234 BURNING OF PASTURE LANDS 



than a surface fire and usually kills all vegetation that is present. 

 Ordinarily a ground fire covers only a few acres. 



A crown fire is one which races through the tops of the trees 

 at high speed. It is the most destructive of all, as it kills not 

 only practically all the trees that stand in its path but the 

 herbaceous and brush cover too. Crown fires usually leave the 

 soil sterile, so that for years it is incapable of supporting the 

 higher types of vegetation. 



The damage to the large trees caused by surface fires is com- 

 paratively small; but, if there is a considerable amount of in- 

 flammable material on the ground, the fire gains in intensity, and 

 there is danger that the flames will spread to some low-limbed 

 tree and thence into the tops of the trees and start a crown fire. 

 If the area is grazed by livestock, and if the weeds, grass, and 

 leafage of shrubs have been devoured to a considerable extent, 

 not only is the danger of damaging surface fires reduced, but 

 there is much less opportunity for the starting of the more 

 destructive ground and crown fires. 



For the same reason driveways over which large numbers of 

 livestock are moved, and which are almost always closely grazed, 

 tend to prevent fires from spreading to adjacent areas where the 

 forage may not have been closely utilized. The fact that many 

 of these driveways are located on ridges and along roads where 

 lines of defense would have to be estabhshed to prevent the 

 spreading of a fire greatly adds to their value for this purpose. 

 It is recorded that many sheep driveways have been sufficient 

 to stop fires which would otherwise have burned unchecked. 



Trails made by Uvestock in going to and from water, salting 

 places, and feeding grounds are likewise valuable for fire-fighting 

 purposes, both because they often check fires, and because they 

 permit men and supplies to be taken into areas where travel 

 would otherwise be difficult if not impossible. Trails, con- 

 structed to open up unutilized range, furnish important means of 

 access if fires occur. Likewise the development of stock- 

 watering places in regions where water is scarce often enables 

 fire-fighting crews to estabhsh camp much more advantageously 

 than would otherwise be possible. 



