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UBC Theses and Dissertations

The effect of some environmental factors on the morphological characteristics of western hemlock seedlings (Tsuga heterophylla (Raf.) (Sarg.) Soos, Joseph


The objective of the study reported in this thesis is to assess the influence of light and site quality on the morphology of western hemlock Tsuga heterophylla (Raf.) Sarg. seedlings. The importance of western hemlock to the present and future economy of British Columbia is emphasized. The silvical literature on the species is reviewed. The inadequate treatment given western hemlock in the technical literature is noted and the point is made that, as the hemlock forests are exploited and new forests regenerated, information on the silvical characteristics of the species will be needed. At the present time, knowledge of the silvics of western hemlock is very limited. This thesis attempts to add to knowledge in that field with particular reference to some factors (light, microsite and site) which influence the juvenile growth of western hemlock on the University of British Columbia Research Forest, near Haney, B.C. The effect of light intensity was studied through measurements of natural regeneration growing on 10 plots, under full light and under different degrees of canopy closure, in a 77-year-old stand. Measurements included height, diameter and number of green and dead branches. The influence of different microsites was studied on three-year-old wild seedlings and on 1 + 1 planted seedlings, with particular reference to height, stem diameter at ground level, number of branches, length of needles, angle of branches, diameter of branches, weight and depth of roots, and root/shoot ratio. Four-and five-year-old wildlings growing on plots with known site indices were studied with particular reference to maximum needle length and branch angle of last year's shoots. The results indicate that diameter and height growth increased directly with increased light and that seedlings cannot survive with less than ten per cent of full light (measured on cloudy days). The average minimum light intensity was found to be 117 foot-candles for a 12-hour period on bright days. Seedlings studied on five types of microsites showed significantly different external characteristics in height, diameter, maximum length of needles and angle of branches of the last internode. These characteristics were then studied on planted wildlings of local provenance on plots of known site indices. The results show that, after two years, the morphological characteristics of hemlock planted on different sites, were modified to levels associated with site quality. These modifications involved branch angle, maximum needle length, and height growth. It was concluded that, within a particular provenance, the influence of environment is of greater significance than hereditary factors, in superimposing modifications on the basic form of western hemlock seedlings. The possibility of using branch angle and maximum needle length to estimate site quality is noted.

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