Belowground competition presents a threat to the production and sustainability of tree-grass ecosystems. Management scenarios designed to optimize the spatial and temporal distribution of soil resources will improve resource-use efficiency and promote greater co-production. We conducted three experiments to assess competition dynamics between loblolly pine and switchgrass. In a three-year field trial, loblolly pine and switchgrass were intercropped across varying competitive intensities. Interspecific competition decreased loblolly pine annual growth; however, establishing vegetation exclusion zones surrounding pines largely mitigated these effects. Switchgrass yields were less affected by interspecific competition compared to pines and land equivalency ratios indicated that with proper management co-production yields may exceed those of switchgrass monoculture. Switchgrass was a constant and significant competitor across all years while loblolly pine resource use was minimal in year 1 but increased in subsequent years. In a short-term greenhouse experiment, native soil was amended with biochar and inorganic N fertilizer and the effects of these amendments upon soil properties and switchgrass productivity were assessed. Biochar increased soil pH, total soil carbon, and soil moisture. However, N fertilization had negligible effects upon soil properties. Plant response to biochar was neutral to negative while N fertilization increased switchgrass foliar biomass but no interactive effects of the amendments were observed. Although the effects of biochar upon switchgrass production were trivial, its positive influence upon soil properties suggests a potential for mitigating competitive interactions. Finally, a field-scale study examined co-production of loblolly pine and switchgrass over two years in response to competition control, biochar, and N fertilizer. As expected, interspecific competition reduced soil resources and decreased plant productivity. Biochar increased total soil C and soil moisture levels but had relatively minor impacts upon other aspects of soil fertility or plant production. Nitrogen fertilization acidified soil pH and decreased total soil C and N but positively affected loblolly pine foliar N concentrations and switchgrass yields. A positive association between soil inorganic N and switchgrass yield suggests the species competitive influence may be increased with greater N supply.

For operational forest management, a forest inventory is commonly conducted to determine the timber stocking and the value of standing trees in a stand. With time and costs constraints, appropriate sampling designs and models are required to perform the inventory efficiently, as well as to obtain reliable estimates for the variables needed to make projections. In this dissertation research, a simulation study was conducted to extensively explore four important topics in forest inventories: selection of measurement trees in point samples, projection from plot- and stand-level aggregations, subsampling height for volume estimation, and updating stand projections using periodic inventories. A series of simulated loblolly pine plantations with varying degrees of spatial heterogeneity were generated at different stages in stand development. Repeated sampling was used to examine various sampling schemes and growth projection methods. Highlights for the four topics follow: 1. Stand total volume can be reliably estimated using measurement trees tallied by Big BAF, point-double sampling, or random selection of a specified number of trees. However, number of trees per unit area in small-size classes were overestimated across the three tree-selection methods when sample data were aggregated into diameter classes. 2. Plot-level and stand-level projections produced similar estimates for dominant height, basal area, and stems per unit area. As spatial heterogeneity increased, stand-level projections indicated a significant bias of predicted total volume compared with the plot-level projections. 3. Sampling intensity, stand age and spatial heterogeneity have greater influence on the reliability for total volume estimation compared to subsampling intensity and measurement error for height measurements. 4.The variability of total volume estimates increases with increasing projection length (i.e., longer time intervals between inventory entry points). However, the estimates of stand total volume can be greatly improved by updating the models with information obtained in periodic forest inventories, especially when the original models are not well calibrated. The results of this study provide useful guidance and insights for forest practitioners to design forest inventories and improve growth projection systems in operational forest management. / Doctor of Philosophy / For operational forest management, a forest inventory is commonly conducted to determine the timber stocking and the value of standing trees in a stand for management decisions, financial planning and fiduciary reporting requirements. With time and costs constraints, appropriate sampling designs and models are required to perform the inventory efficiently, as well as to obtain reliable estimates for the variables needed to make stand projections. Loblolly pine (Pinus taeda L.) is the primary commercial species in the southeastern United States. In this dissertation research, a simulation study was conducted to extensively explore several important topics in forest inventories, including selection of measurement trees in point samples, projection from plot- and stand-level aggregations, subsampling height for volume estimation, and updating stand projections using periodic inventories. A series of simulated loblolly pine plantations with varying degrees of spatial heterogeneity were generated at different stages in stand development. Repeated sampling was used to examine various sampling schemes and growth projection methods. The results of this study provide useful guidance and insights for forest practitioners to design forest inventories and improve growth projection systems in operational forest management.

Modeling growth dynamics of juvenile loblolly pine plantations can help to address important management decisions that have to be made in young stands. The present study addressed diameter and height prediction as well as crown development analysis as functions of independent variables such as site index, relative spacing and age for trees younger than ten years old. It was found that height prediction for trees one and two years old was a function of the products of the variables site index and age (or square root of age) and relative spacing and age (or square root of age). For trees three years old and older these were also the independent variables used to explain height prediction but in this case age (or square root of age) was another significant independent variable. In regard to diameter prediction it was observed that groundline diameter was a function of age for trees one and two years old; while this variable was also a function of site index and relative spacing for trees three, four and five years old. For trees older than five years old diameter at breast height was a function of age, site index and relative spacing. The analysis of crown development showed that for trees five years old and older variables like diameter at breast height, total height, age, site index and relative spacing were significant when crown ratio was the dependent variable. For trees younger than five years old, groundline diameter and the other same independent variables (i.e. total height, age, index and relative spacing) were again found significant when crown ratio was the dependent variable. / Ph. D.

