100 



80 



20 











Subalplne fir 



{Abies lasiocarpa) 

























Green Fire Insect Unknown mortality 



Stand Composition (present) 



Figure 5 — Alive (green) and dead subalpine fir 

 by cause of mortality. 



20 







Whitebark pine 



(Pinus albicaulis) 



























Green 



Fire Insect Unknown mortality 



Stand Composition (present) 



Figure 6 — Alive (green) and dead whitebark 

 pine by cause of mortality. 



to fire injury (50 percent), with insects accounting 

 for only 7.5 percent and unidentified causes 5.2 per- 

 cent (fig. 5). Subalpine fir is the most sensitive to fire 

 injury of the tree species in this study (Ryan and 

 Amman 1994). Most insect-caused mortality of sub- 

 alpine fir was caused by wood borers in the families 

 Cerambycidae and Buprestidae. 



Whitebark pine also appears sensitive to fire in- 

 jury in the fire types that occurred in the Greater 

 Yellowstone Area in 1988, with only 36.1 percent of 

 the 144 trees in our sample surviving. Mortality in 

 trees was attributed to the following causes: 59.7 per- 

 cent to fire injury, 2.8 percent to insects, and 1.4 per- 

 cent to unidentified causes (fig. 6). Whitebark pine 

 was usually killed by mountain pine beetle and pine 

 engraver. 



Delayed mortality from fire injury and insects 

 ranged between 41 and 64 percent in the tree species 

 represented in this study. This mortality resulted in 

 drastic changes in dead and green tree mosaics that 

 were observed immediately following the 1988 fires. 

 Losses to fire injury could be determined shortly af- 

 ter the fires by examining trees for complete basal 

 girdling; however, predicting losses to insect infesta- 

 tion was more difficult. Observations in the next sec- 

 tion provide the basis for making such predictions. 



Infestation in Relation to Fire Injury 



Insect infestation was positively related to the 

 percent of the basal circumference killed by fire in 

 Douglas-fir, lodgepole pine, and Engelmann spruce. 

 Meaningful relationships were not established for 

 subalpine fir and whitebark pine because of the small 

 amount in our sample. 



Our sample of lodgepole pine showed that a total of 

 43.9 percent of all fire-injured trees were infested by 



insects. Infestation ranged from a low of 21.7 percent 

 in lodgepole with no injury to a high of 66.6 percent 

 in trees with 81 to 100 percent basal girdling by fire 

 (fig. 7). The pine engraver accounted for the most 

 lodgepole pine infestation, ranging from 16.6 percent 

 of trees in the uninjured class to 44.8 percent of trees 

 in the 81 to 100 percent basal injury class (fig. 8). 

 Twig beetles (Pityphthorous and Pityogenes) were 

 the next most common, with the wood borers (Cer- 

 ambycidae and Buprestidae) infesting a few trees. 

 Regressions showing the relationships of infestation 

 to fire injury are given in figure 9. Infestation in- 

 creased in all injury classes in 1992 (fig. 10). The 

 increase in the uninjured class indicates a possible 

 jump in pine engraver populations within fire-injured 

 trees in previous years resulting in the increase in 

 infestation of uninjured trees. 



100 

 fi 80 



Lodgepole pine data 1991, 1992 

























h 















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



Percent Basal Circumference Killed 



Figure 7 — Percent insect infestation of lodgepole 

 pine by fire-injury class. 



5 



