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This is a broad, quantitative comparison of 12 maple species, representing both canopy and subcanopy growth forms, grown under two ecologically relevant light environments. The maple seedlings responded mainly to light intensity; light quality plays only a minor role in the induction of shade characteristics. While a light-mediated trade off between light and dark reactions of photosynthesis was evident at the chloroplast level, this did not lead to similar differences in assimilaton rates. Gap-grown seedlings showed no apparent compromise in photosynthetic response to dim light and lightflecks. Seedlings of subcanopy trees trade off wood strength for increases in plant size while canopy seedlings sacrifice plant size for wood strength. The demand for greater wood strength in seedlings of canopy trees appears to pose a strong developmental constraint that delays maturation. Free of this constraint, subcanopy species can devote more resource to reach adult size quickly and at an earlier age.

Sugar maple trees were fertilized in June 1988 on an individual tree basis in an attempt to improve tree vigour. Fertilizers included K$ sb2$SO$ sb4$, a phosphate and base cations mix, and a commercial organic mix (Maplegro). No effect of fertilization was found on foliar nutrient concentrations and water status of trees during the 1990 growing season. This is possibly the result of dilution in tree biomass, the addition of non limiting nutrients or the experimental design. A positive effect of fertilization on growth was found for one site and, at another, fertilization was found to impair growth. Thus fertilization requirements of declining sugar maple are site specific. Soil Mg was higher around trees fertilized with Maplegro, and trees fertilized with K$ sb2$SO$ sb4$ had low leaf buffering capacities.

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Optimum nutritional levels for most commercial hardwoods of eastern Canada are unknown. This thesis dealt with the development of a method to determine nutritional standards using within site variation in tree growth and foliar chemistry. To this end, sugar maple (n = 87) and red maple (n = 39) trees were sampled in summer 2001 at the Station de biologie des Laurentides. Leaves were sampled for nutrients (N, P, K, Ca, Mg and Mn) and tree stems were measured for determination of basal area growth (BAG). Similar measurements for trees sampled annually during 1995--2001 were also used to measure the effect of annual variation on nutritional standards. A boundary line approach was used to assess tree growth response to nutrition using nutrient concentrations and Compositional Nutrient Diagnosis (CND) scores as predicting variables. A Basal Area Growth Index (BAGI) was computed using the live crown ratio to correct for the effect of stand density on BAG. An iterative and unbiased protocol was also developed to eliminate outliers. Optimum, critical and optimal range levels were derived from quadratic models significant at P < 0.15.

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Red maple seedlings grown from fruits collected from matched wet and dry sites from three physiographic regions of Virginia were flooded to test whether red maple seedlings derived from wet sites are affected differently by flooding than are seedlings derived from dry sites. Thirteen weeks of soil inundation on seedling growth found no interactions between flooding and maternal hydrologic condition. However, flooding significantly decreased leaf, stem, and root dry matter accumulation as well as height growth, leaf area growth, root to shoot ratio, mean relative growth rate, net assimilation rate, and mean leaf area ratio. Thirteen days of rhizosphere inundation as well as six days of recovery on seedling gas exchange determined that flooding significantly decreased photosynthetic rate and leaf conductance. A larger decrease in photosynthetic rate than in leaf conductance resulted in decreased water use efficiency and leaf limitation. There were no interactions between flooding and maternal hydrologic condition. Fourteen days of flooding decreased root aerobic respiratory capacity and root ethylene evolution, and caused shoot water potential to be less negative. As in the previous studies, no interaction between flooding and maternal hydrologic condition existed. Although rhizosphere inundation negatively affected the growth and physiology of red maple seedlings, there does not appear to exist any genetic differentiation between wet site and dry site populations affording either of the populations enhanced flood tolerance. Rather, red maple appear to have the species wide phenotypic plasticity to survive flooded conditions. / Master of Science