THE RELATION OF IXSECTS TO SLASH DISPOSAL H 



the extensive and continuous character of the logging operations. 

 Recently, however, reports from the British Columbia Forest Service 

 indicate heavy killing of Douglas fir adjacent to certain logging 

 operations on the coast of British Columbia. 



In the northern Rocky Mountain region conditions are somewhat 

 different. The Douglas fir beetle {Dendroctonus pseudotsugae Hopk.) 

 is apparently much more aggressive in these less humid sections. 

 In receat 3'ears it has been causing considerable damage, and coming 

 more and more to be considered a serious insect. Evenden believes 

 that several local outbreaks under his observation are clearly attrib- 

 utable to slash which has resulted from logging operations, con- 

 struction of rustic buildings, spruce-budworm defoliation (resulting 

 in the death of many trees), or windfalls. 



Two small bark beetles, Scolytus unispinosus Lee, and Pseudosy- 

 lesinus nehulosus (Lee.,) occasionalh' multiph' in slash, and when no 

 more material is available they cause damage to reproduction and to 

 young trees. 



The question of the destruction of Douglas fir by insects needs 

 much more thorough study and more systematic observations before 

 any conclusions can be ventured. 



CONCLUSIONS 



The outstanding conclusions which have been reached to date in 

 regard to the entomological aspect of slash disposal are given here. 



Asfar as is now known, pine, spruce, and Douglas fir are the only 

 species of timber to which insects associated with slash are of any 

 important economic significance. 



Comparatively few species of insects are capable of adapting 

 themselves to breeding in slash and killing living trees. 



The great majorit}' of the important tree-killing insects which 

 attack slash breed largely in the cull logs and butts. It follows that the 

 present methods of brush burning can have little influence on their 

 control. 



Where logging operations are continuous, and a constant supply of 

 slash is provided, the potential danger from insects need cause no 

 concern. 



Slash attracts from the surrounding forests insects which often 

 concentrate in standing timber in the vicinity of the cutting. No 

 method of slash disposal will avoid this effect. 



In special cases where the value of the surrounding timber is 

 greatly enhanced, either from an aesthetic standpoint as a building 

 site or for scientific purposes such as experimental thinnings in sample 

 plots, extreme caution should be exercised in felling green timber. 

 In such cases the attraction of the felled timber for insects is more 

 important than its service as a breeding ground, and all such work 

 should be done in the fall or winter, at least two months before the 

 growing season. 



A large number of insects of secondary importance breed in the 

 twigs, limbs, and trunks of fallen trees, and sometimes become so 

 numerous as to kill reproduction, pole stands, and occasionally even 

 mature trees in the vicinity. Such outbreaks are, however, sporadic 

 in nature and of short duration, and, under present economic con- 

 ditions, do not warrant special methods of slash disposal. 



