Browsing by Author "Burkhart, Harold E."

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    Agroforestry opportunities and constraints in the Água de Gato Watershed, Santiago, Cape Verde Islands
    Delgado, Orlando Jesus (Virginia Tech, 1996-08-23)
    The objectives of this study were to determine the opportunities, constraints, and willingness of the inhabitants and non-resident landowners to adopt a new land-use system in the Agua de Gato Watershed, to determine the degree of agroforestry technical support available to farmers in the watershed, and to determine suitable agroforestry systems which can be adapted to the watershed according to its biological and physical conditions. A random group of farmers of the Agua de Gato Watershed and a group of technicians working on the island of Santiago were interviewed in order to get individual and general information about the farms the and practice of agroforestry in the watershed. Only 56% of the technicians knew or had some knowledge about agroforestry, and the farmers think that they do not have enough technical support for better development of agriculture in the watershed. Although most of the farmers had a small piece of land, averaging 1.1 ha, most of them, 92%, were willing to adopt an agroforestry system as a new land use system for their farms.
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    Aids for Unit Planning on the Appalachian National Forests
    Burkhart, Harold E.; Leuschner, William A.; Stuck, R. Dean; Porter, John R.; Reynolds, Marion R. Jr. (Virginia Tech. Division of Forestry and Wildlife Resources, 1976)
    This report summarizes the results of studies conducted in response to a cooperative agreement between the Southern Region, U.S. Forest Service and the Department of Forestry and Forest Products, Virginia Polytechnic Institute and State University. The objective of the agreement was to improve National Forest management planning techniques. The agreement covered the period July 1, 1973 to June 30, 1975. Literature citations are given for those who desire additional detail.
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    An analysis of correlated curve trend experiments in Eucalyptus grandis
    Bredenkamp, Brian Victor (Virginia Polytechnic Institute and State University, 1988)
    Correlated curve trend (C.C.T.) experiments in Eucalyptus grandis on the Zululand coast of South Africa were analyzed. Growth parameters were described as functions of age using Schnute’s generalized growth function and parameter estimates were described as functions of stand density. Growth attributes were used as moments of a probability density function to describe a diameter distribution model for the species. Time trends in the relationships between growth parameters and stand density were scrutinized with multiple comparisons of paired means. It was shown that diameter growth in lower size classes ceases under conditions of extreme suppression while growth continues unabated in the larger size classes, resulting in greater dispersion in diameter. Competition mortality was to a large extent confined to the lower size classes and severe mortality results in an apparent increase in mean diameter which precludes use of growth functions which impose an asymptote. Allometric growth was investigated on two different sites and growth trends were shown to be anamorphic between sites. This permits a ratio approach to the estimation of growth and yield on one site based on experimental evidence from another. Thinning effects in terms of diameter and height changes were estimated from simulated thinnings using data from unthinned stands while the results of long-term thinning studies were compared in terms of cumulative volume yields. The age at which mean annual increment culminates was determined and a model for the estimation of m.a.i. as a function of age and stand density was constructed. A critical examination of spacing indices revealed that the slopes thereof were much steeper than those for many other species. The better-known indices of Reineke and Yoda were found to be dependent on age.
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    Analysis of timber harvest scheduling under alternative levels of land aggregation: an application to a hypothetical Mexican forest ownership
    Hernandez-Vazquez, Edgardo (Virginia Polytechnic Institute and State University, 1989)
    The problem of optimal land organization was approached via a general methodology to aggregate finely distinguished planning unit areas of an even-aged ponderosa pine forest in Northwestern Mexico. Factor analysis was applied to eighteen timber inventory variables to produce four independent and meaningful constructs that explained 87% of the total variable set’s variation. Next, each planning unit area was characterized by its factor scores and an Euclidean-metric based analysis was applied. The resultant Dendrograrn’s structure helped to define four levels of land aggregation that were evaluated with the same forest management policy. This policy simulated current Mexican forestry guidelines such as replacement stand’s regimes based on maximum mean annual increment, and area volume constraints for timber harvest scheduling. Then, the present value-maximizing timber harvest schedules for each level of land organization was found by using LP Model 1 formulations. Results showed that timber harvesting net benefits varied between 1.3% and 7.0% across levels of land aggregation. This fact was a consequence of the biophysical homogeneity of the forest and the Mexican assumptions of prices and flat costs for overhead and planning. Theoretical considerations indicated that if overhead and planning costs are properly considered for every level of land aggregation, the study’s methodology could show a greater present value difference between alternative levels of land organization.
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    Assessing Biotic and Abiotic Effects on Biodiversity Index Using Machine Learning
    Bayat, Mahmoud; Burkhart, Harold E.; Namiranian, Manouchehr; Hamidi, Seyedeh Kosar; Heidari, Sahar; Hassani, Majid (MDPI, 2021-04-10)
    Forest ecosystems play multiple important roles in meeting the habitat needs of different organisms and providing a variety of services to humans. Biodiversity is one of the structural features in dynamic and complex forest ecosystems. One of the most challenging issues in assessing forest ecosystems is understanding the relationship between biodiversity and environmental factors. The aim of this study was to investigate the effect of biotic and abiotic factors on tree diversity of Hyrcanian forests in northern Iran. For this purpose, we analyzed tree diversity in 8 forest sites in different locations from east to west of the Caspian Sea. 15,988 trees were measured in 655 circular permanent sample plots (0.1 ha). A combination of machine learning methods was used for modeling and investigating the relationship between tree diversity and biotic and abiotic factors. Machine learning models included generalized additive models (GAMs), support vector machine (SVM), random forest (RF) and K-nearest–neighbor (KNN). To determine the most important factors related to tree diversity we used from variables such as the average diameter at breast height (DBH) in the plot, basal area in largest trees (BAL), basal area (BA), number of trees per hectare, tree species, slope, aspect and elevation. A comparison of RMSEs, relative RMSEs, and the coefficients of determination of the different methods, showed that the random forest (RF) method resulted in the best models among all those tested. Based on the results of the RF method, elevation, BA and BAL were recognized as the most influential factors defining variation of tree diversity.
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    Assessing the utility of NAIP digital aerial photogrammetric point clouds for estimating canopy height of managed loblolly pine plantations in the southeastern United States
    Ritz, Alison L.; Thomas, Valerie A.; Wynne, Randolph H.; Green, P. Corey; Schroeder, Todd A.; Albaugh, Timothy J.; Burkhart, Harold E.; Carter, David R.; Cook, Rachel L.; Campoe, Otavio C.; Rubilar, Rafael A.; Rakestraw, Jim (Elsevier, 2022-09)
    Remote sensing offers many advantages to supplement traditional, ground-based forest measurements, such as limiting time in the field and fast spatial coverage. Data from airborne laser scanning (lidar) have provided accurate estimates of forest height, where, and when available. However, lidar is expensive to collect, and wall-to-wall coverage in the United States is lacking. Recent studies have investigated whether point clouds derived from digital aerial photogrammetry (DAP) can supplement lidar data for estimating forest height due to DAP's lower costs and more frequent acquisitions. We estimated forest heights using point clouds derived from the National Agricultural Imagery Program (NAIP) DAP program in the United States to create a predicted height map for managed loblolly pine stands. For 534 plots in Virginia and North Carolina, with stand age ranging from 1 year to 42 years old, field-collected canopy heights were regressed against the 90th percentile of heights derived from NAIP point clouds. Model performance was good, with an R2 of 0.93 and an RMSE of 1.44 m. However, heights in recent heavily thinned stands were consistently underestimated, likely due to between-row shadowing leading to a poor photogrammetric solution. The model was applied to non-thinned evergreen areas in Virginia, North Carolina, and Tennessee to produce a multi-state 5 m x 5 m canopy height map. NAIP-derived point clouds are a viable means of predicting canopy height in southern pine stands that have not been thinned recently.
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    Auxiliary information resolution effects on small area estimation in plantation forest inventory
    Green, P. Corey; Burkhart, Harold E.; Coulston, John W.; Radtke, Philip J.; Thomas, Valerie A. (2020-10)
    In forest inventory, traditional ground-based resource assessments are often expensive and time-consuming forcing managers to reduce sample sizes to meet budgetary and logistical constraints. Small area estimation (SAE) is a class of statistical estimators that uses a combination of traditional survey data and linearly related auxiliary information to improve estimate precision. These techniques have been shown to improve the precision of stand-level inventory estimates in loblolly pine plantations using lidar height percentiles and thinning status as covariates. In this study, the effects of reduced lidar point-cloud densities and lower digital elevation model (DEM) spatial resolutions were investigated for total planted volume estimates using area-level SAE models. In the managed Piedmont pine plantation conditions evaluated, lower lidar point-cloud densities and DEM spatial resolutions were found to have minimal effects on estimates and precision. The results of this study are promising to those interested in incorporating SAE methods into forest inventory programs.
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    Basal Area Growth and Crown Dynamics in a Loblolly Pine Spacing Trial
    Radtke, Philip J. (Virginia Tech, 1996-08-02)
    Relationships between the culmination of basal area growth and degree of crown closure in loblolly pine (Pinus taeda L.) were investigated. A spacing trial established on the low Appalachian Piedmont and Atlantic Coastal Plain provided the data for the investigation. Test plots were planted at densities ranging from 303 to 2723 stems per acre, and at various rectangular and square spacings. Annual stem and crown measurements were used to derive the sought-after relationships. The age of basal area culmination was found to be inversely related to both planting density and site index. Crown closure was advanced on sites of relatively high quality, exhibiting an approximately linear increase with time from planting until the age of basal area culmination. The slope of this trend increased with planting density. The degree of crown closure at the age of basal area culmination was significantly higher on narrowly-spaced plots than it was on widely-spaced plots; however, it did not vary significantly with site index. Although crown closure is generally accelerated on high quality sites, the relatively early culmination of basal area growth on such sites offsets the increase - the net result being that crown closure at culmination age does not vary significantly with site differences. Crown closure indices can be used to determine whether or not a stand has reached the culmination of basal area growth; however, more readily available information on spacing and site index can be used to make the same prediction. The results of this study might be most useful to modelers of early stand dynamics in loblolly pine and other commercially important pines.
