Effectiveness of spruce budworm spraying in New Brunswick in protecting the spruce component of spruce-fir stands

Tree mortality and defoliation were examined in 45 spruce (Picea sp.) stands protected against damage by spruce budworm (Choristoneurafumiferana (Clem.)) and in 27 unprotected spruce stands in New Brunswick, and were related to tree, stand, and site characteristics. The "protected" and "unprotected" classes of stands were defined on the basis of any spraying in the last 5 years (1978-1982), but we also estimated the spray and budworm hazard history from 1973 to 1982 for each stand. Based on this total sample of about 17 000 trees, there was little difference in mortality levels of spruce or combined spruce-fir (Abiesbalsamea (L.) Mill.) between protected and unprotected stands. Spruce mortality was relatively low in both protected and unprotected stands, averaging about 13 and 20% of the total volume, respectively. Fir mortality was higher in unprotected than in protected stands, although fir formed only a minor component of most of the sampled stands. Both average mortality and range were similar among the four spruce types present in New Brunswick: black spruce (Piceamariana (Mill.) B.S.P.), red spruce (Picearubens Sarg.), hybrid red-black spruce, and white spruce (Piceaglauca (Moench) Voss). In examining the relation of tree mortality to stand and site characteristics, the strongest correlations were found between dead spruce-fir volume (cubic metres per hectare) and total stand volume (r = 0.85), and between dead fir volume and total fir volume (r = 0.75). No apparent relationships were observed between mortality levels and various indices of protection and budworm hazard. It should be emphasized in presenting these results that the spray program in New Brunswick has historically been designed to protect fir, so that any protection afforded to spruce would be entirely an incidental benefit from attention to the fir problem. Although our results do not reflect a failure of a clearly defined effort to protect spruce, we do recommend that further protection efforts for spruce in New Brunswick be reevaluated.