• Margolis, Hank A.
  University of Laval
  
• Coyea, Marie R.
  University of Laval
  

The growth efficiencies (E; stemwood growth per unit leaf area) of balsam fir (Abies balsamea (L.) Mill.) trees from 20 stands were reconstructed over the 30-year period from 1960 to 1989 in order to determine if E could be used to predict tree mortality occurring during and after an epidemic of eastern spruce bud worm. Growth efficiencies were reconstructed based on the relationship between age and the number of annual growth rings in the cros sectional area of heartwood at breast height (R2 = 0.97) and on the previously demonstrated relationship between sapwood area and leaf area of balsam fir across a wide geographic area. Profile and logistic regression analyses demonstrated that apparent E (i.e., the historically reconstructed E) of surviving trees was greater than that of dead trees for every year of the 30-year analysis period.  For all trees (aged 11 to 46 years in 1960), both tree age and apparent E were significant factors prior to the epidemic. During and following the epidemic, several of the more standard mensurational variables (e.g., diameter and basal area growth) were also significantly associated with balsam fir mortality, but apparent E had the highest levels of significance. The results suggest that growth efficiency should be considered as part of standard forest inventories in the balsam fir zone because of its ease of measure and its apparent ability to provide a sensitive, physiologically based index of forest health.