turbed areas, where 38 to 51% of the larch in 

 a stand might be infected. Where larch stands 

 are managed, the removal of badly infected 

 trees can reduce the amount of infection and 

 increase vigor of the whole stand. Dwarf 

 mistletoe is also common in Douglas-fir, pon- 

 derosa pine, and lodgepole pine. In pine, the 

 most severe mistletoe infections tend to be in 

 stands with a high proportion of pine and in- 

 frequent-fire histories. 



Mixed Conifers 

 Western spruce budworm population col- 

 lapses in mixed conifer stands — The most 

 significant and persistent defoliating insect in 

 eastern Oregon has been the western spruce 

 budworm. Between 1980 and 1992, more than 

 400,000 acres of host type in central Oregon 

 and more than four million acres in the Blue 

 Mountains were affected by the budworm. This 

 outbreak coincided with a drought that af- 

 fected most of eastern Oregon. Douglas-firs, 

 grand firs, and white firs were repeatedly de- 

 foliated at various intensities on the Ochoco, 

 Deschutes, Wallowa- Whitman, Umatilla, and 

 Malheur National Forests. Some of the defo- 

 liation effects included topkill, tree mortality, 

 reduced growth, elimination of cone crops, and 



reduced resistance to other agents of mortal- 

 ity such as root diseases and bark beetles. In 

 the most extreme cases (where the susceptible 

 host type was most abundant), around 80% 

 of the trees died. Spruce budworm popula- 

 tions collapsed region wide in 1992, and very 

 little current defoliation is evident in this part 

 of Oregon. 



Bark beetles benefiting from crowding 

 and drought — Several bark beetles have been 

 important in eastern Oregon mixed conifer for- 

 ests in the past decade: fir engraver, Douglas- 

 fir beetle, and western pine beetle. These in- 

 sects are opportunistic and usually benefit 

 from stress on the host tree resulting from 

 crowding, disease, defoliation, or drought. Old- 

 growth set- aside stands, where management 

 activities are restricted, suffered high tree 

 mortality. An unprecedented amount of fuels 

 from insect-killed trees has accumulated dur- 

 ing the last decade. The abundance of over- 

 stocked, low vigor, mixed conifer stands in 

 eastern Oregon makes a repeat of the massive 

 tree mortality in the 1980s an eventual cer- 

 tainty. 



One of the most conspicuous vegetation 

 changes in southeastern Oregon was the 

 massive white fir mortality in Lake and Kla- 



Western spruce budworm defoliation was 

 apparent on almost all lands where the host 

 species grew between 1 980 and 1 992. 



Source: Cooperative Aerial Survey, Oregon Deportment of Forestry and 

 USDA Forest Service. 



Western Spruce Budworm 



9 rt t 



re O 

 [O 2 3 



a> o 

 "=> = 

 E 2 



^ElL 



Year 



The number of acres affected by western spruce 

 budworm in eastern Oregon peaked in 1 986. 



Source: Cooperative Aerial Survey, Oregon Department of Forestry and 

 USDA Forest Service. 



Oregon — 35 



