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Spruce Budworm Defoliation and Growth Loss in Young Balsam Fir: Spacing Effects on Needlefall in Protected Trees

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Age-dependent Weibull models were used to describe precise measurements of needlefall from a pair of protected plots of young, unspaced, balsam fir (Abies balsamea [L.] Mill.). These models showed that the age-specific rates of needlefall tended to increase with needle age throughout the observed crown. Where crown level effects were evident, needle lifespans were shorter in the lower crown than in the upper crown. The influence of crown level in the unspaced plots, however, was too inconsistent to be useful as a general predictor of needlefall rates. Comparing the results with previous work on spaced sample plots showed that spacing affected many aspects of needlefall. The mean needle lifespan of 5.3 yr (SE = 0.17) on the spaced sample plots was significantly greater than the 4.7 yr (SE = 0.22) estimated for the unspaced plots. These differences were most extreme in the lower crown. Spacing also influenced the earliest phase of needlefall. For needles under 2 yr, the mean age-specific rates of fall were negligible in the spaced plots, but were about 6%/yr in the unspaced plots. Thereafter, annual increases in the age-specific rates of needlefall were similar in the spaced and unspaced plots. Spacing also affected the pattern of year-to-year variation in needlefall. There was evidence of statistically significant trends in mean needle lifespans over time in the spaced plots, but not in the unspaced plots. For. Sci. 42(3):282-289.

Keywords: Life-table; Weibull; foliar biomass; mortality schedules

Document Type: Journal Article

Affiliations: Canadian Forest Service-Sault Ste. Marie, P.O. Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7

Publication date: August 1, 1996

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Also published by SAF:
    Journal of Forestry
    Other SAF Publications
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