Impact of defoliation by spruce budworms populations on radial and volume growth of balsam fir : A review of present knowledge : Dickenwachstum der Bäume

Wien

1981

3 Abb., 2 Tab., 17 Lit. Ang.

Unselbständiges Werk

673

200004872

Epidemic populations of the spruce duworm (Choristoneura fumiferana Clem.) habe resulted in severe defoliation of host tree species over much of eastern North America. This paper reviews the effects of defolation on radial and volume growth of balsam fir (Abies balsamea (L.) Mill.) trees and stands. Several studies since the 1920's have shown that growth increment is reduced about 50 to 75% by several years of severe defoliation. Recent studies of defoliation impact on balsam fir in eastern Canada and the United States have found that: 1) Reductions in volume increment of young fir trees were evident during the first year of defoliation, and severe defoliation for 2 years resulted in a 50% reduction in volume growth. 2) Expressed on a stand basis, stands which suffered light defolation (<20% of current foliage) for 5 years showed negligible growth loss, whereas severe defolation (>90% of current foliage) for 5 years resulted in a 60% annual growth loss. 3) Defoliation during a budworm outbreak in the 1950's resulted in greatly reduced diametzer growth and virtually no height growth. After the collapse of the outbrek, diamter and hight growth of surviving trees were similar or greater than that in unaffected stands. However, recovery on a stand basis was poor; only one plot out of 10 had regained its predefoliation volume 15 years after defoliation ceased.