54 BULLETIN 275, U. S. DEPARTMENT OF AGRICULTURE. 



to show by means of one example the problems before us and the 

 various steps leading up to a working method for the future estab- 

 lishment of laws which may — or may not — confirm the conclusions 

 from this study, and to strongly advocate similar studies on a larger 

 scale. With this point plainly in view, but assuming that our con- 

 clusions are a step in the right direction, we may discuss their bear- 

 ing on the silvicultural problems that are before us. 



DECAY IN RELATION TO WOUNDS. 



In most cases, decay in white fir is caused by Echinodontium tinc- 

 torium. The mycelium never enters through the intact bark. Fire 

 wounds offer the most common way of entrance; hence, in the major- 

 ity of cases, decay starts in the butt; frost is less common than fire, 

 but favors the vertical spreading of typical decay. Localized and 

 superficial advance rot, frequently leaving enough merchantable 

 timber in the log to make it worth while handling except when 

 occurring in the upper part of the bole, is often connected with light- 

 ning. Other means of entrance, such as knots, wounds from falling 

 trees, and girdling by rodents are comparatively rare. 



These factors group themselves naturally into such as are uncon- 

 trollable and such as may be controlled directly or indirectly. The en- 

 trance of decay through knots, wounds from trees and limbs thrown 

 in heavy storms, or from excessive snowfall lies beyond our control. 

 Injury from mammals as a starting point of decay is very rare and 

 will become even more so with the decrease of the forest fauna. 



The other factors are more or less open to influence. Fire is dis- 

 tinctly a directly controllable factor. Lightning and frost are, of 

 course, not directly controllable. It is a fact, however, that both do 

 not occur to any damaging extent except in more or less well-defined 

 belts, and generally more heavily in foci inside of these belts. The 

 natural inference would be not to favor white fir in such belts when 

 possible. As a first step in this direction the establishment and map- 

 ping of frost belts, frost holes, lightning zones, and lightning foci 

 would be of particular value, which should not be confined to white 

 fir alone. Other forest trees are also more or less subject to injury 

 from both factors. The value of such maps should also make itself 

 felt in forest-fire control, for the proper distribution of protective 

 forces and improvements. 



FOREST REGULATION. 



CARE OF VIRGIN FORESTS. 



It has been heretofore pointed out that practically the only means 

 of siiviculturally influencing the national forests on a larger scale at 

 the disposal of the administration at the present time lies in the han- 

 dling of timber-sales areas. On all the vast forests outside of these 



