Bark Beetle and Wood Borer 

 Infestation in the Greater 

 Yellowstone Area During Four 

 Postfire Years 



Lynn A. Rasmussen 

 Gene D. Amman 

 James C. Vandygriff 

 Robert D. Oakes 

 A. Steven Munson 

 Kenneth E. Gibson 



Survival of conifers following fire depends on the 

 type and degree of injuries, initial tree vigor, and the 

 postfire environment, which includes the influence 

 of insects, diseases, and weather. As fire injury in- 

 creases, the probability of death due to one or more 

 of these causes also increases. 



Bark beetles of the family Scolytidae and wood 

 borers of the families Buprestidae and Cerambycidae 

 are frequently associated with tree mortality following 

 fire. In the absence of significant bole or root injuries, 

 the probability of attack by primary bark beetles (those 

 attracted to healthy trees) is low when fight defolia- 

 tion by fire occurs and the probability usually declines 

 further with complete defoliation (Furniss 1965; Miller 

 and Keen 1960; Mitchell and Martin 1980; Wagener 

 1961). Secondary bark beetles (those commonly at- 

 tracted to severely weakened or recently killed trees) 

 and wood borers are drawn to burned trees, but their 

 contribution to mortality, while thought to be minor 

 (Mitchell and Martin 1980) is largely unknown. 



Observations on permanent plots that were estab- 

 lished in the Greater Yellowstone Area in 1989 and 

 1990 showed increased susceptibility of insect infes- 

 tation with increased fire injury for most tree species. 

 However, trees that were completely defoliated by 

 canopy fires that also resulted in complete burning 

 or severe scorching of the inner bark, especially in 

 thin-barked trees, were no longer suitable for bark 

 beetle infestation (Amman 1991; Amman and Ryan 

 1991). Insect contribution to tree mortality is some- 

 times difficult to determine because of nonobvious 

 bole and root injuries by fire. These injuries result in 

 inaccurate mortality predictions from existing models 

 based on crown scorch alone (Ryan and Amman 1994). 



Because of the small number of permanent plots 

 used to follow tree mortality pertaining to fire injury 



in the Greater Yellowstone Area, surveys for insect 

 activity were conducted to obtain a larger sample on 

 which to investigate interactions between insects and 

 fire-injured trees. The objectives of our study were to 

 determine delayed tree mortality attributed to fire 

 injury and bark beetles and the effects on mosaics of 

 fire-killed and green (live) trees, the relationship be- 

 tween fire injury and subsequent infestation by bark 

 beetles and wood borers, and the buildup of bark 

 beetles in fire-injured trees and subsequent infesta- 

 tion of uninjured trees. 



Methods 



Extensive surveys for bark beetle activity were con- 

 ducted in 1991, 1992, and 1993. The surveys followed 

 roads in Yellowstone Park and Rockefeller Memorial 

 Parkway (fig. 1); limited resources prevented a more 

 complete survey that would have included back coun- 

 try and areas closer to roads. The plot locations were 

 randomized by selecting random distances to be driven 

 down a road, flipping a coin to determine whether 

 plot establishment would be on the left or right side 

 of the road, and selecting at random the distance the 

 plot would be located from the road (40 to 100 m). 



To be used in our study, the plot must have con- 

 tained some trees with green foliage. Canopy fires that 

 caused complete defoliation usually resulted in com- 

 plete burning or severe scorching of the inner bark, 

 especially in thin-barked species. Trees with this type 

 of injury were no longer suitable for bark beetle infes- 

 tation (Amman 1991). Therefore, our sampling focused 

 on areas where canopy fires had not occurred and on 

 adjacent unburned forest. If the trees in the plot were 

 dead or faded, the location was moved to the next 



