UBC Theses and Dissertations
UBC Theses and Dissertations
Geographic variation in picea glauca in British Columbia Roche, Laurence
The principal objective of the study is the determination of geographic variation in white spruce in British Columbia. Since variation within this species in British Columbia is greatly influenced by hybridization with other spruce species, an attempt is made to demarcate zones of hybridization, and evaluate its effect on variation in white spruce. In a preliminary chapter the literature pertaining to principles and concepts of taxonomic and genecological investigation is critically examined in relation to infraspecific variation in tree species. The conclusions of this chapter constitute the assumptions of the investigation. A second chapter summaries the literature pertaining to the phylogeny and distribution of the spruce species of British Columbia, Photoperiodicity in forest trees is discussed in the third chapter. Following the chapters referred to above the study is divided into two parts, A and B. Part A is a study of the growth behaviour of 150 populations of spruce grown in a relatively uniform environment during a period of two years. The seed, which was collected throughout the spruce complex of British Columbia, was sown at the British Columbia Forest Service research nursery on Vancouver Island in the spring of 1965. Detailed measurements were made during the growing seasons of 1965 and 1966. In the laboratory seed samples of the same populations were X-rayed to determine embryo development and subsequently germinated at 25°C. Further seed samples were germinated at 15, 20, and 30°C. Part B is a study of geographic variation in mature populations of white spruce, and refers principally to a biometrical investigation of variation in cone scale morphology which was carried out on a mass collection of spruce cones collected in 157 areas throughout the range of spruce in British Columbia during the summers of 1963 and 1964. On the basis of the results obtained in parts A and B the following general conclusions are made: (i) In regard to the white-Engelmann spruce complex in British Columbia the environmental pressures which result in microevolution, i.e. infraspecific variation, differ only in degree rather than in kind from the environmental pressures which result in macroevolution, i.e. speciation. (ii) The faculty for normal development and survival of white spruce, and its related forms, is conditioned by the cessation of growth and initiation of dormancy. (iii) Time of initiation of dormancy in a population in any one region where the species occurs naturally is conditioned by its genetic constitution. (iv) The genetic constitution of a natural population is predominantly determined by the photothermal regime prevailing in that region. (v) In so far as there is a difference in the photothermal regime between any two regions the genetic constitution of the spruce populations occupying those regions will differ. (vi) One of the most important external manifestations of this difference is the time of cessation of growth and initiation of domancy. On the basis of these general conclusions, recommendations are made in regard to the silviculture of white spruce and its related forms in British Columbia, and also in regard to the field testing of the spruce populations referred to in part A of this study.
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