2 DEPARTMENT CIRCULAR 411, U. S. DEPT. OF AGRICULTURE 



recommends burning slash of western yellow pine for the control of 

 bark beetles. In England, Munro {8, p. 27), entomologist of the for- 

 estry commission, also recommends burning slash for control of bark 

 beetles. It is fully reahzed, however, that broad statements applying 

 indiscriminately to aU forested regions are out of the question; the 

 problem varies with each forest, region, and type. Not only must ^^ 



the species of tree and the character of the slash be considered but fc^ 



the various species of insects that may be involved must be taken 

 into account. 



It is recognized that, under special conditions, slash disposal or 

 seasonal timing of cutting operations is advantageous. Such cases 

 are referred to in the general text. 



Hopkins discusses this question in many of his papers. His 

 general conclusions are adequately supported by all the detailed 

 investigations so far conducted by the Division of Forest Insect In- 

 vestigations. As early as 1899 (^, p. 23) he called attention to the 

 wasteful methods of lumbering in the Northwest and the attractive 

 breeding places for forest insects provided by the scarred trunks and 

 the debris left on the ground. Ten years later, in his monograph, 

 {4, p. 25-26, 48), he suggests that the cutting of living timber for 

 commercial purposes may offer favorable conditions for the multiplica- 

 tion of some of the species, although in some cases it may serve as a 

 protection to hving timber, and suggests burning the slash after it 

 has attracted beetles away from the living trees. In one of his later 

 papers on forest entomology (5, p. 8) he broadly summarizes his 

 opinions as follows: 



Since the problem of slash disposal is on the program of this meeting and, 

 since it is pretty generally considered by foresters and some entomologists that 

 slash is an insect hazard to the living timber, I want to say that the results of 

 more than thirty years of observations and some detailed study of the problem 

 indicate that as a rule, it is not. As in all rules, there are, of course, exceptions 

 to this one. There are a few cases as related to certain types of forests, time of 

 year, and cases of sporadic cutting, where the slash is dangerous, not so much 

 from the insects that breed in the tops, logs, and stumps, as that it serves to 

 attract the tree-killing insects to the locality and from thus being concentrated 

 they attack and kill the living timber. Continued logging operations, after they 

 are once started within a given area, provide continuous breeding places for the 

 insects and their natural enemies and thus the slash serves as a protection to the 

 living timber. 



The entomologists of the Division of Forest Insect Investigations 

 feel that a paper setting forth what is now known about the entomo- 

 logical effect of slash would help to clear the situation and stimulate 

 more careful observation and compilation of further and needed data. 

 In this, as in most scientific problems, the last word can never be said, 

 and much investigative work is still needed to clear up many phases 

 of the slash problem. However, considerable work has already been 

 done, and certain tentative conclusions are presented in this circular. 



There are hundreds of species of insects which breed in the slash ^ 

 of forest trees, but few of these are capable of doing much injury to ^' 

 living trees. They attack the base, the trunk, the tops, the limbs, 

 or the twigs of mature standing trees; others emerge from slash and 

 attack seedlings, saplings, and poles. 



In addition to this, slash has a very strong attractive influence 

 which may result in bringing thousands of insects into the general 

 slash area with a resultant varying damage to living timber. 



