America were strongly fire dependent. Han'ey (1985) states that 

 certain budworms {Choristoneura spp.) have been a part of the 

 ecology of spruce-fir and pine forests of North America for 

 centuries, suggesting that outbreaks are a part of the natural con- 

 dition. Historical records and research show that outbreaks of 

 spruce budworm have occurred over the past 200 to 300 years at 

 many locations (Blais 1985, Fleming 1985). Several bark beetles 

 play a major role in forest ecosystems. 



The ecological roles of the more aggressive bark beetles are asso- 

 ciated with disturbances (drought, windthrow, etc.) and condi- 

 tions of the host trees. Populations of these beetles can increase 

 vei"y rapidly and develop into widespread outbreaks (Benyman 

 1982) covering very large areas, particularly where large stands of 

 even-aged host trees are involved, for example, mountain pine 

 beetle in lodgepole pine. Outbreaks of the southern pine beetle 

 were recorded as early as the I750's (Nettleton 1988). Dwarf 

 mistletoes, the most damaging disease agents of conifers in many 

 parts of the West, have evolved along with their hosts over thou- 

 sands of years (Hawksworth and Weins 1972). Decline diseases of 

 hardwoods in the East have an extensive history (Houston 1987, 

 Millers etal. 1989). 



Epidemics of some native pests are now exceeding historic levels, 

 largely due to past management activities that created forest 

 conditions favoring pests. Management activities that have led to 

 increased epidemics were discussed in the 1988 Forest Health 

 Strategic Plan: 



Management activities influencing forest pest outbreaks include 

 activities that, by design or accident, produce forest conditions favorable to survival or 

 growth of forest pests. There are many examples of management activities on forested lands 

 of the United States thai are responsible for some of the more destructive pest outbreaks. 

 Specific examples thalfrec/uenlly occurred in the past include off site planting; harvest 

 schedules beyond the entomological or pathological rotations for the species and area; plant- 

 ing susceptible varieties {or relying on natural vegetation) in areas of known disease occur- 

 rence; increasing stand densities; planting or encouraging the natural establishment of 

 extensive monocultures; failure to remove infested overstory trees during harvest; and fail- 

 ure lo provide a cultural substitute for the mosiac-creating effects of fire. Stand management 

 plans that do not address potential pest problems set up conditions fcjr pest outbreaks . . . 

 Silvicultural practices that manipulate vegetation in such a way as to maintain the vigor 

 of the forest could play a major role in achieving healthy forests. Sound management prac- 

 tices can greatly reduce a forest's susceptibility lo insects and diseases. 



Healthy Forests for America 's Future — A Strategic Plan 



