and other land managers to recognize and cor- 

 rect tree hazards. Corrective measures may 

 include tree removal, tree replacement, or 

 pruning. Planning so human activity areas are 

 away from hazard trees can reduce risk with- 

 out altering the trees. 



Douglas-Fir 



Ejects of laminated root rot differ with 

 site and use — Laminated root rot is wide- 

 spread in southern British Columbia, Wash- 

 ington, Oregon, western Montana, and north- 

 em Idaho. It is believed to have co-evolved with 

 its hosts, making it a natural part of many for- 

 est ecosystems. It neither destroys huge ex- 

 panses of forest nor threatens the existence of 

 host species, but it does cause subtle, persis- 

 tent growth loss and mortality. The effect on 

 its primary host, Douglas-fir, varies with the 

 use or setting of the trees. When disease pock- 

 ets are small and scattered, they increase the 

 structural diversity and benefit wildlife and un- 

 derstory plants. Large root-disease pockets in 

 areas designated for timber management cause 

 significant economic loss. In settings such as 

 parks, around homes, or along well-traveled 

 roads, the disease can threaten life and prop- 

 erty. 



Douglas-fir beetle increases after distur- 

 bances — ^Douglas-fir beetle is the most impor- 



Douglas-fir beetle attacks large groups of 

 Douglas-fir only when large amounts of food 

 (downed trees) becomes available after 

 windstorms, fires, or logging. 



Douglas-fir beetle activity decreased in 1 995 in 



western Washington, source: Cooperative Aenal Survey, 

 Washington Department of Natural Resources and USDA Forest Service. 



tant bark beetle of Douglas-fir. In western 

 Washington, it attacks Douglas-fir 60 years old 

 or older; low populations are always present. 

 When populations are low, the beetle is rela- 

 tively nonaggressive, attacking recently killed 

 (windthrown, snow-broken) or dying (root-rot 

 infected, defoliated, drought-stricken, fire- 

 damaged, wounded) trees. When many fresh 

 logs become available in a short period, from 

 such events as windthrow, fires, or logging, the 

 beetles can reproduce in them and quickly 

 reach outbreak populations. They can then 

 attack and kill healthy trees. Relatively pure 

 stands of Douglas-fir, 120 years old or older, 

 of low vigor from competition, drought, or dis- 

 eases, are most at risk from beetle attack. 



The 1995 cooperative aerial insect detection 

 survey reported more than 2,000 trees killed 

 by Douglas-fir beetle on about 3,000 acres in 

 western Washington, a three-fold decrease 

 from 1994. Because aerial surveyors detect 

 tree condition based on changes in foliage 

 color, trees that quickly lose their needles may 

 not be recorded. 



Fog and off-site trees create an ideal 

 environment for needle disease — Swiss 

 needle cast is a native disease of Douglas-fir 



Washington — 47 



