Genetic improvement has been an integral part of loblolly pine plantation forestry in southern United States for about 60 years with focus on improving timber yield, wood quality, and pest and disease resistance. Advances in techniques of genetic selection, breeding, and propagation of planting material have made it possible to achieve genetic gains that are likely to result in significant changes in loblolly pine stand dynamics. Height-age relationships, height and diameter relationships and distributions, and intraspecific competition were investigated in second generation open-pollinated, controlled-pollinated, and clonal loblolly pine with an objective of characterizing the nature and magnitude of changes in these characteristics due to genetic improvement and clonal forestry. Genetic improvement and/or clonal forestry had no practical effect on parameters of the height-age and height-diameter relationships beyond the effect on the asymptote parameter of the Chapman-Richards and Korf equations that were used to model these relationships. Genetic improvement resulted in an increase in the mean of height distribution without a corresponding increase in the mean of the diameter distribution, but had no effect the variance and skewness of the distributions. Thus, growth and yield models in which basal area is a function of height at a specific age (site index) are likely to over predict genetic gains in basal area growth and volume yield. Increase in stand density resulted in an increase in variance of the diameter distribution of non-clonal stands but had no effect on the variance of the diameter distribution of clonal stands. Thus, diameter distribution of clonal stands may differ from that of non-clonal stands after crown closure despite the distributions not being different before and during early stages of crown closure. This study also evaluated methods that may be used to predict height growth of new genetic varieties and those that may be used to asses intraspecific competition in forest stands. Mixed-model approach of calibrating a height-age relationship to a new loblolly pine clone gave biased estimates for clones that were at the extremes of the distribution of the groups. The use of maximum likelihood with simulated annealing (MLSA) to evaluate competitive interactions among trees in loblolly pine stands gave non-unique estimates of optimum competitor selection radius. A simpler technique that uses Pearson correlations was proposed and was found to work better than MLSA. / Ph. D.

This study was designed to investigate the development of the crown architecture of six genotypes of loblolly pine across a variety of growing conditions, and also to investigate the stability of the crown ideotype for these genotypes over a range of site and silvicultural management regimes. The objectives were to determine whether the crown dimensions that determine the crown ideotype of four clones, a mass-control-pollinated family, and an open-pollinated family of Pinus taeda L. are consistent within their respective genotypes, and to determine whether those same crown dimensions and genotypes follow consistent patterns even when established on different sites with contrasting qualities and different silvicultural regimes. The study was conducted on a 5-year-old plantation with an initial spacing of 1,235 trees per hectare. The plots had not reached crown closure, which provided the opportunity to assess the crown characteristics of individual trees of each genotype and how they developed over in a variety of growing conditions, without the interactions of other individuals. The study was a split-split plot design with the whole plot divided between two sites of contrasting quality; one site established in the Virginia Piedmont and a second site established in the North Carolina Coastal Plain. The sub plots were divided between high and low intensity silviculture. The sub-sub plots were divided among the six genotypes of loblolly pine. Seventeen tree and crown characteristics were measured, and means were compared using analysis of variance and Tukey's HSD test. We hypothesized that the branch and crown attributes would follow consistent patterns among these genotypes on the two sites and between the two silvicultural regimes. The results generally confirm these hypotheses. When the genotypes were compared, interactions only occurred with total branches, internode length, total foliage mass, and total leaf area. Tree height, diameter at breast height (dbh), stem volume, and crown volume averaged 4.8 m, 7.5 cm, 0.03 m3, and 7.1 m3, respectively at the site in Virginia, compared to values of 4.1 m, 6.2 cm, 0.02 m3, and 4.9 m3 at the site in North Carolina. Tree height, dbh, stem volume, branch diameter, branch length, and crown volume averaged 4.7 m, 7.5 cm, 0.03 m3, 1.3 cm, 90.3 cm, and 7.3 m3, respectively under high intensity silviculture compared to values of 4.3 m, 6.2 cm, 0.02 m3, 1.1 cm, 68.7 cm, and 4.7 m3 under low intensity silviculture. There were differences among the genotypes in branch diameter, branch length, and crown volume, with the branch diameter of clones 1 and 3 averaging 1.2 cm compared to an average of 1.3 cm for clones 2 and 4. Branch length for clone 1 averaged 72.4 cm and clone 3 averaged 77.0 cm, while branch length for clone 2 averaged 83.3 cm and clone 4 averaged 86.7 cm. Crown volume for clone 1 averaged 4.9 m3 and clone 3 averaged 6.3 m3, while clone 2 averaged 7.1 m3 and clone 4 averaged 7.2 m3. These differences conform to the crown ideotype for these clones, where clones 1 and 3 were considered narrow crowned and clones 2 and 4 were considered broad crowned. The branch diameter and branch length of the open pollinated family (OP) was similar in size to the broad crowned clones (1.3 cm and 84 cm, respectively), while the branch diameter and branch length of the mass control pollinated (MCP) family was smaller than the narrow crowned clones (1.1 cm and 71.2 cm, respectively). Crown volume for the OP family was intermediate between the clonal ideotypes, averaging 5.9 m3, while the MCP family had the smallest crown volume, averaging 4.7 m3. A single-degree-of-freedom ANOVA comparing the two clonal ideotypes yielded similar results. There were interactions with branch diameter, total branches, internode length, and total leaf area, but the broad crown ideotype was larger in every measured parameter than the narrow crown ideotype. The lack of interactions and the general conformity to crown ideotype in this study indicated stability among these genotypes across this variety of growing conditions. / Master of Science

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