SUMMARY Forest conditions in Oregon and Washington have been steadily 

 changing for more than 100 years. Many disturbance patterns 

 in forest stands no longer occur with the same frequency or 

 intensity as in the past, and current patterns are often outside 

 the natural range of variation. Much of the change in distur- 

 bance regimes is due to fire suppression, harvesting practices 

 in the last century, and increased urbanization, industry, and 

 commerce. 



East of the Cascades • Outbreaks of defoliating insects, such as western spruce 



budworm and Douglas-fir tussock moth, are now larger, more 

 intense, and more frequent than in the past. 



• Bark beetle mortality, associated with tree stress and over- 

 stocked stands, is more prevalent. 



• Drought periods in the late 1980s and early 1990s, coupled 

 with overstocking, contributed to increased susceptibility to 

 insects, diseases, and fire. 



• Many root diseases and dwarf mistletoes are more widespread 

 and destructive because of past harvest practices and the 

 resulting changes in forest structure and tree species. 



• Fire is less frequent now but much more devastating on low- 

 elevation, dry sites because of fuel buildup. 



West of the Cascades • Incidence and damage by native forest pathogens, particu- 

 larly root diseases, have increased because of past forest 

 management practices. 



• Periods of drought have contributed to susceptibility of trees 

 to attacks by insects and pathogens. 



Southwest Oregon • The risk of fire and insect outbreaks has increased because of 

 fire suppression, overstocked stands, and periods of drought. 



• Two exotic diseases, white pme blister rust and Port-Orford- 

 cedar root disease, have significantly affected their host 

 species and how they are managed. 



Urban Forests • Introductions of exotic pests have Increased greatly over the 



past century with increased commerce, travel, and new people 

 moving to the Northwest. 



• Air pollution has increased in the Willamette Valley and Puget 

 Sound areas with increased population and industry. Ozone 

 and other pollutants can damage forests near — and even far 

 from — pollutant sources. 



• Stresses on urban trees from air pollution, mechanical injury, 

 and poor maintenance have increased in many cities and 

 towns. 



• Fire, wind, insects, and diseases are hazards to the trees, 

 people, and homes in the urban-forest interface. 



