The effects of defoliation by western spruce budworm (Choristoneuraoccidentalis (Freeman)), on Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) radial growth at breast height and tree mortality are given. Four hundred and twenty trees were marked in an 81-year-old stand, and their defoliation levels were recorded annually from 1970 to 1980 in an outbreak that lasted from 1970 to 1974, inclusive. Forty-one trees were felled and dissected in 1977, 3 years after recovery began. The number of stems per hectare was reduced by 39.3% and basal area by 11.6% through mortality, most occurring among the small diameter, suppressed, and intermediate trees. Relationships were established between mortality and defoliation. Radial increments were examined, and the presence of four outbreaks during the life of the stand was detected. The combined effect of these infestations amounted to a loss of about 12% of the estimated potential diameter had not the insects been active. The most recent outbreak (1970–1974) caused a total of 10 years of subnormal growth, including 5 years due to defoliation and 5 years of recovery. The relationship between radial increment losses and defoliation intensity and duration is studied and quantified.

No abstract

No abstract

Periodic growth and volume losses in Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) trees in one stand defoliated four times in their lifetime by western spruce budworm (Choristoneuraoccidentalis (Freeman)) are reported. Losses were calculated by comparing periodic growth for the years of reduced ring increment with potential growth estimated using the IMPACT growth loss program. Proportional losses in stem radius and cross-sectional area remained approximately constant or declined slightly from tree top to base; losses differed at all stem levels among the infestations. Average gross volume losses per tree relative to the potential volume the trees should have reached at the end of each loss period were 17, 15, 8, and 13% for the 1920's, 1940's, 1950's, and 1970's infestations, respectively. In the last infestation, losses ranged from 9% in trees defoliated from 1 to 50%, to 18% in trees defoliated 91–100%. Cumulative tree volume losses, calculated by adjusting growth during all loss periods to their potential values, were estimated to be 44% of the potential volume the trees should have reached by 1977 had the trees never been defoliated. On a per hectare basis, the 1970's infestation in this stand caused an estimated 60 m3 (18%) loss, comprising 40 m3 (12%) owing to tree mortality and 20 m3 (6%) of growth deficit in the surviving trees.

An improved method of quantitative evaluation of pest-caused reduction of tree growth is described. Radial and height growth rates were measured from discs along the bole of the tree, and growth losses were evaluated by a computer program (IMPACT). The method is independent of site characteristics or competition effects. Use of the method was demonstrated for growth losses in Pseudotsugamenziesii attributable to defoliation by Choristoneuraoccidentalis, and with slight modification it may be applied to a range of tree-pest systems. A three-dimensional graphical procedure was used to display the growth pattern.

Sequential color slides of a Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) tree were taken over several years to record the progression of crown defoliation by Douglas-fir tussock moth (Orgyiapseudotsugata McDunnough) and foliage recovery. The slides were digitized using a microdensitometer and analysed with a GEMS-300 image analysis system in an effort to detect changes in the amount of crown foliage. Digital images were successfully registered (overlaid) to standardize comparisons of the tree-crown profile in the various photographs. Image analysis algorithms developed for airborne or satellite multispectral scanner data were used to detect changes in crown profiles. The decrease in the amount of defoliation over time after the initial severe insect attack, estimated by a variable threshold technique, was similar to ocular ground-based estimates by well-trained observers. The supervised maximum-likelihood classification technique was found not suitable in this study.

Cronartiumcomptoniae incidence was measured on 62 provenances of Pinusbanksiana and 77 provenances of P. contorta. Infection incidence varied among provenances in both hosts. Pinusbanksiana provenances beyond the geographic range of Comptoniaperegrina, and P. contorta provenances beyond the geographic range of Myricagale, were more susceptible than some provenances within the range of these alternate hosts. It is hypothesized that selection pressure is important in maintaining resistance to C. comptoniae.

Basidiospores of Pucciniastrum goeppertianum (Kühn) Kleb. are globose, 5.8 μ in diameter, smooth-walled, apiculate, and have granular contents. The cardinal temperatures for their discharge were found to be 10, 18 to 20, and 25 °C. Development of new brooms from infected blueberry rhizomes started late in May, but shoots tested monthly in the laboratory released spores only from the next January until mid-June. The natural overwintering requirements of the fungus were mimicked by storing broom material at −4 °C from December until February.On balsam fir needles at 15 °C, germination of basidiospores usually produced a single, short germ tube, and exceeded 40% after 7 h of saturation and reached 70% by 48 h. Repetitive germination, commonly seen on glass slides or water agar, may only be typical of the reaction on non-host substrates. Only current-year needles were susceptible to infection and only from bud break until early in the 5th week, (corresponding approximately to the period of shoot elongation) provided that a minimum of 6 h at 15 °C under conditions of saturation preceded any period of drying of the foliage surface.