Mortality and top-kill in Douglas-fir following defoliation by the western spruce budworm in British Columbia

R. I. Alfaro


Surveys of mortality and top-kill caused by the western spruce budworm, <i>Choristoneura occidentalis</i> Freeman, in 65 stands of Douglas-fir, <i>Pseudotsuga menziesii</i> (Mirb.) Franco are reported. Top-kill was detected in 85% of the stands and 25% of the trees surveyed. Mortality amounted to 8% and less than 1% of the trees examined in the Vancouver and Kamloops Forest Regions, respectively. Both frequency of top-kill and mortality were related to the number of years defoliation in the stand and were higher on suppressed trees than on dominant or co-dominant trees. Younger stands sustained a higher incidence of topkill than older stands. Tree mortality was higher on steep slopes than on flat terrain. These results suggested that top-kill or mortality were the results of physiological stress on the trees, in addition to the debilitating effects of defoliation.


western spruce budworm; <i>Choristoneura occidentalis</i>; Douglas-fir; <i>Pseudotsuga menziesii</i>

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Alfaro, R.I., G.A. Van Sickle, A.J. Thomson, and E. Wegwitz. 1982. Tree mortality and radial growth losses caused by the western spruce budworm in a Douglas-fir stand in British Columbia. Can. J. For. Res. 12:780-787.

Alfaro, R.I., T.L. Shore, and E. Wegwitz. 1984. Defoliation and mortality caused by western spruce budworm: Variability in a Douglas-fir stand. J. Entomol. Soc. Brit. Columbia 81:33-38.

Alfaro. R.I., A.J. Thomson, and G.A. Van Sickle. 1985. Quantification of Douglas-fir growth losses caused by western spruce budworm through stem analysis. Can. J. For. Res. 15:5-9.

Dixon, W.J. and E.J. Massey, Jr. 1957. Introduction to statistical analysis. McGraw-Hill Book Co. 488 pp.

Fiddick, R.L. and G.A. Van Sickle. 1979. Forest insect and disease conditons. British Columbia and Yukon/1979, Can. For. Serv. Pac. For. Res. Cent. Inf. Rep. BC-X-200.

Harris, J.W.E., R.I. Alfaro, A.G. Dawson, and R.G. Brown. 1985. The spruce budworm in British Columbia 1909-1983. Can. For. Serv. Pac. For. Res. Cent. Inf. Rep. BC-X-257.

Scott, D.R.M., P.M. Crimp, and R.L. Johnsey. 1980. Growth impacts on host trees due to western spruce budworm defoliation on the east slope of the Washington Cascades. Canada-U.S. Spruce Budworms Research Program (CANUSA). Final report for 1979-1980. 111 pp.

Shepherd, R., J.W.E. Harris, G.A. Van Sickle, L. Fiddick, and L. McMullen. 1977. Status of western spruce budworm on Douglas-fir in British Columbia. Can. For. Serv. Pac. For. Res. Cent., Pest Report.

Thomson, A.J., R.I. Alfaro, and G.A. Van Sickle. 1982. Evaluating effects of western spruce budworm on Douglas-fir volume growth. Can. For. Serv. Res. Notes 4:24-25.

Van Sickle, G.A.. R.I. Alfaro, and A.J. Thomson. 1983. Douglas-fir height growth affected by western spruce budworm defoliation. Can. J. For. Res. 13:445-450.

Wesolowsky, G.O. 1976. Multiple regression and analysis of variance. John Wiley & Sons. 292 pp.


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