DISCUSSION AND CONCLUSIONS 



An average loss of 15.5 board feet per acre per year from attacks of DendroatoniAS 

 bark beetles underscored the endemic nature of these insect pests throughout the 

 duration of the study. At this low level of timber losses, the "bark beetle problem" 

 must certainly not have been of much concern to forest managers in western Montana 

 during the period from 1948 through 1968. Furthermore, the almost continuous endemic 

 infestations did not contribute as much as they might have to a meaningful test of 

 the Ponderosa Pine Risk Rating System here. This would have required a much greater 

 quantity of beetle-killed ponderosa pine trees than the sluggish infestations produced 

 for the study. 



Some questions, therefore, might well be asked. Will Dendroo tonus beetles, for 

 instance, ever be a problem in the management of mature ponderosa pine stands in western 

 Montana or, more broadly, throughout the northern Rocky Mountain States west of the 

 Continental Divide?^ And, if so, can the risk rating system help to alleviate it? 



To answer the first question, records of forest insect surveys in the northern 

 Rockies document past outbreaks of the western pine beetle and the mountain pine beetle 

 .in mature stands of ponderosa pine. True, these outbreaks have not produced such 

 devastating tree killing as have outbreaks of bark beetles in parts of the Pacific Coast 

 States where, in 1956 in one outbreak area, pine beetles killed an average of 208 board 

 feet of ponderosa pine per acre (Wickman and Eaton 1962) . Notwithstanding, the more 

 severe outbreaks of bark beetles in the northern Rockies have produced tree killing that 

 caused depletion of ponderosa pine stands and interfered with orderly forest management 

 planning and operations. Severe outbreaks of bark beetles will undoubtedly occur again 

 in the northern Rockies as long as there are stands of mature ponderosa pine trees and 

 as environmental conditions might change to encourage buildup of beetle populations to 

 epizootic levels. 



^The western pine beetle is not found east of the Continental Divide. East of the 

 Divide the mountain pine beetle becomes one of the primary tree-killing pests of the 

 Rocky Mountain form of ponderosa pine, Pinus ponderosa var. soopulorim Engelmann. The 

 ecology of this latter pest-host relationship is entirely distinct from that being 

 reported here. 



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