© 2001 Heron Publishing—Victoria, Canada
Mechanisms of Douglas-fir resistance to western spruce budworm defoliation: bud burst phenology, photosynthetic compensation
and growth rate
Zhong Chen (1, 2), Thomas E. Kolb (1, 4) and Karen M. Clancy (3)
1. School of Forestry, Northern Arizona University, Flagstaff, AZ 86011-5018, USA / 2. Dept. of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA / 3. Rocky Mountain Research Station, 2500 S. Pine Knoll Drive, Flagstaff, AZ 86001, USA / 4. Author to whom correspondence should be addressed (Tom.Kolb@nau.edu) / Received January 29, 2001
Summary
We compared growth rates among mature interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) trees showing resistance or susceptibility to defoliation caused by western spruce budworm (Choristoneura occidentalis Freeman), and among clones and half-sib seedling progeny of these trees in a greenhouse. We also investigated bud burst phenology
and photosynthetic responses of clones to budworm defoliation in greenhouse experiments. Resistant mature trees had a higher
radial growth rate than susceptible trees, especially during periods of budworm defoliation. Clones from resistant trees grew
larger crowns than clones from susceptible trees, whereas stem base diameter at the ground line and height did not differ.
Half-sib seedling progeny from resistant trees had larger stem diameter, height, and total biomass than progeny from susceptible
trees. Mean 5-year radial growth increment of mature trees was more strongly correlated with growth of seedlings than with
growth of clones. Clones from resistant trees had later bud burst than clones from susceptible trees, and budworm defoliation
of clones depended on the degree of synchrony between bud burst phenology and budworm larval feeding. Clones of resistant
and susceptible mature trees showed similar responses of net photosynthetic rate to 2 years of budworm defoliation. We conclude
that phenotypic differences in crown condition of Douglas-fir trees following western spruce budworm defoliation are influenced
by tree genotype and that high growth rate and late bud burst phenology promote tree resistance to budworm defoliation.
Keywords:
Choristoneura occidentalis, genetic variation, insect herbivory, photosynthesis, Pseudotsuga menziesii.
