PROTECTION OF FORESTS FROM FIRE 235 



ley fire in Minnesota in 1894, are swept along at a much 

 greater rate, particularly if the starting of new fires by 

 burning cinders is taken into consideration. Even in 

 extreme cases, however, it is questionable whether crown 

 fires burn at a rate of more than from 6 to 10 miles an 

 hour. 



The behavior of a crown fire depends on the character 

 of the crowns. Crown fires are mainly confined to coni- 

 ferous forests, for the leaves of hardwoods are not easily 

 ignited. 



They may, however, run through forests of mixed 

 hardwoods and conifers, and in such cases the heat gen- 

 erated is so great that the hardwood leaves are scorched 

 or killed. The velocity of the fire depends, further, on 

 the density of the stand, the thickness of the crowns, and 

 the force and steadiness of the wind. Other influences 

 affect the severity of crown fires in much the same way as 

 they affect that of surface fires. 



Damage by Fires 



The damage done by forest fires may be discussed 

 under the following heads: 



1. Death of standing trees. 



2. Injury to trees that are not killed. 



3. Injury to the soil. 



4. Reduction of the rate of growth of the stand. 



5. Effect on reproduction. 



Death of Standing Trees. Crown fires usually kill 

 outright all trees in their path. In a severe crown fire 



