100 



> 



5 8 

 u> 

 c 



US 



a 

 c 



K 60 



I 



1 



« 40 



» 20 

 Cl 



Lodgepole pine data 1891, 1992 



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



Percent Basal Circumference Killed 



Figure 8 — Relationship of pine engraver infes- 

 tation to basal fire injury of lodgepole pine. 



Total 



Lodgepole pine mortality 1991 versus 1992 



Weighted Regression Analysis 



1991 



Y = 14.0 + 0.32** 

 R"2 = 0.93 



a 1991 V1992 



1992 

 V= 27.2 + 0.21** 

 fl**2 = 0.80 



20 40 60 



Percent Basal Fire Injury 



Figure 10 — Relationship of insect infestation 

 to basal fire injury of lodgepole pine, 1991 

 versus 1992. 



Mountain pine beetle infested only a small number 

 of lodgepole pine and did not show much preference 

 for any fire-injury class. Infestation ranged between 

 0.3 percent of the trees in the 61 to 80 percent basal 

 injury class to 1.2 percent of the uninjured tree class 

 (fig. 11), which is consistent with previous measure- 

 ments in the Greater Yellowstone Area (Amman 

 and Ryan 1991) and other studies (Blackman 1931; 

 Hopkins 1905). Mountain pine beetle appears not 

 to respond to trees stressed by fire or drought, since 

 both were present in the Greater Yellowstone Area 

 during this study. An alternative hypothesis is that 

 beetles respond to stressed trees but are unable to 

 build up populations in them. Schmitz (1988) observed 

 mountain pine beetle infesting diseased lodgepole 

 pine when beetle populations were at an endemic 



level, but brood production was low which prevented 

 buildup of the beetle population. Not until mountain 

 pine beetles infest better quality lodgepole pine (those 

 growing faster and having thicker phloem, which is 

 the food of developing larvae) does the population 

 build to a potential outbreak. 



Our sample of Douglas-fir (1991 and 1992 surveys 

 combined) showed that 41.6 percent of all fire-injured 

 trees were infested by insects. Infestation ranged 

 from a low of 18.4 percent of uninjured trees to a high 

 of 79.7 percent of trees having 81 to 100 percent of 

 the basal circumference girdled by fire (fig. 12). The 

 Douglas-fir beetle accounted for the most infestation, 

 ranging between 16.3 percent of the uninjured trees 

 to 47.0 percent of trees having 81 to 100 percent basal 



Lodgepole pine mortality 1991, 1992 



Weighted Regression Analysis 



V= 18.8 + 0.281*X 

 fl**2 = 0.94 



40 60 



Percent Basal Fire Injury 



Figure 9 — Relationship of insect infestation 

 to basal fire injury of lodgepole pine. 



, 100 



80 



60 



40 



20 



Lodgepole pine data 1991, 1992 



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



Percent Basal Circumference Killed 



Total 



Figure 11 — Relationship of mountain pine beetle 

 infestation to basal fire injury of lodgepole pine, 

 1991 and 1992. 



6 



