UBC Theses and Dissertations
Assessing competition using absolute and relative growth rates and relative density of wood for red pine (Pinus resinosa Ait.) LaRocque, G.
Effects of competition among trees of red pine (Pinus resinosa Ait.) on tree growth and on the relative density of wood were examined. Data came from a spacing trial with initial spacings ranging from 1.2x1.2 m to 6.0x6.0 m; individual trees were measured for DBH, height, and crown dimensions at several ages. The first objective was to evaluate if relative growth rate (RGR) expressed the competitive status of stands better than absolute growth rate (AGR), which is normally used in forestry. Relative growth rate was found to be superior to AGR. While AGR was always positively related to tree size, RGR decreased with tree size before the onset of competition or when it was not too severe, and increased with tree size under severe competitive stress. This implies that small trees were more efficient than large trees at producing new biomass before the onset of competition. The effect of competition was to reduce the efficiency of small trees compared to large ones. The second objective was to examine whether different measures of crown efficiency rarely used in forestry were related to the competitive status of stands. The ratios of crown width to crown length, and of crown length to DBH, the ratio of AGR in DBH to crown width and to crown length, and the ratio of AGR in basal area to foliage biomass showed a pattern similar to RGR: a decrease with tree size before the onset of competition, and an increase with tree size after. Crown ratio showed little variation with tree size for a particular spacing until the onset of competition, and increased with tree size afterwards. The third objective consisted of examining whether the relative density of wood in red pine was affected by different initial spacings. Increment cores were sampled at breast height on 30 trees within every spacing and scanned on a direct reading X-ray densitometer to determine the relative density of the wood. Ring width, the relative density of the ring, earlywood and late-wood densities, minimum and maximum densities, and proportions of earlywood and latewood were analysed. The relative density of the rings and of the latewood zones and the proportions of early-wood and latewood were closely associated with the change in competitive status of stands. Furthermore, the changes in wood density were closely associated with the changes in crown ratio. RGR and measures of crown efficiency describe the competitive status of stands better than classical measures of growth. Their use for evaluating the response of stands under intensive management still remains to be investigated.
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