12 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



the stripped trees dries out quickly and becomes highly inflam- 

 mable. A flash of lightning, or a carelessly handled match or ciga- 

 rette sets off the mass, causing a widespread conflagration almost 

 impossible to control. Heavy defoliations in Douglas-fir and hem- 

 lock stands and epidemics of the mountain pine beetle in lodgepole 

 pine have put the forest in such a condition that, more often than 

 not, forest fires have followed. The increased fire hazard is an 

 added reason why forest-insect outbreaks should be controlled 

 wherever possible. 



RELATION OF INSECTS TO 

 FOREST MANAGEMENT 



Under virgin-forest conditions no checks were placed on the ac- 

 tivities of destructive agents other than those imposed by Nature 

 herself. Fires, as well as insects and disease outbreaks, developed, 

 spread destruction, and ran their course. The whole process was 

 very wasteful but seldom resulted in the permanent destruction 

 of the forests over any large areas. Natural checks were imposed 

 and the processes of regeneration were brought into play. 



With the development of the country and a corresponding in- 

 crease in values came the necessity for better protection and man- 

 agement. The first step in stopping Nature's wasteful processes 

 was the control of forest fires. Later, with more intensive forest 

 management and the development of control methods, attention 

 was turned to the prevention of losses from forest insects and 

 disease. As forest values increase, more and more attention will 

 be given to preventing or controlling forest-insect damage, and a 

 greater refinement in methods will become economically justifiable. 



In a managed forest the first objective of forest-insect control is 

 to so regulate conditions as to maintain a natural balance between 

 the insect population that is destructive and the beneficial preda- 

 cious forms, as well as between the insects and their food supply, 

 to prevent the development of destructive insect outbreaks. This 

 objective will be attained more fully in the future through silvi- 

 cultural practices applied to growing stands whereby unfavorable 

 conditions for the development of insects are maintained and a 

 greater resistance of the stand to insect attacks is developed. This 

 may involve such measures as prompt disposal of slash and cor- 

 rection of other insect-breeding conditions, the regulation of stand 

 density and composition, the regulation of environmental factors 

 through drainage or other methods, and the selection of insect- 

 resistant varieties and species of trees. 



When preventive methods fail to avert insect outbreaks, direct 

 control measures must be considered. The total elimination of a 

 forest insect is impractical, but fortunately this need not be at- 

 tempted. Instead, the objective of direct control is the restoration 

 of the natural balance in which the destructive insects are not 

 greatly out of proportion to their natural enemies. In such pro- 

 portions the destructive species are relatively harmless, and the 

 damage they do is insignificant. 



In view of present forest values it is hardly practical to attempt 



