At least 43% of the Douglas-fir stands east of 

 the Cascades are estimated to be infected with 

 dwarf mistletoe. Infections are more widely 

 distributed and more severely damaging than 

 ever before. 



Ecologically important features of the dwarf 

 mistletoe are the wildlife food and habitat their 

 flowers, seeds, and witches brooms provide. 

 Brooms, which are caused by the reaction of 

 the host tree to hormones produced by the 

 parasite, are large masses of branches, twigs, 

 and needles. Brooms are often retained on the 

 tree after healthy branches are shed and pro- 

 vide dense platforms, either close to the tree 

 trunk or scattered about the crown. Brooms 

 are used for nesting, roosting, and hiding cover 

 by small mammals and birds, especially owls, 

 hawks, and grouse. 



Drought, defoliation, and disease con- 

 tribute to susceptibility to bark beetles — 

 In eastern Washington, the Douglas-fir beetle 

 normally breeds in felled, injured, or diseased 

 trees. Drought, root diseases, and repeated 

 years of defoliation by western spruce bud- 

 worm increase the susceptibility of Douglas- 



fir to this beetle by reducing the tree's ability 

 to resist attack. Mortality is widely scattered 

 when beetle populations are low, but outbreak 

 populations can kill apparently healthy trees 

 over extensive areas. 



The fir engraver infests true firs in eastern 

 Washington. It attacks pole-sized and mature 

 trees, causing significant mortality during out- 

 breaks. Outbreaks often occur during and af- 

 ter periods of drought. Trees with root disease 

 are especially susceptible to attack. Trees de- 

 foliated by western spruce budworm also are 

 likely to be attacked. The fir engraver com- 

 monly breeds in slash and windthrown trees. 



Pines 

 Mountain pine beetle causes mortality of 

 many pines — Mountain pine beetle occurs 

 throughout the range of pine in the Pacific 

 Northwest. Infestations have resulted in ex- 

 tensive mortality over large areas. In 1995, 

 mountain pine beetle in eastern Washington 

 was reported to have killed 406,000 trees of 

 four different species of pine on 201,000 acres. 



12 



Precipitation 

 NE Washington 



— Total annual 

 r ; 



Year 



80 



■^ 60 



O -O 



_l 1- 



E-Q 

 ^ c 

 O O 

 > = 



E 



40 



20 



Fir Engraver 



400 



300 



200 



100 



3^ 



Year 



Precipitation in northeastern Washington was lower than normal most years between 1 985 and 

 1 994 (left). Fir engraver activity was also highest during this period (right), source: Washington Depannnent of 



Natural Resources (precipitation data); Cooperative Aerial Survey.Washington Department of Natural Resources and USDA Forest Service (insea data). 



Washington — 56 



