Mortality from the fir engraver soared in 1 995; 

 overstocking and drought are the underlying 



causes. Source: Cooperative Aerial Survey, Oregor) Departrr^ent of 

 Forestry and USDA Forest Service. 



math counties. The cause is a fir engraver 

 outbreak after several years of below-aver- 

 age precipitation. Much of the mortality was 

 in overstocked stands at elevations below 

 6,000 feet. Before fire-suppression pro- 

 grams, most of these sites 

 were dominated by ponder- 

 osa pine stands. A similar 

 pattern of white fir mortality 

 is affecting areas of northern 

 California. Because few of 

 the dead trees have been sal- 

 vaged, the potential for cata- 

 strophic fire in Oregon re- 

 mains high. 



The Douglas-fir beetle 

 killed thousands of trees in 

 recent years, especially in 

 areas where the host trees 

 sustained heavy budworm 

 defoliation. After the spruce 

 budworm outbreak, these 

 bark beetles have attacked 

 and killed many of the trees 

 weakened by several years of 

 defoliation and drought. 

 Characteristically, Douglas- 



Armillaria root disease is the 

 key disturbance agent in many 

 mixed conifer stands. Trees 

 weakened by soil compaction, 

 drought, and overcrowding are 

 very susceptible to armillaria. 



fir beetles select the largest trees in the stand 

 and thus have profound effects on stand 

 structure. These effects have been most 

 notable in recent years on the Sisters Ranger 

 District (Deschutes National Forest), the 

 Warm Springs Indian Reservation in the 

 eastern Cascades, and the Malheur, 

 Umatilla, and Wallowa-Whitman National 

 Forests in the Blue Mountains. 



Shifts in tree species cause increased 

 root disease — Root diseases cause subtle, 

 but persistent growth loss and mortality in 

 mixed conifer stands. When disease pock- 

 ets are small and scattered, they often in- 

 crease the structural diversity and benefit 

 wildlife and understory plants. Large root- 

 disease pockets in areas designated for tim- 

 ber management cause significant economic 

 loss and increase fuel loading. 



Root disease has increased in mixed co- 

 nifer stands as host species have increased. 

 Fire exclusion has resulted in less pine and 

 larch, species more resistant to root dis- 

 eases, and greater numbers of the more sus- 

 ceptible Douglas-fir and true fir. Partial cut- 

 ting of mature trees in root disease areas, a 

 common management practice, can intensify 

 root disease problems. Root 

 disease fungi colonize the 

 roots and stumps of cut trees 

 and then spread to live trees. 

 Partial cutting also results in 

 natural regeneration of sus- 

 ceptible species in the dis- 

 eased area. Disease centers 

 will remain a problem in 

 managed mixed conifer 

 stands until the use of fire or 

 other silvicultural treat- 

 ments promote the regenera- 

 tion of resistant serai species 

 such as pine and larch. In- 

 creases in the proportion of 

 true fir and Douglas-fir in 

 mixed conifer stands have 

 led to increases in armillaria 

 and annosus root diseases 

 and laminated root rot. 



Oregon — 36 



