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



self. Fires as well as insects and disease outbreaks developed, spread 

 destruction, and ran their course. The whole process was very waste- 

 ful but seldom resulted in the permanent destruction of the forests 

 OA^er 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 increase 

 in values came the necessity for better protection and management. 

 The first step in stopping Nature's wasteful processes was the con- 

 trol of forest fires. Later, with more intensive forest management 

 and the develoj^ment of control methods, attention was turned to the 

 prevention of losses from forest insects and disease. As time goes 

 on and forest values increase, more and more attention will be given 

 to preventing or controlling forest-insect damage, and a greater re- 

 finement in methods will be.come 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 predacious 

 forms, as well as between the insects and their food supply, so as to 

 prevent the development of destructive insect outbreaks. This ob- 

 jective will be attained more fully in the future through silvicultural 

 practices applied to growing stands whereby unfavorable conditions 

 for the development of insects are maintained and a greater resist- 

 ance of the stand to insect attacks is developed. This may involve 

 such measures as prompt disposal of slash and correction of other 

 insect -breeding conditions, the regulation of stand density and com- 

 position, the regulation of environmental factors through drainage 

 or other methods, and the selection of insect -resist ant varieties and 

 species of trees. 



When preventive methods fail to avert insect outbreaks, direct con- 

 trol measures must be considered. The total elimination of a forest 

 insect is quite impractical, but fortunately this need not be attempted. 

 Instead, the objective of direct control is the restoration of the natural 

 balance in which the destructive insects are not greatly out of propor- 

 tion to their natural enemies. In such proportions the destructive 

 species are relatively harmless, and the damage they do is insig- 

 nificant. 



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

 to control all insect outbreaks. Much of the insect damage to forest 

 trees of low value will have to be allowed to run its course, for if a 

 policy of combating all threatening insect outbreaks were adopted 

 the cost would be enormous and in many cases would exceed the 

 damage probable if Nature were allowed to control the epidemic in 

 her own way. The older forests, as they stand today, are ripe and 

 an easy prey to bark-beetle attack, and if we are not prepared to 

 utilize such timber and are willing to wait for Nature to replace any 

 losses by the slow process of growing a new crop of trees, no further 

 consideration need be given to control. On the other hand, in the 

 many cases in which timber is in demand and satisfactory control 

 measures are available, failure to take the necessary protective meas- 

 ures should be viewed in the same light as failure to control forest 

 fires. 



I 



