1986-1990 



1991-1995 



Decreasing 

 Mortality 



Mortality for fve-year periods detected by annual aerial surveys. Trends can be seen, such as decreasing 

 mortality in the Blue Mountains (nordieastern Oregon) and increasing mortality in south<entral Oregon. 



Source: Cooperative Aerial Survey, Oregort Departmerit of Forestry.Washirtgton Department of Natural Resources and USDA Forest Service. 



average over the past decade on both federal 

 and nonfederal lands. Typical annual mortal- 

 ity in Oregon and Washington forests, based 

 on 60 years of inventory data, is about 0.5% 

 of the volume of wood present. The last in- 

 ventories of eastern Oregon and Washington 

 forests (excluding National Forests) show an- 

 nual mortality at 0.84% for eastern Washing- 

 ton and 0.97% for eastern Oregon. National 

 Forest inventory data show similar trends. 



Annual aerial surveys for insect damage 

 show that mortality visible from the air (mainly 

 overstory trees; understoiy trees are difficult 

 to see) has actually decreased in most of east- 

 ern Oregon and Washington over the past few 

 years, after a period in the late 1980s when 

 mortality from bark beetles was very high. 

 Reduced mortality in the last few years may 

 be due to increased summer rains which lessen 

 tree stress and to the collapse of the current 

 western spruce budworm outbreak. 



WEATHER AND ITS INFLUENCE 

 ON FORESTS 



Weather injluences forest health by directly 

 damaging trees and by affecting the ability of 

 trees to protect themselves against insects and 

 diseases. 



The climate of the Oregon and Washington 

 is generally mild with dry summers. Great 

 variation in local areas is due to the influence 

 of elevation, proximity to the ocean, the north- 

 south mountain ranges, and prevailing storm 

 paths. Differences in dominant vegetation re- 

 flect differences in climate across the region 

 and the effects climate and weather have on 

 plants. 



The climate of western Oregon and Wash- 

 ington is strongly seasonal with less than 20% 

 of the precipitation falling from May through 

 July, the growing season for trees. The coastal 

 areas have a maritime climate characterized 



Overview — 13 



