system, such trees in northeastern California and eastern Oregon are rated as being 

 either highly or very highly susceptible to lethal infestation by the pine beetle. Ex- 

 tensive tests made as late as 1959 have confirmed the capability of sanitation-salvage 

 cuttings to minimize such destructive depletion of the ponderosa pine resource as oc- 

 curred during the period from 1940 to 1959 in northeastern California and eastern Oregon 

 (Keen and Miller 1960; Wickman and Eaton 1962). 



Despite the apparent success of sanitation-salvage cuttings to control the pine 

 beetle in the Pacific Coast States, several inherent differences in the ecology of 

 ponderosa pine forests and the western pine beetle in the northern Rockies raised 

 questions about use of such cuttings to achieve similar insect control benefits in 

 this mountain region. Furthermore, ponderosa pine stands in the northern Rocky Moun- 

 tains during the 1940' s were experiencing environments favoring good tree vigor and 

 growth. Almost nothing was known of the possible response of consequent endemic pine 

 beetle populations to sanitation-salvage cuttings that might be applied as a control 

 measure under these conditions. 



However, this concern about the effectiveness of the cuttings was largely academic 

 because information was not available on the adaptability in the northern Rockies of 

 the Ponderosa Pine Risk Rating System upon which the cuttings relied. The rating sys- 

 tem's effectiveness in identifying beetle susceptible trees to be removed from pine 

 stands by the cuttings had to be determined before any tests of the cuttings as a beetle 

 control measure could be undertaken in this region. To obtain this information, a study 

 of the effectiveness of the risk rating system was undertaken in western Montana in 1948 

 by the Coeur d' Alene (Idaho) Forest Insect Laboratory of the former Bureau of Entomol- 

 ogy and Plant Quarantine. The study was continued by the Intermountain Station until 

 1969. 



In the study, we sought to determine (1) whether the western pine beetle has an 

 affinity for attacking ponderosa pine trees classified as high risk, or beetle suscepti- 

 ble, using this rating system, (2) whether such attacks might be diverted by attractions 

 created in low risk trees as a result of prior infestations in these trees by the moun- 

 tain pine beetle, Dendpoatonus pondevosae Hopkins, or the pine engraver, Ips pini Say 

 (Coleoptera: Scolytidae), or (3) whether the western pine beetle constituted a serious 

 threat to mature ponderosa pine stands in the northern Rockies. 



Endemic populations of the western pine beetle killed only minimal amounts of 

 ponderosa pine timber during the 20-year span of the study. This and nearby harvest 

 cuttings that made ecological islands of some of the study plots argued against further 

 extensions of the study. Consequently, the study was terminated upon completion of tree 

 mortality measurements of the 1968 beetle population. 



3 



