. Hazard-rating systems in forest insect pest management : symposium proceedings, Athens, Georgia, July 31-August 1, 1980. Forest insects Biological control United States Congresses; Forest insects United States Analysis; Forest insects United States Management. Table balsam fir basal area after 5 years of attack by the spruce budworm estimated from original balsam fir basal area and percent nonhost basal area, trees 4 inches in and up Percent nonhost basal area 20 Original balsam fir, basal area in ftVacre 40 60 80 100 120 Dead balsam fir, basal area ftVacre 0 15 35 54 73 93 1
. Hazard-rating systems in forest insect pest management : symposium proceedings, Athens, Georgia, July 31-August 1, 1980. Forest insects Biological control United States Congresses; Forest insects United States Analysis; Forest insects United States Management. Table balsam fir basal area after 5 years of attack by the spruce budworm estimated from original balsam fir basal area and percent nonhost basal area, trees 4 inches in and up Percent nonhost basal area 20 Original balsam fir, basal area in ftVacre 40 60 80 100 120 Dead balsam fir, basal area ftVacre 0 15 35 54 73 93 112 10 11 30 50 69 89 108 20 7 26 46 65 84 104 30 3 22 41 61 80 100 40 18 37 57 76 95 50 14 33 52 72 91 60 9 29 48 68 87. Figure relation between dead (D) balsam BA per acre and two stand variables: original balsam fir (OB) BA per acre, and percent nonhost (NH) BA per acre from the regression equa- tion (see text). Turner (1952), who found a tendency for fir mortality to increase with the amount of white spruce in the softwood types. No increase in fir mortality with the amount of white spruce was noted in the mixedwood-softwood types in Ontario. Only half of the spruce-fir stands in the pres- ent study were more than 75 percent soft- wood; in the 1969 study nearly two-thirds were predominantly softwood. Data for the present study came from the southeast portion of the forest, while in the 1969 study data came from the north- west portion of the forest. A drought in 1976 may have accelerated the fir mortal- ity. Site index or age of balsam fir were not important variables (table 1). These findings confirm the relative importance of balsam fir and nonhost tree densities to fir mortality. They offer the land manager a tool to estimate poten- tial loss from spruce budworm in spruce- fir stands. The differences between the present and the 1969 model emphasize the importance of regional as well as temporal differences in spruce budworm outbreaks. RECOMMENDATIONS An assessment
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