FOREST FIRES 135 



problems of the forester about which the various silvicultural 

 systems described in the first chapter have developed. A careful 

 examination of any softwood forest will reveal a great many 

 deciduous seedhngs on the ground. Thgse, together with the old 

 hardwoods that the ordinary lumberman would leave, are amply 

 able to change the appearance of a softwood to hardwood forest 

 when the fo'rmer is cut off, or when the evergreens are burned. 



In a deciduous forest a surface fire may pass through and in 

 a few hours burn out except in a few dead stumps. But in a 

 coniferous forest, when a fire once gets in the duff, it becomes a 

 ground fire which may smoulder for weeks or months and eventu- 

 ally be fanned into a serious blaze by a strong wind. 



An examination of the soil just under the "duff" or leaf Htter 

 of a forest will show that the mineral particles are mixed with 

 decomposed vegetable materials. The percentage of those ma- 

 terials grows less the deeper down one digs. This top soil is 

 called humus, and it is very valuable as fertilizer, on account 

 of the nitrogen it contains, and because of its water-absorbing 

 power. One of the most serious effects of a forest fire is the 

 burning out of this humus,^ resulting in a drying out of the soil. 

 On steep slopes, especially when this binding and absorptive 

 agent has been removed, the soil is frequently washed off, leaving 

 bare ledges which will probably never again be reclothed with 

 soil. In such situations the snow melts rapidly in the spring and 

 the water flows off immediately, so that, indirectly, these fires 

 have an important bearing on water flow and freshets. 



The most severe forest fires occur on tracts which have been 

 lumbered, where the ground is covered with the tops of pines 

 and other conifers. For this reason it is very desirable that these 

 tops should be destroyed at the time of cutting, either by careful 

 burning or by lopping off the branches so that they will at once 

 come in contact with the soil and be rotted. 



Fires are not as common in New England as formerly. The 



^ Where there is considerable soil with the humus and the fire is not very severe, 

 the humus may not burn, but the removal of the litter prevents formation of more 

 humus. If fires are repeated the humus may entirely disappear. 



