The Lower Coastal Plain of the southeastern United States is a major wood producing region. The region is characterized by a combination of nearly-level topography, poorly-drained soils, and high rainfall, which results in a perched water table in some soils that inundates the surface several times each year. Harvesting timber under wet site conditions often results in extensive soil compaction, rutting, soil displacement, and waterlogging. Forest managers are concerned that these visually-displeasing soil disturbances may cause site damage and reduced productivity. These concerns were addressed in an operational-scale field experiment conducted in South Carolina. The objectives of this experiment were to determine: (i) if soil disturbance changes key soil properties and processes; (ii) if soil disturbance reduces loblolly pine productivity; and, (iii) if disturbance can be mitigated with site preparation practices? Three 20-ha, 20-yr-old loblolly pine (Pinus taeda L.) plantations were harvested under wet and dry conditions to create a broad gradient in soil disturbance. Within each harvested plantation, a subset of 3-ha plots were site prepared by either bedding, or mole-plowing plus bedding, then all sites were established as 3rd -rotation pine plantations. Prior to site preparation, each plot was classified and mapped using a 5 by 5 soil disturbance (none to churned) by organic debris (none to slash piles) classification matrix. Within each plot, data were collected on several soil physical, chemical, and biological properties over a 2-yr period following site preparation. Key soil properties were integrated into a Soil Quality Index (SQI) and compared to aboveground productivity of 2-yr-old loblolly pine trees growing on closely-spaced (30 by 30 cm) bioassay plots planted across the gradient of soil disturbance. The soil physical properties were used to determine the least limiting water range (LLWR), the range in soil water content within which root growth is not limited. Soil compaction and deep rutting reduced the LLWR. Retention of logging slash improved the LLWR for compacted and rutted soils. Site preparation improved the quality of the soil physical environment across all levels of soil disturbance. Soil disturbance had no effect on soil chemical or biological properties as evidenced by no change in soil pH, ECEC, base saturation, available P, or net N mineralization with disturbance. The base saturation exceeded 80 % on all sites, with Ca saturation controlling soil pH. The high base saturation buffered any redox-induced changes in soil chemistry that would have resulted from disturbance. The results showed that high fertility is an important mechanism for buffering the potentially-negative effects of soil disturbance on the soil nutritional environment. Site preparation changed soil chemical properties, but the changes were probably associated with tillage effects on organic matter and clay content, not redox processes. The SQI showed that surface soil compaction and deep rutting reduced soil quality, mainly by decreasing the LLWR and aeration depth. Site preparation mitigated the effects of most disturbances on soil quality, evidenced by similar aboveground biomass production among soil disturbance classes after bedding. A regression model was developed for predicting aboveground biomass production as a function of SQI. SQI explained 73 % of the variation in aboveground biomass production. The regression model showed that compression tracks and rutting decreased aboveground biomass production compared to undisturbed soils. The long-term effect of these disturbances on productivity will depend on natural soil recovery processes. However, these early results suggest that compaction and rutting should be minimized on similar sites, especially if sites will not be bedded before reforestation. The mole-plow / bedding treatment increased aboveground biomass production, indicating that this experimental treatment may be a viable practice for enhancing productivity. / Ph. D.

A stochastic framework to simulate the process of initiation, diameter growth, death and self-pruning of branches in loblolly pine (Pinus taeda L.) trees was developed. A data set was obtained from a destructive sampling of whorl sections from 34 trees growing under different initial spacing. Data from dissected branches were used to develop a model for representing knot shape, which assumed that the live portion of a knot can be modeled by a one-parameter equation and the dead portion by assuming a cylindrical shape. For the developed knot model analytical expressions were derived for estimating the volume of knots (live/dead portions) for three types of branch conditions on simulated trees: (i) live branches, (ii) non-occluded dead branches, and (iii) occluded dead branches. This model was intended to recover information on knots shape and volume during the simulation process of branch dynamics. Three different components were modeled and hierarchically connected: whorl, branches and knots. For each new growing season, whorls and branches are assigned stochastically along and around the stem. Thereafter, branch diameter growth is predicted as function of relative location within the live crown and stem growth. Using a taper equation, the spatial location (X,Y,Z) of both live and dead portion of simulated knots is maintained in order to create a 3D representation of the internal stem structure. At the end of the projection period information on (i) vertical trend of branch diameter and location along and around the stem, (ii) volume of knots, and (iii) spatial location, size and type (live and dead) of knots can be obtained. The proposed branch model was linked to the individual-tree growth and yield model PTAEDA3.1 to evaluate the effect of initial spacing and thinning intensity on branch growth in sawtimber trees. The use of the dynamic branch model permitted generation of additional information on sawlog quality under different management regimes. The arithmetic mean diameter of the largest four branches, one from each radial quadrant of the log (i.e. Branch Index, BI) and the number of whorls per log were considered as indicators of sawlog quality. The developed framework makes it possible to include additional wood properties in the simulation system, allowing linkage with industrial conversion processes (e.g. sawing simulation). This integrated modeling system should promote further research to obtain necessary data on crown and branch dynamics to validate the overall performance of the proposed branch model and to improve its components. / Ph. D.

