Effect of Forest Fires on Trees. 197 



Character of Root System: The nearness of the roots 

 to the surface is often important, especially with swamp 

 trees whose roots are close to the surface enclosed in a moist 

 humus. In late summer or early fall when this is dry enough to 

 burn, a fire will scorch the roots, thus increasing its destructive- 

 ness. A fire in the hardwood region is seldom severe enough to 

 consume living roots, but it may kill them, thus cutting off part 

 of the source of the tree's food supply. 



On ordinary uplands the roots of most species go deep enough 

 to be out of danger of burning, but the depth of the root system is 

 determined to some degree by the site, so we might class this 

 factor of resistance partly a function o\ site. 



Origin: Tree from seed and those from sprouts have not 

 the same power of resistance at the same age. Seedlings are 

 usually slower growers than sprouts of the same species, hence it 

 takes them longer to develop thick bark. Also sprouts are gen- 

 erally thinner barked than seedlings and are attached to an old 

 stump which may be dry enough to burn, forming, moreover, a 

 convenient accumulating place for litter. When this burns it 

 generates more heat than a fire running over unobstructed ground ; 

 consequently sprouts suffer more injury. 



Small stumps cut level with the ground are soon grown over by 

 sprouts which are almost as resistant as seedlings. 



Vigor: The vigor and general health of a tree may determine 

 whether or not it withstands a given fire. Of two trees of given 

 size, age, bark thickness, etc., one dominant and fast growing, the 

 other suppressed and dying, the first will be more resistant and 

 may survive a fire that kills its weaker neighbor. 



Size: The mere fact of large size irrespective of other con- 

 siderations, is an advantage to a tree in its struggles with fire. 

 The wood of living, uninjured hardwoods seldom burns of itself, 

 but only when surrounded by burning litter. It takes more burn- 

 ing material to harm a large tree than a small one. Seldom is 

 there enough litter under hardwood stands in southern New Eng- 

 land to burn down trees more than three or four inches through 

 at the base. 



Character of the Wood: Some woods burn easier than 

 others. A species with wood that bums readily suffers more 

 than one with wood that does not. Chestnut seems to suffer more 



