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A study of variability in certain Douglas-fir populations in British Columbia. Tusko, Frank Ferenc

Abstract

The present study deals with an extensive morphological survey of variations in Douglas-fir (Pseudotsuga menziesii (Poir.) Franco) in a cross section of its northern distribution from the Pacific Coast eastward to the Rocky Mountains. Objective was to determine whether the morphological variations were significant, and hence applicable to problems of taxonomy and ecology of Douglas-fir. Mass-collections were taken from 854 individual trees from 43 sample areas across British Columbia. The following characteristics were investigated: degree of 'bract spreading'; colour of needles and ovulate strobili; cone length and diameter; cone scale angle; number of cone scales; cone specific gravity; bract and scale length; winged seed dimensions; needle length and thickness, and some of the gross characteristics of trees such as age, height, diameter, site class, crown density, degree of branch spreading, and amount of cone production. Field investigations were supplemented by seed-fall studies and by certain nursery and greenhouse investigations (shade-light treatments, seedling comparisons). Statistical analyses employing several procedures (t-test, F-test, Chi-square test, Duncan's test, correlation and multiple regression analyses) established the basis for discussions of the differences between coastal and interior populations of Douglas-fir, as well as geographical distribution of characters and their variability within the two geographical regions and the localities sampled. Statistical parameters of several morphological characteristics have been determined, as well as their correlations with climatic and site factors. Certain observations and considerations have also been made on the taxonomy and nomenclature of Dougla fir. The following conclusions are reached: Two subspecies of Douglas-fir can be recognized, viz. 1) P. menziesii (Mirb.) Franco ssp. menziesii. Coastal Douglas-fir; and 2) P. menziesii (Mirb.) Franco ssp. glaucescens (Bailly) Schwerin, Interior or Rocky Mountain Douglas-fir. An identification key for the two subspecies and a list of synonyms are also provided.

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