I'ROTFCTIOX OF FORFSTS FROM FIRF 



Injury to the Soil 



A surface fire burns the dry leaves, 

 and usually the humus which lies on the 

 surface of the ground. Tf the trees are 

 all killed by the fire, the crown cover, as 

 well as the layer of litter and humus, 

 is destroyed, and injury to the soil fol- 

 lows this exposure to the wind and sun. 

 If the canopy is not seriously inter- 

 rupted by the fire and only the surface 

 litter and humus are burned, the extent 

 of the soil injury from one burning is 

 not serious. A very light surface fire 

 that merely burns off the dry litter 

 formed by one or two years' fall of 

 leaves has little influence on the soil ; 

 and probably no single fire, even if it 

 burned the entire humus and layer of 

 litter, would so injure the soil as se- 

 riously to affect the growth of well- 

 established trees. Normally in every 

 forest a certain amount of humus is 

 mixed with the mineral soil. This is 

 of value, both physically and chemically. 

 If a forest is burned over repeatedly, 

 however, the humus in mixture grad- 

 ually disappears, and since the leaves 

 which fall are destroyed, and no new 

 humus is formed, the soil is injured. 

 While the soil loses its supply of nitro- 

 gen and the physical benefits of humus, 

 the mineral ashes are not lost except as 

 they are subsequently leached away. 

 Nevertheless, repeated fires are very in- 

 jurious to the forest. 



Besides the direct injury to the soil 

 through changes in its chemical content 

 and physical quality, fires do further 

 damage through opening the way to soil 

 erosion. A leaf litter reinforces the 

 forest canopy in protecting the soil 

 against the impact of falling rain, and 

 the network of roots which fill tin- 

 ground hold the soil in place. The 

 greater the humus content of the soil, 

 the more absorptive the soil is. Fin's 

 leave the soil in condition to be easily 

 borne away by running water, and in- 

 crease the amount of water which runs 

 over the surface instead of sinking in. 

 If tlu 1 slopes are steep and the soil 

 easily borne awav, erosion is sure to 

 follow lires. In mountain countrv. if 



the rainfall is heavy, thin soils may 

 so badly washed as to be no long 

 capable of supporting forest growth. 



Reduction of 



Most fires kill a certain number 

 trees, or injure them so that they eitl 

 die or deteriorate in value before t 

 forest can be cut. This is particulai 

 the case with immature forests. T 

 result is a reduction in the number 

 trees which will come to maturity, a 

 hence reduction of the total increme 

 and the final yield. 



If a stand is mature and a part of t 

 trees are injured or killed, it is son 

 times possible to prevent loss by cutti 

 directly after the fire. Often, howev 

 it is not practicable to make a cutti 

 in a given part of a forest just wh 

 desired. 



When some of the trees in an imn 

 ture stand are killed or injured the 

 is always a loss. If the stand is c 

 there is a loss through cutting tre 

 which are in full productive growth. 

 the stand is allowed to grow, the fir 

 yield is reduced nearly in proportion 

 the reduction in the number of tre 

 killed in the dominant or leading da 



An owner is often confronted wi 

 the problem of dealing with an imiv 

 ture stand in which a part of the trees 

 say thirty to sixty per cent are kill 

 or injured by fire. If the remainii 

 trees are sound and thriftv, the b( 



, 



plan is usually to cut out the dead a: 

 damaged individuals, utilizing such 

 are marketable, and permit the i 

 mainder to mature, provided enouj 

 can be realized to cover substantial 

 tlie o >sl of the work. 



Effect on Reproduction 



Reproduction in the forests of tl 



country lias been more influenced 

 lire than bv any other one factor. T 

 present composition, form, density, ai 

 yield of a great many stands are due 

 the influence of fires on reproductiV 

 Repeated fires prevent reproductii 

 by destroying the seed and killing tl 

 This is well illustrated 



see< 



