382 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



These studies have revealed that the risk of being killed by western pine 

 beetles is distinctly greater for trees of certain types than it is for other trees 

 in the same stand. In general, the trees more susceptible to attack are the 

 weaker, less vigorous individuals and, to a certain degree, those more advanced 

 in age. The problem, therefore, is one of recognizing the combination of char- 

 acters which indicates susceptibility. 



Silvicultural management of our ponderosa pine forests should eventually 

 lead to the solution of the present pine beetle problems. Although forest manage- 

 ment may not eliminate all future bark beetle troubles, it is at least a step in 

 the right direction of improving the chances of ponderosa pine stands to escape 

 such injury. 



The practicability of Keen's scheme was quickly recognized, and 

 actual marking of timber sales by this classification was carried out 

 in Oregon and Washington and adaptations of the system were used 

 by foresters in the Southwest and in the Rocky Mountain regions. 

 The results were good and led to further study and refinement of the 

 characteristics of "bug trees." 



About this time thought along these lines had crystallized suffic- 

 iently to demand further experimental plots for testing the possibili- 

 ties of marking beetle-susceptible trees. In 1936, on the Blacks 

 Mountain experimental area, the California Forest Experiment Sta- 

 tion set aside certain areas for use of the Berkeley laboratory of the 

 Bureau of Entomology and Plant Quarantine, and Bongberg and 

 Salman marked the "bug trees" on the basis of their ideas of the 

 characteristics that indicate susceptibility. After 4 years the results 

 of this work have been highly satisfactory and are being applied by 

 private interests and the United States Forest Service in Oregon and 

 California. Salman and Bongberg (1941) have shown that on these 

 experimental areas they were able to mark and remove before attack 

 85 percent of the trees that would have been destroyed by bark beetles 

 from comparison with the losses on adjacent areas. 



Thus after many years of direct-control efforts against the western 

 pine bettle and the testing of several methods for marking and cut- 

 ting of ponderosa pine on Federal and private lands in an effort 

 to obtain sustained yield, we are now anticipating nature's ruthless 

 but effective method — selection by climate and beetles. For many 

 years this selection system has been going on before our eyes but 

 only recently have we seen it — no doubt, we still see only a part of 

 it. It is still too early to predict the success of this method, aptly 

 phrased "beating the bettle to it." Theoretically it looks good. If 

 we remove the susceptible trees before the beetle broods develop 

 in them, it seems reasonable to believe that beetles cannot increase in 

 numbers and become aggressive to the point of killing nonsusceptible 

 trees. In practice, success will depend on several considerations. 

 Logging methods and terrain, as well as the lumber demand, will 



