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UBC Theses and Dissertations

Use of competition indices in the selection of western hemlock plus trees Thomas, Charles E.


Western hemlock's primary role in an integrated forestry operation is in high density stands which produce a large cubic volume in relatively short rotations. This implies an efficient use of growing space, an important characteristic of the future tree. Selections of individual trees for inclusion in an improvement program should reflect this species management format. The objective of plus tree cruising is to select trees which are phenotypically superior for use in tree improvement breeding programs. The possibility of obtaining a 10-15% improvement in a selection category without waiting 20 to 40 years for results of progeny tests seems economically tempting. Unfortunately, environmental and genetic components of variability in a given trait resist separation in field selections. The objective of this study was to develop selection criteria which reflect two important characteristics: a) rapid growth rate and b) efficient utilization of space or growth under stand competition. ^Permanent sample plots in coastal British Columbia were used to investigate competition, crown characteristics and growth increment in even-aged, second growth stands of western hemlock. Several currently available competition indices were used in five year basal area increment regressions. A regression weighting procedure is described which allows the selection of trees having growth residuals larger than a prescribed confidence interval. The entire plot serves as an environ- mental base line (for selection). A second approach utilizes low level 70 mm aerial photography of crowns. Crown efficiency regressions are developed based on current crown area and five year basal area increment. Again a confidence interval is established with which to select the plus tree candidate. In an additional phase of the study, previously selected trees were visited with the goal of evaluating crown attributes on the basal area increment of these trees. One or more check trees were selected near each of the prior selections; these trees were compared with respect to growth, height, crown area projection, and length of crown. No statistical differences could be found between the two groups reaffirming the value of initial selection intensification.

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