48 



is practically always at the base of the tree, the most 

 valuable timber is destroyed. Hence, it can be seen 

 that the damage resulting from the scarring of trees by 

 light surface fires is tremendous after wood-destroying 

 fungi gain an entrance. 



(7) Reduction in D ensity of Stand 



Logging is not practicable in the Sierra region if 

 the merchantable timber is much less than 8,000 board 

 feet per acre. Stands which are almost on the border 

 line of the required merchantable volume, may be re- 

 duced below it by one or more surface fires. If a few 

 large mature trees are killed fssom time to time by TBurn- 

 ing down or heat killing, and reproduction is prevented, 

 a reduction in the density of the stand must necessarily 

 take place. -ISxamples of this are found in the extensile 

 brushy areas within the timber belt of California which 

 today bear only scattered large trees. 



( 8 ) Change s in Composition 



Due to variance in fire resistance of mature trees 



and reproduction, and in the requirements necessary for 



the establishment of seedlings, fires may in some cases 



be the controlling factor in determining which species 



may ultimately occupy a given site. J. V. Hoffman has 



indicated an area near the Oregon-California state line 

 where, due to light surface fires repeated at intervals 



