148 PRINCIPLES OF AMERICAN FORESTRY. 



land is at least 185 feet board measure per acre, it is plain 

 that the loss to the people on the 10,000,000 or more acres 

 of these cut-over lands is very large. 



It is impossible for fires to run over any forest land with- 

 out doing great injury. The amount of damage done by 

 them is difficult to estimate, and varies much according 

 to the time of year, the age and condition of the trees, 

 the soil and the severity of the fire. 



Forest fires are sometimes grouped into the three fol- 

 lowing classes: 1. Underground Fires, that do not 

 show much on the surface, but which destroy the roots 

 of trees and greatly injure the soil. 2. Surface Fires, 

 which bum the leaves and grass in the woods, and do much 

 damage by destroying the forest floor and killing the 

 young seedlings. 3. Crown Fires, which run in the 

 crowns of the trees, and when once started are almost 

 irresistible. The latter is one of the worst forms, and 

 is generally accompanied by surface, and often by under- 

 ground, fires. 



The Killing of Mature Trees by any of these three 

 kinds of fires entails but a shght loss comparatively to the 

 timber, providing it is accessible to market, as the trees 

 can be cut the following winter. But fires that kill the 

 mature growth generally do great damage by killing the 

 young growth and destroying the forest floor. Timber 

 that is allowed to stand more than one or two years after 

 being killed by fire generally suffers much from insects 

 and fungus diseases. This is most evident in the case 

 of White Pine, Birch, Poplar, and similar soft woods, 

 but even hard woods are injured by insects if allowed 

 to stand long after being killed. 



The Killing of Half-Grown Trees by forest fires causes a 

 loss that amounts not only to the value of the timber 

 trees, but to the value of the seeding and shading 

 trees and the forest floor. The value of the trees alone 



