• Effects of Defoliation by the Western False Hemlock Looper on Douglas-Fir Tree-Ring Chronologies

      Alfaro, R. I.; MacDonald, R. N.; Forestry Canada, Pacific Forestry Centre, Victoria, British Columbia; Department of Computer Science, University of Victoria, Victoria, British Columbia (Tree-Ring Society, 1988)
      Annual rings of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, which sustained 1 year of defoliation by the western false hemlock looper, Nepytia freemanii Munroe (Lepidoptera: Geometridae), showed a period of decrease in breast height ring width starting in the year that followed the damage. The magnitude of the decrease was related to the degree of defoliation: there was no ring width decrease on trees that were 0-10% defoliated; the decrease became progressively more noticeable in trees which sustained increasingly higher defoliation; and it was maximum in trees which sustained 91-100% defoliation. This period of reduction lasted 1 to 5 years and was followed by a period of above-normal growth which was related to defoliation in a similar manner: it was absent in trees 0-10% defoliated and maximum in the 91-100% tree defoliation class. Increase in defoliation caused a significant increase in index standard deviation, autocorrelation and mean sensitivity.
    • LaMarche, Valmore C., Jr.

      Tree-Ring Society, 1988
    • A Model for Tree-Ring Time Series to Detect Regional Growth Changes in Young, Evenaged Forest Stands

      Zahner, Robert; Department of Forestry, Clemson University, Clemson, South Carolina (Tree-Ring Society, 1988)
      Time-related region-wide growth declines or increases due to environmental impacts are not readily detected in rings of young trees because the intrinsic age-related decrease in ring widths is too prominent. Standardization techniques often obscure gradual growth changes due to exogenous factors such as regional atmospheric deposition. The model presented here uses a linear aggregate analysis of ring widths that permits age to be held constant while time varies. Rigorous testing requires tree-ring observations from evenaged stands exhibiting a range of current ages normal for the species and region. With age held constant, the key variable is simply the calendar year to which given rings are dated, a measure of the passage of time. An application of the model is given in which a 36 -year growth decline is identified in 20- to 40- year-old Pinus taeda L. in the southeastern United States.