As a result of these changes east of the Cascades in Washington and Oregon, disturbances no longer occur with the same frequency and intensity as in the past. Drought periods in the late 1980's and early 1990's, coupled with changes in forest structure and species composition, have contributed to increased susceptibility to insects, diseases, and fire. Bark beetle mortality, associated with tree stress and overcrowded stands, is more prevalent. Many root diseases are more widespread and destructive because of past harvest practices and the resulting changes in forest structure and tree species compostion. Similarly, 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.
Dwarf mistletoes are more severe where fire has been suppressed.
Before the 1900's, fires were frequent and reduced or eliminated dwarf mistletoe infestations. Fire is less frequent now but much more devastating on low elevation, dry sites because of fuel buildup. Solving these forest health problems in Washington and Oregon involves cooperation and interaction among groups with diverse viewpoints, so the values that are held for these forests can be maintained.