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



Trees that have been felled by wmcl or snow and those struck by 

 lightning furnish favorable breeding places for a great many destruc- 

 tive bark and wood borers. Such material is probably the natural 

 habitat for many species that at times become excessively abundant 

 and attack living trees. Many severe bark-beetle epidemics are 

 known to have originated in areas of wind-blown timber. 



SLASH 



The debris left from the cutting of trees in the forest is a suitable 

 and attractive breeding ground for a great many forest insects, some 

 beneficial and some harmful (^7, 67, 8Ji). When slash is freshly 

 produced, the dying inner bark is attractive to many species of bark 

 beetles that are commonly found breeding in standing trees. Usually 

 these bark beetles select in the slash or stumps the type and size in 

 which they normally breed. Thus the limb- and twig- feeding bark 

 beetles go into the brush and smaller pieces of slash, trunk-breed- 

 ing bark beetles go into the cull logs and butts, and those that nor- 

 mally work at the base of the tree attack the stumps. The abundance 

 of the progeny depends a great deal upon the moisture and temper- 

 ature conditions within the slash and the requirements of the differ- 

 ent species of beetles. The red turpentine beetle, which breeds readily 

 in pine stumps, frequently develops in such numbers as to do serious 

 injury to adjacent forest trees. The trunk-breeding pine beetles 

 rarely find suitable conditions in the cull logs and butts, and the 

 progeny which they produce under such circumstances seldom cause 

 any trouble in neighboring forests or to the reserve stand, especially 

 where logging operations are continuous. The engraver and twig 

 beetles, which breed in the smaller pieces of slash, frequently emerge 

 in such enormous numbers as to kill patches of young trees and 

 sometimes the tops of older trees. 



The wood-boring species that breed in slash must be considered 

 generally beneficial, in that they help to decompose the wood and 

 reduce the slash with its accompanying fire hazard. 



They may become injurious, however, and in order to avoid or reduce 

 a possible menace from slash-breeding insects special considerations 

 in slash disposal are frequently necessary. When a logging operation 

 is continuous, and a fresh supply of slash is furnished throughout 

 the flight period, the emerging progeny is repeatedly absorbed in the 

 slash and in the logs removed to the mill, and no special precautions 

 need be taken. But if a cutting operation ceases or is intermittent, 

 as in the case of road and power-line development, then some damage 

 from slash-breeding insects may be expected and should be avoided 

 if possible. Burning the slash is beneficial provided the large limbs, 

 cull logs, and stumps are included and the burning done before the 

 insects emerge. In many cases this would mean that the burning 

 would have to be done in the middle of summer or early in fall, and 

 this would not be safe from the standpoint of fire hazard. Spreading 

 the slash so as to receive the direct rays of the sun is effective in 

 disposing of a high percentage of the insects in the more southern 

 latitudes where high temperatures can be attained in and under the 

 bark in this way. 



