Crown structure, growth performance, nutritional characteristics, and their genetic parameter estimates in juvenile loblolly and slash pine

An understanding of growth, crown structure, nutritional attributes, and their interrelationships can provide valuable information regarding future opportunities for improving forest productivity. This dissertation focused on production ecology, genetics, and nutrition of two important and widely planted commercial timber species in the southeastern United States, loblolly pine and slash pine, as a basis to investigate the interspecific and intraspecific differences in growth strategies. Genetically improved loblolly pine, improved slash pine, and unimproved slash pine were managed under two levels of silvicultural treatments at two locations in north central Florida. Comparisons and contrasts were made at ages 3 and 4 years among the three taxa, while genetic parameters were estimated from 16 loblolly pine and 32 slash pine open-pollinated families to enhance the understanding of genetic architecture of the two species.; Loblolly pine trees had more branches, wider crowns, higher amounts of foliage biomass and leaf area, and overall growth than slash pine at both ages, but produced less volume per unit leaf area (804 cm3 wood/m2 leaf area) than improved slash pine (1,106) and unimproved slash pine (1,173). Differences in growth were associated with crown structural and nutritional attributes among taxa. Loblolly pine consistently had higher foliage N and P concentrations over the life cycle of a needle cohort, higher N, K, Mg, and Ca use efficiency for leaf area production, higher crown (foliage) nutrient content, and higher nutrient retranslocation efficiency for N, P, and K than slash pine.; Narrow-sense heritability estimates for most attributes for the two species were low to moderate. Both species had moderate heritabilities in leaf area (h2 = 0.25 and 0.28, respectively). Loblolly pine had higher heritability (maximum h2 = 0.83) for foliar N concentration, but lower heritabilities for foliar Ca and Mg concentrations than slash pine throughout an entire leaf life cycle. Loblolly pine also had higher heritabilities in N and P use efficiency (loblolly pine h2 = 0.41 and 0.27, respectively), but was lower for Ca and Mg use efficiency than slash pine (slash pine h2 = 0.32 and 0.26, respectively). Genotype x environment interactions were not important for most traits except those for crown structure in loblolly pine. Genetic and environmental correlations between growth and crown structural attributes in loblolly pine and between growth and nutritional attributes in slash pine were all positive and low to moderate. Results from this study have provided a comparison of growth strategies that can be used to select species suitable for plantation establishment at different locations and management intensities and to evaluate potential traits for tree improvement programs.