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UBC Theses and Dissertations

Ecological physiology of conifer seedling and sapling suppression by, and release from, competing vegetation Bigley, Richard Ernest


The overall objective of this thesis was to improve our understanding of the light environment associated with two of the major deciduous competitors of commercial conifer seedlings in low elevation coastal British Columbia, and the physiological response of young conifers to specific environments and changes in the environment. Studies were conducted to investigate: 1) seasonal and herbicide-induced changes in the light regimes beneath the canopies of two brush species, 2) growth and physiology of seedlings of three conifer species in several different deciduous brush environments throughout the year, and 3) changes in the physiology and growth of suppressed conifer saplings when different methods and schedules were used to reduce shading from an overtopping red alder canopy. Seasonal changes in the light quantity and quality were documented within salmonberry (Rubus spectabilis Pursch) and below red alder (Alnus rubra Bong.) canopies. The prediction of light attenuation within salmonberry canopies using the Beer-Lambert law was good for foliated canopies using leaf area index, and defoliated canopies using stem area index. As salmonberry leaf area increased, the ratio of red to far-red light declined exponentially. Growth of grand fir (Abies qrandis (Dougl.) Forbes), western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Douglas-fir (Pseudetsuga menziesii (Mirbel) Franco) seedlings decreased with increases in the canopy density of overtopping deciduous species. Physiological differences between conifer species and differences between overtopping canopy treatments declined in the autumn and winter. Based on the physiological measurements, suppression of the shade intolerant Douglas-fir seedlings was greatly reduced during the period that overtopping deciduous canopies were leafless. Animal damage reduces growth and probably increases the duration seedlings are under overtopping canopies. Suppressed Douglas-fir saplings released from overtopping by red alder canopies showed the greatest growth response when the alder canopies were removed in the spring; complete removal of the alder canopy during the summer had a predictably deleterious effect on the sapling physiology and growth. Herbicide injections resulted in a slower but predictable increase in conifer growth.

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