r 40 



20 



Douglas-fir data 1991, 1B92 



.11 



1-20 21-40 41-60 61-80 81-100 Total 

 Percent Basal Circumference Killed 



Figure 12 — Percent insect infestation of 

 Douglas-fir by fire-injury class. 



Douglas-fir mortality 1991 , 1992 



Weighted Regression Analysis 



V- 17.5 + 0.53*X 

 R"2 - 0.69 



Percent Basal Firs injury 



Figure 14 — Relationship of insect infestation 

 to basal fire injury of Douglas-fir. 



100 



injury (fig. 13). Pseudohylesinus nebulosus was the 

 second most common bark beetle infesting Douglas- 

 fir, followed by the wood borers. Regression relation- 

 ships between basal girdling by fire and infestation 

 are shown in figure 14. 



Our sample of Engelmann spruce for 1991 and 1992 

 combined show that 28.7 percent of trees across all 

 injury classes were infested by insects. Infestation 

 ranged from 10.1 percent of the uninjured trees to 

 53.6 percent of trees having 41 to 60 percent of their 

 basal circumference killed by fire (fig. 15). Spruce 

 beetle accounted for almost one-half of the infested 

 trees (13.9 percent). Infestation by spruce beetle ranged 

 between 5.8 percent of uninjured trees to 39.3 per- 

 cent of trees having 41 to 60 percent basal girdling; 

 the infestation is usually limited to the lower 20 ft of 

 the trunk (Schmid 1976). Therefore, bark scorching 

 in the injury classes exceeding 60 percent girdling of 



the basal circumference may deter beetles from in- 

 festing such heavily injured trees (fig. 16). 



Our samples of subalpine fir (134 trees) and white- 

 bark pine (144 trees) were too small to draw meaning- 

 ful conclusions about insect response to different fire 

 injury levels. However, it does appear that insects, 

 mostly wood borers, prefer the more severely injured 

 subalpine fir (fig. 17). 



No strong relationship between fire injury and in- 

 festation existed in the whitebark pine data (fig. 18). 



Buildup of Insects in Fire-Injured Trees 



The insect buildup in fire-injured trees and subse- 

 quent increase in infestation of trees uninjured by 

 fire was studied by relating infestation to the year 

 of occurrence. Dating infestation in 1989 and 1990 

 depended on foliage coloration; 1991 and 1992 were 



Douglas-fir data 1991, 1992 



1-20 21-40 41-60 61-80 81-100 

 Percent Basal Circumference Killed 



total 



Figure 13 — Percent Douglas-fir beetle infestation of 

 Douglas-fir by fire-injury class. 



1-20 21-40 41-60 61-80 81-100 

 Percent Basal Circumference Killed 



Figure 15 — Relationship of all insect infestation 

 to basal fire injury of Engelmann spruce. 



Total 



7 



