PROTECTION OF FORESTS I ROM FIRE 22 



hundred feet to a number of miles in width. Irregular- 

 ities of topography and differences in the amount of 

 inflammable material cause the fire to burn more rapidh 

 in some spots than in others, so that the entire front be- 

 comes scalloped and irregular. 



Ordinarily a surface fire simply burns along the 

 ground and does not get into the tops of the trees. 

 Sometimes, however, the flames reach up into the crowns 

 and scorch them, or even ignite them here and there; but 

 such a fire still has the character of a surface fire, unless 

 it actually burns through the crowns. 



The manner of burning, the form of the fire area, the 

 rapidity of burning, and the intensity of the fire depend 

 upon the following conditions: 



1. The character and quantity of inflammable mate- 

 rial. 



2. The topography. 



3. The character of the soil. 



4. The condition of the atmosphere. 

 Inflammable Material. — The severity of a surface fire 



depends largelv on the quantity of dry material in the 

 forest. If there is an accumulation of leaves represent- 

 ing the fall of a number of vears the fire is much more 

 severe than if the litter is the result of the fall of only 

 a vear or two. The quantity of accumulated litter is 

 greatest with species having large leaves and large crowns. 

 Maple and red oak, for example, make a heavier litter 

 than ash or birch; white pine makes a heavier litter than 

 pitch pine. The severity of a fire depends further on 



