Across the central and eastern United States, upland oaks are experiencing regeneration complications. This thesis comprises two studies evaluating challenges in regenerating upland oaks. One study evaluates upland Quercus spp., Carya spp., and Acer rubrum L. response to prescribed fire and impacts on seedling growth and mortality. This study found prescribed fire promoted oak growth when canopy cover was < 77%. Oaks displayed lower percent mortality and higher resprout capacity after fire compared to red maple. The second study investigates impacts of Microstegium vimineum presence on Quercus alba L., Liriodendron tulipifera L., and Acer rubrum L. seedlings under different light and moisture environments. Microstegium vimineum presence decreased growth of both sweetgum and red maple; white oak was less impacted, likely because of its conservative growth strategy and high-water use efficiency. Oaks’ conservative growth strategy may offer more resiliency compared to its competitors in response to prescribed fire and Microstegium vimineum.

A greater emphasis is being placed on hardwood management, yet there has been relatively little effort to develop growth and yield information for hardwood forest types. Measurements on permanent growth and yield plots collected in 1981, 1988, 1994, and 2006 in minor stream bottoms in Mississippi and Alabama were used to construct a stand level growth and yield model for red oak/sweetgum stands. The model predicts arithmetic mean diameter, quadratic mean diameter, trees per acre, basal area, total tree height, and cubic foot volume per acre for the total stand and by species. Different sets of equations were constructed depending on the amount of information known about a hardwood stand. Models were chosen based on significance of variables, coefficient of determination, index of fit, and biological trends. Predicted stand development patterns are discussed. These models will be base models for a complete diameter distribution growth and yield model.

Loblolly pIne (Pinus taeda) and sweetgum (Liquidambar styraciflua) were grown in miniature stands at 7.6-cm spacings outdoors in open-top chambers (4.6 m in diameter and 3.5 m tall) for 16 months. Treatments consisted of ambient- and elevated-CO₂ , drought-stressed and well-watered, and stand type (monoculture and 50:50 replacement mixture). Gas exchange was measured monthly, growth parameters bimonthly. Loblolly pine carbon exchange rate (CER) was positive throughout the winter in all treatments and averaged 83% of summer rates. Between November 1994 and April 1995, relative crowding coefficient (RCC) of pine stem volumes increased regardless of CO₂ or water availability. RCC of pine biomass increased in droughted stands relative to well-watered stands, while RCC of sweetgum showed the opposite response. Based on these results increased atmospheric CO₂ concentrations will not affect the competitive outcomes of loblolly pine and sweetgum mixed stands: loblolly pine will continue to be more competitive on dry sites, sweetgum on wet sites. CER of loblolly pine and sweetgum, as well as soil respiration, were consistently significantly greater in elevated-C02 stands. CER in upper-canopy foliage was significantly greater than that of lower-canopy foliage for sweetgum. Loblolly pine, but not sweetgum, demonstrated a significant canopy position x CO₂ interaction, with upper-canopy CER greater only in elevated-CO₂ conditions. No consistent acclimation of CER to elevated CO₂ was statistically significant for either species, although acclimation response was stronger in sweetgum than in loblolly pine. / Master of Science

Changes in light harvesting ability and other physiological responses could int1uence the competitive outcomes of tree species in a future elevated CO₂ atmosphere. Photosynthetic light response curves were constructed with a closed photosynthesis system (LI-COR, Inc. Lincoln, NB) in order to investigate the effect of growth in elevated CO₂ (746 μl⁻¹) and ambient CO₂ (379 μl⁻¹) on light responses, and seedlings were allowed to dry out to examine physiological changes to water stress. While drying out, photosynthesis was measured with a closed system (LI-COR, Inc. Lincoln, NB) and fluorescence was measured with a portable fluorescence measurement system (P.K. Morgan Instruments, Inc Andover, MA). No species showed significant increases In quantum yields or decreases in light-compensation points as a result of elevated CO₂. Photosynthesis declined in all species due to water but seedlings grown in elevated C0₂ maintained photosynthesis longer. Loblolly pine and red maple grown in e1evated CO₂ showed signs of photosynthetic acclimation. Photochemical efficiency of PSII declined with water stress in loblolly pine. Red maple and sweetgum showed no relationship between photochemical efficiency of PSII and simulated drought. Growth in elevated C0₂ did not influence this response in loblolly pine, but sweetgum started with a lower photochemical efficiency or PSII which increased significantly. / Master of Science