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ants, and wood-decaying fungi, all of which extend from year to year 

 their obscure yet destructive work. Nor does the trouble end here. 

 The dead trees and decaying wood of the living ones, as indicated on 

 previous pages, offer most favorable conditions for the starting and 

 spread of forest fires. It is therefore plain that in considering methods 

 of preventing depredations by insects those relating to the prevention 

 of forest fires are, under certain conditions, of special importance. 



In the nonreserved forests, where extensive timber operations are 

 carried on, the prevention of forest fires as a means of controlling 

 insect depredations is far less important than in the reserves. In fact 

 the debris in cut-over areas serves as attractive traps for the insects, 

 where they may be effectually destroyed, or their migration to healthy 

 timber prevented, by the almost inevitable conflagrations which follow 

 these cuttings. Therefore under such conditions it is not so much the 

 problem of prevention of fires as that of their control which should 

 receive attention, since if this debris can be burned at a time when the 

 conditions are least favorable for the fire to spread into the standing 

 timber the desired good, in the destruction of insects, would be attained 

 and the evil effects of the fires averted. On the other hand, every pos- 

 sible effort should be made to prevent outbreaks of fires in virgin and 

 reserved forested areas, not only to prevent the vast destruction by 

 fire alone, but as a precaution against destructive ravages by insects. 



Relation of insect enemies of trees to forest fires. — This is a subject on 

 which nothing appears to have been published, yet it requires only a 

 little observation in the Western forest to make it clear that the trees 

 which have been killed by insects furnish, in their fallen branches, 

 standing and fallen partly decayed trunks, and dry bark, a most favor- 

 able condition for the starting, rapid spread, and perpetuation of forest 

 fires. 



The relation of diseases of trees to insect enemies of forests. — It is 

 well known that forest trees weakened by disease contribute to the 

 multiplication of their insect enemies. It is also known that insects 

 will attack healthy trees, and that diseases of the bark and wood fol- 

 low as a result of such injuries. Therefore, in the investigations of 

 unhealthy conditions of forests it is often exceedingly difficult, with- 

 out some previous knowledge of the habits of the diseases and insects 

 found associated with them, to decide which is to blame for the pri- 

 mary injury. Our present knowledge of the subject, however, indi- 

 cates that as a rule unhealthy forest trees, like unhealthy animals, 

 present characteristic symptoms, which indicate quite clearly the pri- 

 mary cause of the trouble. The evidence I have been able to gather in 

 the forests of the East and Northwest makes it plain to me that, of the 

 two causes, while many small trees are killed by root diseases, the 

 unhealthy condition of the larger trees is more often due to primary 

 attacks by insects. Indeed- it appears that insects contribute more to 



