly, and a deep layer of partially decayed organic 

 matter accumulates, often to a depth of from 2 to 3 feet. 

 This material absorbs moisture with avidity and retains 

 it tenaciously. Consequently, in moist seasons it is not 

 readily ignited. In some seasons, however, it becomes 

 thoroughly dry and will burn. A fire in this peaty sub- 

 stance burns slowly, but with very intense heat, and is 

 exceedingly difficult to extinguish. Ground fires in the 

 Adirondack^ have been known to burn all winter, creep- 

 ing along under a deep layer of snow. 



Ordinarily a ground fire does not cover more than a 

 few acres in a day. Frequently, however, there is upon 

 the surface a large amount of dry debris or small coni- 

 ferous trees so that there accompanies the ground fire 

 a surface fire or a brush fire, or both, and occasionally 

 a crown fire. 



Crown Fires. 



Crown fires are those which burn through the crowns 

 of the trees. They almost invariably start from surface 

 fires. Occasionally, however, they are started when light- 

 ning strikes and ignites a dry stub or resinous tree sur- 

 rounded by a dense stand of conifers. If the crowns 

 are of such a character that they will burn, they may be 

 easily ignited by the flames which rise from a surface 

 fire. Sometimes a crown fire is started by the flames 

 from a burning clump of young growth, and where the 

 trees have exuded resin or there is loose inflammable 

 bark, a crown fire may be started by the flames running 

 up the trunk. 



