• Baskerville, G.L.
  Canadian Forestry Service
  
• MacLean, D.A.
  Canadian Forestry Service
  

Budworm-caused tree mortality and stand recovery over a 20-year period following a spruce budworm, Choristoneura fumiferana (Clem.), outbreak were examined in an immature balsam fir, Abies balsamea (L.) Mill., stand in northwestern New Brunswick. Tree mortality peaked in the sixth and seventh year of the budworm outbreak and showed high variability within the stand, ranging from 18 to 80% of the total volume per hectare. There was no clear relationship between volume loss and stand characteristics, but mortality did tend to have a strongly contagious distribution in the stand. For individual trees, the period of defoliation was coincident with greatly reduced diameter growth. Within five years of cessation of defoliation, the crowns of surviving trees appeared fully recovered, and diameter and height growth were similar to that in unaffected stands. Although diameter growth showed a classic response to the reduction in stand density (thinning) and increased substantially beyond predefoliation levels, this growth was on smaller trees (because of the growth reductions during the outbreak) and there were fewer trees per hectare. Therefore, the recovery in terms of volume per hectare was poor, and only one plot had regained its predefoliation volume 15 years after defoliation ceased. Projection of stand development to age 75 years further suggested that on average, the plots which suffered budworm-caused mortality and growth loss would have only slightly more than one-half the projected volume without defoliation.