240 THE PRINCIPLES OF HANDLING WOODLANDS 



It is not only in shortening life and in reducing 

 growth that fires injure trees; the quality of the product 

 is also affected. Even where there is no injury by in- 

 sects or fungous disease, a fire that has killed one side of 

 a tree usually leaves its scar. In time the wound may 

 entirely heal over, but there is nearly always a point of 

 weakness which may ultimately cause a seam or wind 

 shake, and unfit the butt log for lumber. If rot sets in, 

 it may spread throughout the trunk and make the tree 

 worthless, even if it does not kill it. 



Injury to the Soil. A surface fire burns the dry 

 leaves, and usually the humus which lies on the surface 

 of the ground. If the trees are all killed by the fire, the 

 crown cover, as well as the layer of litter and humus, is 

 destroyed, and injury to the soil follows this exposure to 

 the wind and sun. If the canopy is not seriously inter- 

 rupted by the fire, and only the surface litter and humus 

 are burned, the extent of the soil injury from one burn- 

 ing is not serious. A very light surface fire, that merely 

 burns off the dry litter formed by one or two years' fall 

 of leaves has little influence on the soil; and probably no 

 single fire, even if it burned the entire humus and layer 

 of litter would so injure the soil as seriously to affect 

 the growth of well-established trees. Normally in every 

 forest a certain amount of humus is mixed with the min- 

 eral soil. This is of value, both physically and chemi- 

 cally. If a forest is burned over repeatedly, however, 

 the humus in mixture gradually disappears, and since 

 the leaves which fall are destroyed, and no new humus is 



