68 SOME INSECTS INJUEIOTJS TO FORESTS. 



Baltimore, Md., in December, 1908, spoke as follows : " I can agree 

 with Doctor Hopkins that the insects are far more important in 

 destroying our forests than fires." (Bruner, 1909, p. 53.) 



Insect-killed timber as fuel for fires.— It has often happened that 

 after insects have killed the timber over extensive areas the standing 

 and fallen dead trees furnished fuel for great forest fires which have 

 not only destroyed or charred the dead timber but killed the living 

 timber and reproduction and swept on into adjacent areas of healthy 

 timber. Indeed, abundant evidence has been found during recent in- 

 vestigations to indicate that some of the vast denuded areas in the 

 Eocky Mountains and other sections of the country are primarily due 

 to widespread devastation by insects, and that subsequent fires de- 

 stroyed the timber and prevented reproduction. (Hopkins, 1906a.) . 



It is also evident that a considerable percentage of dead timber, ^ 

 and especially that found in coniferous forest regions, which has gen- 

 erally been believed to have been fire-killed is a result of primary at- 

 tack by insects. This has been demonstrated in many cases by the 

 pitch-marked galleries of the destructive barkbeetles on the surface 

 of the wood of the old dead trees which had escaped subsequent fires. 



Fire-killed timber injured by insects. — It is true that a vast amount 

 of timber has been killed outright or has died as the direct result of 

 forest fires, but in almost every case observed insects have contributed 

 to a greater or less extent to the death of recently fire-injured trees 

 which might otherwise have recovered, and especially to the rapid 

 deterioration of the wood of a large percentage of the injured and 

 killed trees. It is evident that in some cases fire-scorched and fire- 

 killed timber has contributed to the multiplication of one or more of 

 the insect enemies destructive to living timber, and thus the injury 

 started by the fire may have resulted in a destructive outbreak of 

 beetles. However, it is evident that this has happened only when the 

 destructive beetle was already present, in abnormal numbers in the 

 forest surrounding the fire-swept area. Therefore, it is believed 

 that injuries by fire are not as a rule an important factor in contrib- 

 uting to subsequent depredations by barkbeetles. Such fires, how- 

 ever, contribute to the multiplication of the insects which depredate 

 on the bark and wood of dying and dead trees, so that in forested 

 areas where fires are frequent the damage to the wood of such trees 

 is more severe, and fewer injured trees recover on account of the 

 abundance of secondary barkbeetle enemies which do not, as a rule, 

 attack and kill living timber. 



Destruction of insects by fire. — There is another important feature 

 in the relation of insects and fire, in which the fire contributes to the 

 destruction of the principal barkbeetle enemies of the living timber. 

 This happens when the fire burns the timber while it is infested, thus 

 effectually destroying the broods of the insects. It is perfectly plain 

 that the dying and dead foliage of the beetle-infested trees and the 