Spatial analysis is of primary importance in forestry. Many factors that affect tree development have spatial components and can be sampled across geographic space. Some examples of spatially structured factors that affect tree growth include soil composition, water availability, and growing space. Our goals for this dissertation were to test the efficacy of spatial analysis tools in a forestry setting and make recommendations for their use. Reliable spatial analysis tools will lead to more effective statistical testing and can lead to useful mapping of spatial patterns. The data for this project is from simulated even aged loblolly pine stands (Pinus taeda L.). These simulated stands are grown at regular spacing and we impose a range of parameters on the stands to simulate many possible scenarios. In chapter 3 of this dissertation we perform a sensitivity analysis to determine if our methods are suitable for further research and applications. In chapter 4 we perform our analysis on more realistic data generated by a spatially-explicit stand simulator, PTAEDA 4.1. In chapter 3 we performed a statistical simulation of plantation stands without effects of competition and mortality. We used redundancy analysis (RDA) to quantify spatial variability, partial redundancy analysis (pRDA) to test for spatial dependence, and spatially constrained cluster analysis to map soil productivity. Our results indicated that RDA and pRDA are reliable methods and future evaluation is appropriate. The results from the spatially constrained cluster analysis were less clear. The success or failure of the clustering algorithm could not be disentangled from the success or failure of the selection criterion used to predict the number of clusters. Further investigations should address this concern. In chapter 4 we used PTAEDA 4.1, a loblolly stand simulator, to simulate a range of site conditions and produce data that we could use for analysis. The results showed that RDA and pRDA were not reliable methods and ready for the field. Spatially constrained cluster analysis performed poorly when more realistic data was used and because of this further use was uncertain. It was clear from the results that levels of variation and spatial pattern complexity of microsites influenced the success rate of the methods. Both RDA and pRDA were less successful with higher levels of variation in the data and with increased spatial pattern complexity. In chapter 5 we related the coefficient of variation from our simulations in (chapters 3 and 4) to two sets of real plot data, including a clonal set and open pollinated set. We then implemented a spatial analysis of the real plot data. Our spatial analysis results of the two comparable data sets were unaffected by genetic variability indicating that the primary source of variability across plots appears to be soil and other factors, not genetic related. / Ph. D.

Site index curves for natural stands and plantation stands of loblolly pine in the Southeast were constructed from temporary age height data by an anamorphic technique and two polymorphic techniques. These different systems of site index curves were evaluated using sectioned tree data. Evaluation results showed the anamorphic site index curves were best for the plantation stands, and the polymorphic curves constructed using a data stratification method were best for the natural stands. / Master of Science

The probability of mortality for an individual tree with certain characteristics growing under certain conditions was modeled. A particular algorithm SCREEN was used to fmd the best set of predictors variables. This algorithm was specially created to be used when the dependent variable can take only two values like in this binary case (dead or alive tree). The logistic model with different independent variables, which were found to be significant through the SCREEN algorithm, was fitted to the data. For the unthinned plots the logistic model with the following variables, CR (crown ratio), HH (total height/height of dominant and co-dominant trees) and CI (competition index) was compared with the survival model applied in a published distance-dependent model PTAEDA. The logistic model with CR, HH and DD (quadratic mean diameter/dbh) was compared with the survival model already used in a distance-independent model TRULOB. In both cases the behavior of the logistic model was quite similar to the published models. For the thinned plots the predictor variables DDt HH, CI and CR raised to 1.5 were used in the logistic model to predict mortality for individual trees. Mortality is difficult to predict. In this particular study the logistic model was used. The final distance-dependent model for unthinned plots includes as predictor variables CR, HH and CI. For thinned plots the final logistic model employs HH, CI and CR raised to 1.5 as independent variables. The final distance-independent model for unthinned plots includes as predictor variables HH, DD and CR. For thinned plots the final logistic model uses HH, DD and CR raised to 1.5 as independent variables. Differences between deterministic and the stochastic treatments of mortality were also studied. No practical differences in several stand characteristics such as average height, total volume, basal area were found when using these two approaches. Further, no significant differences were found in the diameter distribution for dead or alive trees. / Master of Science

