Long-term forest response to changes in atmospheric CO2 will be largely determined by reproductive success of individual trees. Reproductive success is determined by maturation rate (ontogeny), as well as flower, pollen, and seed production. These components are all difficult to quantify in nature where tree canopies overlap and dispersal distances can be large. Individual variability among trees and inter-annual variability in seed production further frustrate efforts to evaluate tree regeneration. The objective of this dissertation is to compare ontogeny and fecundity among individual Pinus taeda L. trees growing in ambient or elevated CO2 (ambient plus 200ul l-1) since 1996. I use a combination of classical statistical and hierarchical Bayesian techniques to evaluate ontogeny and individual tree fecundity, accounting for the complexity of experimentation in nature over multiple years.

Trees growing in future levels of atmospheric CO2 for seven years reached reproductive maturation earlier and at smaller diameters than ambient-grown trees and experienced greater fecundity. Twice the amount of carbon was allocated to observed seed cones in the CO2 fumigated plots relative to ambient plots from 1997 to 2002 (means = 9733.8 g C per fumigated ring vs. 4658.4 g C per ambient ring). Large increases in seed production not met by shifting resource allocation from seed mass or nitrogen content. Although germination success varied among years and individual plots, there was no consistent difference between CO2 treatments. Trees growing in high CO2 also began producing pollen cones before ambient-grown trees. Pines growing in high CO2 produced more pollen per basal area than ambient-grown stands.

Increased pollen production may have significant implications for seed quality, gene flow, and human health. The results shown in this study demonstrate great potential for increased reproductive biomass in an important piedmont species. Shifting allocation to reproduction may have direct effects on tree growth and longevity, but could also alter competitive dynamics and trophic interactions. Long-term community response to changing CO2 concentrations will be primarily driven by species-specific reproductive success. The work presented here demonstrates significant potential for shifting individual resources in Pinus taeda, and also illustrates the need for a greater understanding of how tree fecundity affects ecosystem function.