• Witter, John A.
  The University of Michigan
  
• Lynch, Ann M.
  The University of Michigan
  

Numerous studies in Eastern North America during the last 40 years have recorded the amount of tree mortality in individual spruce-fir stands during outbreaks of the spruce budworm (Witter et al. 1984). Mortality in mature balsam fir stands often ranges from 70 to 100 percent; in immature stands, mortality often ranges from 30 to 70 percent (MacLean 1980). However, mortality in an individual stand can be less. High mortality is more likely in stands with given characteristics. A number of rating systems have been developed to assist land managers in predicting the vulnerability of spruce-fir stands to the spruce budworm. This handbook describes the objectives and uses of rating systems in spruce-fir management and the most recently developed rating systems.