The initial physiological processes leading to enhanced growth of loblolly pine subsequent to fertilization are not clearly understood. Much of the debate revolves around the temporal response of photosynthesis (Pn) to fertilization or even if Pn increases at all due to enhanced nutrition. This study tracked loblolly pine light-saturated photosynthesis (Asat), dark respiration (Rd), volume, height, basal diameter, and leaf area responses in eight clones to fertilization (112 kg/ha N) over the course of a growing season in the field. Measurements were conducted intensively before and after fertilization in order to track the initial physiological changes prior to any changes in growth in the fertilized seedlings. The results showed that fertilization does increase Pn rates although there was no significant effect on Rd rates during the study. The fertilized seedlings mean Asat rates were significantly higher on three sampling dates and remained higher throughout most of the sampling period. At the end of the growing season, the fertilized seedlings had a 30.5% higher projected crown area than the controls and 48% greater mean volumes. Physiological and growth responses were significantly different among clones with some showing large and others showing little or no response to fertilization. These results support the hypothesis from Gough et al. (2004b) that post-fertilization increases in Pn create extra photoassimilate used in building larger leaf areas. These larger leaf areas contribute to higher canopy photosynthesis levels, which leads to an increase in dry matter production. / Master of Science

The anatomical properties of loblolly pine (Pinus taeda L.) and cottonwood (Populus deltoides Barto ex. Marsh.), both from intensively managed woodlands, were quantitatively characterized using the principles of stereology. Physical and mechanical properties were also determined for each growth increment of six sample trees of both species. Anatomical parameters measured were correlated to certain mechanical properties. The numerical values obtained for the anatomical properties were derived from simple counting measurements. They included size distribution parameters of individual anatomical elements as viewed on transverse sections. The parameters were determined both in terms of within growth ring variability and in terms of changes from pith to bark within the species studied. Average mechanical properties of the two species were shown to increase significantly from pith to bark. In the regression models constructed for predicting physical and mechanical properties, up to three anatomical variables were found to significantly account for the variation in the strength properties. Close to 87% of the variation in MOR and 86% in MOE could be accounted for by the three anatomical parameters in loblolly pine. About 82% of the variation in the crushing strength parallel to grain could be explained by the anatomical variables. The three anatomical parameters selected for predicting strength properties in cottonwood were all related to fibers, suggesting that the most important anatomical elements determining strength in cottonwood are the fibers. Overall predictability in cottonwood was not as good as in loblolly pine. Less than 40% of the variation in MOR could be explained by fiber properties alone, while almost 70% in MOE was accounted for. Over 55% of the variation in maximum compression strength parallel to grain could be explained by fiber properties alone. About 84 to 94% of the variation in specific strength properties was accounted for by three anatomical variables unrelated to specific gravity in loblolly pine. Addition of specific gravity improved the model with R² values between 92-97%. In cottonwood, 65-85% of variation in specific strength properties was accounted for by three anatomical variables unrelated to specific gravity. The R² values also improved by addition of specific gravity (82-92%). / Ph. D.

Ph. D. / incomplete_metadata

Commercial thinning in the South is a highly efficient mechanized operation which operates year round. Southern winters are typically wet; therefore, the potential for soil rutting and compaction exists when heavy machines are used. This study was undertaken to determine if mechanized thinning in wet weather impacted the soils and affected tree growth. Soil and tree growth data were collected from two natural loblolly pine stands located in the coastal plain of Arkansas that were thinned 4-5 years previously. The Demonstration Area was 1.9 acres in size and 26 years old, with a site index of 50 feet (base age 25). The second study area, the Deer Camp Area, was 4.0 acres in size and 31 years old, with a site index of 60 feet (base age 25). The soil physical conditions in both study areas were not significantly impacted by the mechanized thinning operation. In general, the soils had bulk densities below 1.3 Mg/m³, approximately 15% macropore space, 30% micropore space, and ruts were generally less than 6 inches deep. Trees growing greater than 12 feet from the skidding corridors were compared with trees growing 0-12 feet from the skidding corridors. In both study areas, radial growth of the trees next to the corridors exceeded that of those between corridors after thinning. Other results varied by site. On the Demonstration Area the trees in the 0-12 foot zone had larger DBHs and crown widths than the trees between corridors; but the trees growing more than 12 feet from the corridor were taller than the trees growing within 12 feet of the corridor. In the Deer Camp Area, the trees within 12 feet of the corridor had larger DBHs, total heights, and heights to the live crown than the trees growing more than 12 feet from the corridor. The main reason tree growth next to the corridors exceeded that of trees between corridors ( > 12 feet from corridor) was because of heavier thinning in the areas closer to the corridor. The only post-thinning growth reductions were found in trees growing near the deepest ruts (i.e. >6 inches deep). In both study areas, these trees had extremely poor radial growth responses after the mechanized thinning, increasing only 1.6% in the Demonstration Area and decreasing 4.7% in the Deer Camp Area. The trees located on ruts less than 6 inches deep had the highest radial growth responses to the thinning operation. The trees on 3-6 inch ruts responded 20.2% in the Demonstration Area and 28.6% in the Deer Camp Area; on 0-3 inch deep ruts, the trees responded 15.0% and 23.3%, respectively. Bole damage was also found to reduce the growth of residual loblolly pine. Damaged trees growing within 6 feet of the rut had the lowest increase in radial growth after thinning. On both study areas, the damaged trees located more than 6 feet from the rut did not seem to be adversely affected by the bole damage. Overall, mature loblolly pine seems tolerant of small amounts of soil disturbance and basal damage, but, if both occur, then tree growth is severely reduced. / Master of Science