Informed forest management requires accurate, up-to-date information. Ground-based forest inventory is commonly conducted to generate estimates of forest characteristics with a predetermined level of statistical confidence. As the importance of monitoring forest resources has increased, budgetary and logistical constraints often limit the resources needed for precise estimates. In this research, the incorporation of ancillary information in planted loblolly pine (Pinus taeda L.) forest inventory was investigated. Additionally, a simulation study using synthetic populations provided the basis for investigating the effects of plot and stand-level inventory aggregations on predictions and projections of future forest conditions. Forest regeneration surveys are important for assessing conditions immediately after plantation establishment. An unmanned aircraft system was evaluated for its ability to capture imagery that could be used to automate seedling counting using two computer vision approaches. The imagery was found to be unreliable for consistent detection in the conditions evaluated. Following establishment, conditions are assessed throughout the lifespan of forest plantations. Using small area estimation (SAE) methods, the incorporation of light detection and ranging (lidar) and thinning status improved the precision of inventory estimates compared with ground data alone. Further investigation found that reduced density lidar point clouds and lower resolution elevation models could be used to generate estimates with similar increases in precision. Individual tree detection estimates of stand density were found to provide minimal improvements in estimation precision when incorporated into the SAE models. Plot and stand level inventory aggregations were found to provide similar estimates of future conditions in simulated stands without high levels of spatial heterogeneity. Significant differences were noted when spatial heterogeneity was high. Model form was found to have a more significant effect on the observed differences than plot size or thinning status. The results of this research are of interest to forest managers who regularly conduct forest inventories and generate estimates of future stand conditions. The incorporation of auxiliary data in mid-rotation stands using SAE techniques improved estimate precision in most cases. Further, guidance on strategies for using this information for predicting future conditions is provided. / Doctor of Philosophy / Informed forest management requires accurate, up-to-date information. Groundbased sampling (inventory) is commonly used to generate estimates of forest characteristics such as total wood volume, stem density per unit area, heights, and regeneration survival. As the importance of assessing forest resources has increased, resources are often not available to conduct proper assessments. In this research, the incorporation of ancillary information in planted loblolly pine (Pinus taeda L.) forest inventory was investigated. Additionally, a simulation study investigated the effects of two forest inventory data aggregation methods on predictions and projections of future forest conditions. Forest regeneration surveys are important for assessing conditions immediately after tree planting. An unmanned aircraft system was evaluated for its ability to capture imagery that could be used to automate seedling counting. The imagery was found to be unreliable for use in accurately detecting seedlings in the conditions evaluated. Following establishment, forest conditions are assessed at additional points in forest development. Using a class of statistical estimators known as small-area estimation, a combination of ground and light detection and ranging data generated more confident estimates of forest conditions. Further investigation found that more coarse ancillary information can be used with similar confidence in the conditions evaluated. Forest inventory data are used to generate estimates of future conditions needed for management decisions. The final component of this research found that there are significant differences between two inventory data aggregation strategies when forest conditions are highly spatially variable. The results of this research are of interest to forest managers who regularly assess forest resources with inventories and models. The incorporation of ancillary information has potential to enhance forest resource assessments. Further, managers have guidance on strategies for using this information for estimating future conditions.

The controversy regarding commercial thinning continues to intensify as pine plantation acreage in the south increases. This controversy has caused industrial and nonindustrial landowners to re-examine the economic returns from their plantation investments. This study was undertaken to develop investment guidelines for the management of loblolly pine plantations. Computer simulation was used to evaluate the effect on present value that four future price/market scenarios, three management regimes, and three mechanized thinning systems can have on current thinning investments. When the economic returns from thinning are compared with a no-thin management regime, simulation results indicate that long-term investment advantages favor thinning only slightly, regardless of the future price/market scenario assumed. This slight difference suggests that individual forest product companies may find other reasons such as wood flow, tax advantages, and future product requirements of their manufacturing facilities to be overriding factors for engaging in commercial thinning. Generally, short-run cost and production differences between thinning systems are more significant than the long-term investment effects. Consequently, the type of mechanized thinning system employed has a negligible impact on the total investment. / Ph. D.

