Loblolly pine (<i>Pinus taeda</i>) productivity on wet flats of the lower coastal plain of Virginia is largely affected by the presence of high water tables and infertile soil. Site preparation by bedding and ditching can alleviate high water tables and increase aerated soil rooting volume, enhancing pine productivity. Fertilizing and liming may improve soil fertility by increasing available nutrients and soil pH. The purpose of this study was to evaluate two widely used site preparation methods, bedding and ditching, and to study the effects of fertilizer added at plantation age 9 years. Three site preparation treatments, on jurisdictional wetlands near Franklin, VA, were evaluated for their effects on water table depths and rotation-aged loblolly pine growth and yield. The study consisted of three blocks of three 4-ha plots each; all blocks had been harvested and chopped and burned in 1969. The treatments were none (control), bedded and ditched. In 1978, fertilizer treatments were applied to four-O.l0 ha subplots in the center of the 4-ha plots. Treatments were none (control); P; N and P; and N, P, and lime. Water table levels were measured biweekly during the growing season and monthly, thereafter, for the first three years and at age 23 years. A 12.5-percent inventory of overstory diameters with a subsample of total heights was completed for all species on each plot. / Master of Science

The influence of thinning at age eight on the photosynthetic rate, needle conductance, xylem water potential, water use efficiency and growth of loblolly pine trees was studied during their ninth and tenth growing seasons. Litterfall dynamics were monitored throughout the study period as well. At the end of the second post-thinning growing season, trees in thinned plots had greater stem diameters, greater live crown ratios, greater live crown diameters and greater average volumes and basal areas than did trees in control plots. Significant physiological changes due to thinning were observed only in the lower crowns where needles were found to adapt to the sudden increase in available light by adjusting their physiology to resemble that of sun needles. Lower crown photosynthesis and needle conductance in thinned plots were more similar to upper crown values for these parameters than to lower crown, control plot values. Foliage produced during the current year and measured after full elongation had a higher average photosynthetic rate, needle conductance and lower average water potential than did foliage in its second growing season during both 1988 and 1989. Additionally, the water use efficiency of current-year foliage was significantly greater than that of the second-year foliage. In both thinned and control plots, significant diameter growth and photosynthesis continued throughout the dormant season although at a slower rate than during the growing season. Litterfall timing did not differ between thinned and control plots, nor did the amount of litterfall per unit basal area during the first year following thinning. Partial second-year data suggest that subsequent litterfall amounts will mirror the greater average crown size in thinned plots. / Master of Science

Although there remains some controversy as to the benefits of individual tree growth and yield prediction models over stand-level models, individual tree models still have wide acceptance. A generalized thinning response variable which can account for the intensity of thinning, as well as the age of the stand at the time of thinning and the time elapsed since thinning, was applied to two existing models for loblolly pine (Pinus taeda) in cutover site-prepared plantations. A site index equation for predicting mean total height of dominant and co-dominant trees and a diameter increment model were developed to incorporate the thinning response variable. New fits of height increment and mortality functions to the available data were also completed. Separate mortality functions were fit to data from unthinned and thinned stands. The base models for this analysis were from the individual tree growth simulation model PTAEDA2. Evaluations for predictive ability of these models were done in a reduced version of the growth simulator which was modified to accept external data. The mean total height model had improved predictive ability over the original PTAEDA2 model for this variable. The diameter increment model produced no significant improvement in simulation comparisons. Fitting the two mortality functions to the multiple observation data resulted in the reduced predictive ability of the simulator compared to the original mortality model from PTAEDA2 which was fit to data from unthinned stands only. / Master of Science

Empirical and theoretical relationships between tree crown, stem and stand characteristics for unthinned and thinned stands of planted loblolly pine were investigated. The individual tree crown measurements of crown diameter (CD) and crown projection area (CPA), and stand level measurement of the sum of crown projection areas (SCPA) were particularly important in contributing to high levels of model fit and prediction abilities of common stem and stand characteristics. As these crown measures developed over time so did corresponding stem and stand attributes. The results were similar for trees and stands located in unthinned or thinned situations; however, a limited range of data may have accounted for these similarities. The stem attributes modeled included basal area and diameter and associated growth, while the stand attributes modeled were basal area and mean dbh and associated growth. Models were also developed for the individual tree crown characteristics of CD and growth, CPA, and height to crown diameter, and for the stand level crown attributes of SCPA and growth, mean crown projection area and mean height to crown diameter. Several common competition indices were adapted to include crown information and various structural changes. The most effective competition measures in helping to predict basal area growth were point in time crown measures of SCPA and CD for trees located in unthinned stands and SCPA and CPA for trees located in thinned stands. Lastly, the effects of planting rectangularity on stem basal area growth were investigated. Two measures of rectangularity were calculated: one dealing with the ratio of distances between adjacent competing trees and another involving the ratio of the major and minor axis distances of a subject tree's crown diameter. Depending on the age of the stand,. these measures of rectangularity were found to be significant in negatively affecting stem basal area growth of trees located in unthinned stands. / Ph. D.

Seedlings of two P. rigida and four P. taeda families and six P. x rigitaeda crosses were grown in a greenhouse under two moisture regimes. Water stress decreased growth in every case in every variable measured. Water stress also elicited some genetic differences in the pitch pine and loblolly pine that were not apparent under the non-stressed treatment. The major differences between pitch and loblolly seedlings seemed to be primarily a function of large differences in seed size. Free growth may also play a major role in differences between the two species. The theory that allometric coefficients are a good indicator of growth under moisture stress was not substantiated by this experiment. In addition, k-values were found to remain relatively constant despite changes in moisture stress. It appears that genetic variance components in P. x rigitaeda may have importance under one set of environmental conditions, and be unimportant in another. Inter-relationship of crosses and confounding of genetic expectations, however, make it difficult to speculate which variance components are most important under moisture stress. Correlations were made between seedling growth characteristics and 1, 2, 3, 4, 5 and 7 year height and a 7 year volume index. Many significant correlations were found with 7 year height and volume. These correlations indicate that greenhouse experiments may be useful as an early genetic screening technique in P. x rigitaeda. / M.S.

Drought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.

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No description available.

Drought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.