Spruce-fir ecosystems of the eastern United States interest scientists because of reported changes in population growth. Whether red spruce (Picea rubens Sarg.) populations are declining because of disease, pollution or environmental stress or experiencing natural changes in stand development is unclear. This research examined the growth and physiological responses of red spruce seedlings to changes in atmospheric CO₂ water and nutrient availability to determine the response of this species to potential climatic changes. Red spruce seedlings were grown from seed for 1 year in ambient (374 ppm) or elevated (713 ppm) CO₂ in combination with low or high soil fertility treatment, and well-watered or water-stressed conditions. Red spruce seedlings grown with limited nutrient and water availability increased growth in elevated CO₂ as did seedlings grown with high soil fertility treatment and ample water. At 12 months of age, elevated CO₂-grown seedlings had greater dry weight, height, diameter and specific leaf weight than ambient CO₂-grown seedlings. Seedlings that formed a bud in elevated CO₂ at 5 months of age produced more total fixed growth than seedlings grown in ambient CO₂. Mean relative growth rate was greater in elevated than ambient CO₂-grown seedlings only from 3 to 5 months of age. Growth was greater at 12 months despite a lower photosynthetic rate in elevated CO₂-grown seedlings compared to ambient CO,-grown seedlings. Transplanting seedlings from 175-cm³ pots into 646-cm³ pots at 7 months did not change growth and physiological responses to elevated CO₂ at 12 months. Dry weight allocation patterns to leaf, stem and root were not influenced by growth in elevated CO₂ for 1 year. Drought-conditioning had a greater influence on the physiological responses of red spruce to decreasing water potential than did growth in elevated CO₂. Results from this research suggest that red spruce seedlings will grow bigger faster in a future elevated CO₂ atmosphere even if water and nutrients are limiting. / Ph. D.