Studies were conducted to determine the incidence and severity of Heterobasidion annosum (Fr.) Bref. root rot in loblolly pine (Pinus taeda L.) unthinned plantations and subsoiled seed orchards and to demonstrate the potential for direct root colonization by percolated basidiospores. Twenty-two 0.02 ha circular plots were installed in nine unthinned loblolly pine plantations in Virginia. Five plantations were located on sites classified as high hazard for annosum root rot while four plantations were located on low hazard sites. Bulldozer excavation of the root systems permitted extensive analysis of annosum root rot incidence and severity which was substantiated by isolation of the asexual stage of the fungus from symptomatic resinous and stringy-decayed roots. On low hazard sites, 10 of 300 trees (3.3 percent) were colonized by H. annosum with 2 trees (0.7 percent) severely colonized ( > 1 percent of the total root system mass). On high hazard sites, 29 of 348 trees (8.3 percent) were colonized with 5 trees (1.4 percent) severely colonized. On low hazard sites, the predominant colonization symptom was stringy decay which indicated an older established disease situation as opposed to colonized trees on high hazard sites which exhibited resin-soaking characteristic of more recent infection and colonization. No basidiocarps were observed on any trees on low hazard plots while only 2 trees exhibited conks on high hazard sites. Mean radial increment growth differences between H. annosumcolonized and noncolonized trees were analyzed using the Duncan's Multiple Range test and for the 10-year period prior to excavation no significant growth reduction was observed. Due to low incidence and severity of annosum root rot in unthinned loblolly pine plantations and the absence of reduced radial increment growth, the disease is not a primary management consideration, especially on low hazard sites. However, the disease may be of secondary importance in managing first-generation unthinned loblolly pine plantations on high hazard sites due to inoculum production from residual stumps of H. annosum trees removed during thinning. The root systems of 2, 20 and 30 loblolly pines at the Chesapeake Corporation, Virginia Division of Forestry and Union Camp Corporation seed orchards, respectively, were excavated with a backhoe to permit intensive analysis of subsoiled roots for annosum root rot incidence and severity. The absence of wound callus, lack of adventitious root formation and the presence of a resin-soaked band greater than approximately 6 mm wide at the wound surface were three criteria for determining whether a lateral primary root had failed to heal following subsoiling. Soil texture was closely associated with the incidence and severity of general root disease as the wetter soil conditions at the Chesapeake Corporation seed orchard probably afforded a more amenable environment for the healing of subsoiled roots. Sandy, drought-susceptible soils at the Union Camp Corporation and Virginia Division of Forestry seed orchards were associated with the higher incidence and severity of root disease among subsoiled lateral primary roots. The asexual stage of H. annosum was not successfully isolated from resin soaked subsoiled root tissue at any of the three orchards. Duncan's Multiple Range analysis demonstrated that mean radial increment growth was significantly decreased among healthy and declining subsoiled trees at the three orchards. At the Union Camp Corporation orchard, when healthy and declining trees were subsoiled they exhibited significantly less radial increment growth than their respective control counterparts. Loblolly pine root segments were inoculated with a suspension of H. annosum basidiospores and observed using scanning electron microscopy. Appressorial-like structures occurred at distal ends of elongated germ tubes demonstrating probable direct infection of loblolly pine root segments. / Ph. D.

Understory forage production, species composition, and nutrient concentrations were studied in relation to overstory structure and site characteristics in thinned loblolly pine (Pinus taeda) plantations in the Virginia Piedmont. Stands exhibited a wide range in overstory basal areas (18.8 to 43.5 m²/ha) and site indices (14.2 to 23.8 m at base age 25 years). Understory forage production for the 0 to 2 m stratum averaged 610 kg/ha and ranged from 154 to 1690 kg/ha. Initially, differential models were used to develop prediction equations relating understory production to overstory characteristics, but an empirical prediction equation proved to be somewhat superior. Forage production was most predictable from total overstory basal area, canopy cover, and slope position. Understory species composition was analyzed with respect to overstory structural and site gradients, using vegetation ordination techniques. Species composition was less closely related to these gradients than was production; however, the greatest species diversity appeared to occur during the period following thinning but before crown closure, when successional and mid-tolerant species coexisted. Nutrient concentrations in forage material averaged 4643 cal/g for gross energy, 38.3 percent for invitro dry matter digestibility by white-tailed deer (Odoooiteus virginiana) and 8.4 percent for crude protein. There were no apparent trends of these nutrient concentrations with respect to overstory structural or site characteristics. Forage based carrying capacities for white-tailed deer were computed using values from this study for production and nutrient concentrations, and values from the literature for deer forage preferences and nutrient requirements. Results indicated that the pine habitat could support 0.03 to 0.19 lactating does per ha during the summer season, and that energy and not protein is likely the limiting nutritive parameter. Suggestions are made for future research in pine overstory-understory and wildlife habitat relationships. These include the use of experimental overstory manipulation followed by periodic remeasurements to directly observe changes in understory production and species composition, intensive sampling to determine specific local wildlife forage preferences, and the quantification of wildlife movements and population dynamics. / Ph. D.

