PROTECTION OF FORESTS FROM FIRE 231 



the rapidity of surface fires can be made, because it varies 

 SO greatly under different conditions. In the hardwood 

 regions of the East a surface fire seldom travels more than 

 5 miles a day, but in the coniferous forests of the West 

 instances are known where this rate of speed has been 

 more than doubled. 



Grass Fires. — In nearly all open forests there is a cer- 

 tain quantity of grass which, when dried, carries fire very 

 rapidly. In many forests the presence of grass consti- 

 tutes one of the important problems connected with sur- 

 face fires. This is particularly true in the Southern pine 

 forests. 



A grass fire is more influenced by the density of the 

 grass than by its height. Where the grass is in separated 

 patches, with no leaves or other inflammable material 

 between, it is difficult for a fire to spread. Uniformly 

 dense grass burns with the greatest intensity. High 

 grass burns with greater intensity than low grass, but the 

 fire does not usually run so rapidly. Grass a foot high, 

 if dense, may produce such a hot fire as to start a crown 

 fire. In short grass, with an ordinary wind, a fire will 

 run from 3 to 4 miles an hour; with a high wind, twice 

 as fast. The chief factors afiFecting the burning of grass 

 are its dryness and the force of the wind. Other factors 

 have their influence, however, just as they do in the 

 burning of litter. 



Brush Fires. — Bushes and small trees frequently 

 retain many dried leaves late into the fall, and in some 

 cases even into the following spring. This is particular- 



