Insects and Disease 



Insects and disease were attacking trees on 319,000 acres or 27 percent 

 of the commercial timberland in 1978. Both the growth (vigor) and the 

 mortality rate of a forest are affected by the amount of insect and disease 

 activity. Bark beetles were found on more acres than any other insect or 

 disease problem. Diseases that cause rot were the most common problem in 

 old-growth sawtimber stands, but bark beetles were the most common problem 

 in all other stand size classes (see Table 24). 



Table 23. Average potential productivity per acre by forest type for commer- 

 cial timberland. Working Circle 3 (cubic feet/acre) . 



Forest Type Average Potential Productivity Net Growth 



(cubic feet/acre) (cubic feet/acre) 



Douglas-fir 54.1 25.1 



Lodgepole pine 59.6 66.4* 



Ponderosa pine 44.1 16.0 



Subalpine fir-spruce 64.5 35.8 



Other softwood types 45.3 25.7 



All softwood types 53.8 31.8 



Aspen 57.2 26.9 



Cottonwood 44.7 27.1 



All hardwood types 52.1 27 .0 



All forest types 53.7 31.5 



*This particular statistic reflects the effects of a large amount of ingrowth. 



Table 24. Area of commercial timberland by stand size class and insect and 

 disease category, Working Circle 3 (thousand acres) . 



Insect and Disease Category 



Bark 

 Stand Size Class Unclassified Beetles Defoliators Mistletoe Rot Total 



thousand acres 



Old growth sawtimber 178.8 35.7 5.8 12.6 



Young growth sawtimber 340.8 41.3 20.5 4.3 



Poletimber 161.2 50.6 14.2 25.1 



Seedlings and saplings 145.5 6.3 8.3 6.6 

 Nonstocked 34.6 



Total 861.0 133.8 48,7 48.6 



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