The objective of this study was to develop diameter/basal area increment equations for loblolly pine trees in thinned and unthinned plantations on cutover, site-prepared areas. Results indicated that one set of coefficients was sufficient to estimate individual tree growth (for the three year period following thinning) on lightly thinned and heavily thinned plots. However, unthinned plots required a separate set of coefficients and therefore a separate equation to estimate growth. Diameter growth was adequately explained by some form of the following regressor variables: pine basal area, hardwood basal area, initial age, initial diameter, average height of the dominant and codominant trees, and crown ratio ( optional). Transforming the dependent variable from a function of diameter to a similar function of basal area had no apparent effect on the precision of the predicted results. Two alternative methods of predicting diameter growth were evaluated: (1) direct fitting of diameter growth, and (2) fitting a potential diameter growth equation and a modifier function. Even though the potential times modifier approach performed slightly better in terms of fitting the data, it provided unrealistic results at ages beyond the upper range of the data. After additional data are obtained at older ages, the potential times modifier approach may surpass the direct approach. However, at present, the direct diameter growth model was chosen as the final model form. / M.S.

A loblolly pine phosphorus fertilization trial was evaluated 20 years after establishment on a Tatum silt loam in the Virginia Piedmont. Triple superphosphate (TSP) was applied at 160 kg P/ha and ground rock phosphate (GRP) was applied at both 160 kg P/ha and 670 kg P/ha. Lime (4.48 T/ha) was applied with and without the TSP treatment. Tree growth was not significantly affected by treatment and foliar phosphorus levels were above 0.10% indicating that a deficiency was not the immediate growth limiting factor. Double-acid-extractable soil phosphorus critical levels established for the Coastal Plain do not appear useful for diagnosing tree requirements for this Piedmont soil. A critical level of 1.0 ppm double-acid-extractable phosphorus would be more applicable to this soil. GRP was more effective than TSP after 20 years at increasing phosphorus uptake, probably due to a slower dissolution rate and the inclusion of F-ions which reacted with soil Al to reduce phosphorus fixation. Although an increase in the A horizon pH persisted for 20 years, there was no increase in phosphorus uptake as a direct response to this higher pH. Liming may have some long-term merit when applied in conjunction with a water soluble phosphorus fertilizer such as TSP by reducing the transformations of applied phosphorus to unavailable forms. / Master of Science

Field and greenhouse studies were conducted to investigate the role of water stress and time of glyphosate spraying in the variation in glyphosate efficacy. Data on water potential, foliar sugar and starch content, weather, and growth response were gathered for loblolly pine and four of its major competitors on 16 operationally sprayed tracts in Virginia. Glyphosate successfully released loblolly pine on all tracts. Control of white oaks was significantly related to foliar sugar concentration. Water potential and weather variables were not related to glyphosate efficacy for any species. Seedlings of loblolly pine, red maple, and sweetgum were raised in a greenhouse and nursery environment. At the end of the second growing season, three water stress treatments were imposed on each species at each of four glyphosate application dates. ¹⁴C-glyphosate was applied to a subsample of seedlings. Timing of application. water stress, or both significantly affected susceptibility of all three species to glyphosate. Efficacy for all three species corresponded to that expected from field data. Differences in species susceptibility to glyphosate were explained by differences in ¹⁴C-glyphosate translocation, but there was no difference among species in absorption of glyphosate. Efficacy changes across application dates followed seasonal changes in foliar sugar concentration. / Master of Science

Crown structure for 9- to 30-year-old loblolly pine was quantified via analysis of branch diameters and location, both along and around the bole, using observational data from 68 trees. The trees analyzed ranged in size from 11.1 to 31.6 cm in DBH and from 8.30 to 25.67 m in height, and were growing in Piedmont and Atlantic Coastal Plain stands ranging from 70 to 200 sq. ft. BA/acre. A series of equations was used to describe the diameter distribution of branches. Circular statistics were used to examine branching patterns around the bole. A recursive system of 2 equations was developed in order to predict the total number of branches within a crown. A series of 3 equations was used to describe the average of and range in diameter within a whorl. Attempts at modeling the height above ground to branches (whorls) were unsuccessful; therefore, equidistant spacing was assumed. Similarly, predicting the number of branches within a whorl of a certain height was difficult, and overall percentages were employed. Analysis of branch azimuths on a whole tree basis indicated a uniform distribution was appropriate (and not a “circular normal” distribution). Finally circular correlation was used to analyze rotational patterns within and between whorls, and a strong positive correlation was found for consecutive whorls of the same number of branches. From this study it was concluded that modeling crown structure will be difficult, with much variation occurring among trees. More data are necessary to better refine the baseline work herein presented. / Master of Science