Laminated root rot creates differerit-sized openings, as 

 shown in this map of a 50-year-old Douglas-fir stand in 

 the Forest Grove District, Oregon Department of Forestry. 



Source: Oregon Department of Forestry survey. 



Laminated root rot causes tree mortality and 

 growth loss; it also predisposes trees to 

 windthrow. Because the disease spreads from 

 root to root and affects groups of trees, it com- 

 monly creates canopy openings of various 

 shapes and sizes. These openings allow light 

 to penetrate to the understory, stimulating 

 growth of herbs, shrubs, and tree species re- 

 sistant to the disease. Trees killed by the dis- 



ease provide short-term snags and 

 logs, which benefit many wildlife spe- 

 cies. The increased diversity and ben- 

 efits to wildlife partially offset the huge 

 volumes of timber lost to this disease 

 annually. 



Laminated root rot intensifies on a 

 site when Douglas-fir or another 

 highly susceptible species are planted 

 in an infested area and the fungus, 

 which survives for decades in buried 

 roots, grows from infected roots onto 

 the roots of the newly established tree. 

 Some of the most severe damage is in 

 the Coast Range, where diseased 

 stands were burned or clearcut and 

 planted with Douglas-fir. Current 

 management emphasizes planting or 

 retaining resistant or immune species 

 and carefully designing silvicultural 

 systems to prevent blowdown after 

 thinning. 



Armillaria and black stain root dis- 

 eases are far less abundant and dam- 

 aging than laminated root rot but oc- 

 casionally cause significant damage in 

 young Douglas-fir plantations, par- 

 ticularly those stressed by poor plant- 

 ing or soil compaction. Both diseases 

 are often found on the edges of lami- 

 nated root rot patches. 



Swiss needle cast damages 

 coastal Douglas-fir — Swiss needle 

 cast is a native foliage disease of Dou- 

 glas-fir throughout the Coast Range 

 and western Cascades. It impairs the 

 tree's ability to regulate water loss and 

 causes premature loss of needles. Se- 

 verely damaged trees grow poorly and 

 may die. 

 In most areas, the disease is of little conse- 

 quence, causing premature shedding of 3- and 

 4-year-old needles. Since the early 1980s, 

 however, thousands of acres of Douglas-fir 

 plantations along the north coast have shown 

 increasingly severe damage from this disease. 

 In late winter and early spring, diseased plan- 

 tations are noticeably yellow to brownish yel- 



Oregon — 27 



