INSECTS AND FOREST MANAGEMENT — CRAIGHEAD 379 



numbers is conditioned by physiological changes in the trees brought about by 

 deficiency in rainfall or opening of the stand which allows greater desiccation. 



Person (1928*) was the first to give this predilection of the beetle for 

 certain trees a definite terminology, using "tree susceptibility" and 

 "beetle selectivity." His work showed that 



• * * tree selection, as used in this paper, is not Intended to mean a con- 

 scious selection of certain trees by the insects, but rather that trees having certain 

 characteristics are more apt to be killed by the western pine beetle than trees 

 which do not have them. 



The preference of the western pine beetle for the slow-growing trees varies 

 with the area and the status of the infestation, being more marked under endemic 

 or increasing conditions than under decreasing epidemic conditions. 



The slow-growing trees, which are of least value for producing wood, are the 

 trees most likely to be killed by the western pine beetle. If these trees can be taken 

 out in the earliest cutting of timber the condition of cut-over areas will be 

 materially improved from the standpoint of insect damage and of subsequent 

 growth. 



In a later paper (1931) Person states: 



Any increase in our knowledge of how the western pine beetle selects the trees 

 which it kills will make it possible to reduce this loss by leaving on our cut-over 

 areas only such trees as will have the best chance of surviving until the next cut. 



A greater knowledge of tree attractiveness and stand susceptibility will 

 make it possible to determine the probability of insect loss when the logging 

 plan is first drawn up, before the insect loss occurs, thus obviating the necessity 

 of later changes, which are usually costly. 



Dunning (1928) , in presenting a tree classification for western yellow 

 pine, recognized the importance of bark beetles as a mortality factor. 

 To quote: "The greatest single cause of mortality was bark beetles 

 {Dendroctonus) which killed 61, or 35 percent, of the 172 trees and 

 accounted for 50 percent of the basal-area loss." He also comments 

 on the possibility of using in management, the selectivity shown by 

 these beetles, stating that "The elimination of susceptible trees in cut- 

 ting would doubtless lessen endemic insect damage, the most important 

 cause of loss on cut-over areas." 



In presenting an appraisal of control, Craighead, Miller, Keen, and 

 Evenden (1931) point out that the results of control work against the 

 western pine beetle have "not been spectacular or outstanding * * * 

 and the benefits only temporary. * * * Such (control) work may 

 be combined with selective logging to remove susceptible trees and 

 produce better growth conditions in order to give permanent pro- 

 tection for long periods." 



Further developments with this idea were reported in 1933 (Senate 

 Document 12) following actual experimental tests in removmg 

 beetle-susceptible trees (fig. 1) : 



Much progress has been made in recent years toward establishing sustained 

 yield on both Federal and private timberlands in the ponderosa pine type of 

 California and Oregon. The management of these stands is based on an initial 