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    Biomass Estimation Using the Component Ratio Method for White Oak
    DeYoung, Clara (Virginia Tech, 2014-08-26)
    With higher demands on biomass, the ability to accurately estimate the amount in a stand is more important now than ever before. Existing models currently in use by the Forest Inventory and Analysis (FIA) program of the United States Department of Agriculture (USDA) Forest Service include the Component Ratio Method (CRM). However, testing of the CRM models is needed to validate and calibrate them. The objective of this research was to test and develop a system of equations capable of producing consistent volume and biomass estimates for standing trees of commercially important hardwood species in the southeastern United States. Testing and comparing was done through use of new and legacy data to establish component ratios of trees and contrast these results to those from existing models. Specifically, analyses were completed for models of merchantable and whole stem volume, wood densities models and averages, and the component ratios for wood, bark, branches, and foliage. The existing models were then calibrated and adjusted. Results on accuracy and fitted results of updated models are reported, along with testing the effects of applying updated models over the state of Virginia.
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    Characterizing the Respiration of Stems and Roots of Three Hardwood Tree Species in the Great Smoky Mountains
    Rakonczay, Zoltán (Virginia Tech, 1997-06-16)
    Carbon dioxide efflux rates (CER) of stems and roots of overstory and understory black cherry (Prunus serotina Ehrh., BC), red maple (Acer rubrum L., RM) and northern red oak (Quercus rubra L., RO) trees were monitored over two growing seasons at two contrasting sites in the Great Smoky Mountains to investigate diurnal and seasonal patterns in respiration and to develop prediction models based on environmental and plant parameters. CER of small roots (d<0-8 mm) was measured with a newly developed system which allows periodic in situ measurements by using permanently installed flexible cuvettes. Temperature-adjusted CER of roots showed no diel variation. The moderate long-term changes occurred simultaneously in all species and size classes, suggesting that they were driven mostly by environmental factors. Mean root CER ranged from 0.5 to 4.0 nmol g⁻¹ d.w. s⁻¹. Rates were up to six times higher for fine roots (d<2.0 mm) than for coarse roots. CER (per unit length) of boles (d>10 cm) and twigs (d<2 cm) was related to diameter by the function lnCER = a+D·lnd, with D between 1.2 and 1.8. A new, scale-invariant measure of CER, based on D, facilitated comparisons across diameters. Q₁₀ varied with the method of determination, and it was higher in spring (1.8-2.5) than in autumn (1.4-1.5) for all species. Daytime bole CER often fell below temperature-based predictions, likely due to transpiration. The reduction (usually <10%) was less pronounced at the drier site. Twig CER showed more substantial (often >±50%) deviations from the predictions. Deviations were higher in the canopy than in the understory. Mean bole maintenance respiration (at 20°C and d=20 cm) was 0.66, 0.43 and 0.50 μMol m⁻¹, while the volume-based growth coefficient was around 5, 6 and 8 mol cm⁻³ for BC, RM and RO, respectively. In a controlled study, BC and RM seedlings were fumigated in open-top chambers with sub-ambient, ambient and twice-ambient levels of ozone. The twice-ambient treatment reduced stem CER in BC by 50% (p=0.05) in July, but there was no treatment effect in September or in RM. Ozone reduced root/shoot ratio and diameter growth in BC, and Pmax in both species.
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    Chemical interactions between rainfall and northern red oak (Quercus rubra l.) foliage
    Leininger, Theodor Daniel (Virginia Polytechnic Institute and State University, 1988)
    Nutrient ion exchange was examined between simulated acid rain solutions and northern red oak (Ouercus rubra L.) leaves of trees growing in fertile, limestone-derived soil and less fertile, sandstone/shale-derived soil. Leaves harvested from trees growing on the fertile site had greater concentrations of total N, P, K, Ca, and Mn but less total Mg than leaves of trees on the less fertile site. Cation losses from leaves of both sites were similar when exposed T3 to simulated rain solutions of pH 5.6, 4.3, and 3.0. Simulated rain solutions of pH 3.0 leached the greatest amount of total cations from leaves of both sites. Differences in acidity between leachates and starting rain solutions increased as the acidity of starting solutions contacting leaves of either site increased. Differences in leaf nutrient status between sites typically did not affect leachate acidity. Hydrogen ion exchange, believed to be the main mechanism of cation loss from leaves of both sites, accounted for 30 to 44% of all cations leached from leaves of both sites. Concentrations of inorganic ions were measured in bulk rainfall and bulk throughfall collected beneath northern red oak trees growing on the fertile and less fertile sites. Rainfall passing through crowns at both sites was enriched with S0₄²⁻, P0₄³⁻, Ca²⁺, Mg²⁺, K⁺, Mn²⁺, and Fe²⁺, but lost NH₄⁺ to the crowns. There was little difference in the inorganic chemistry of incident rainfall between sites. Large-particle dryfall ionic concentrations, rainfall volume, and leaf area were all larger at the fertile than at the less fertile site. Higher concentrations of Ca²⁺, Mg²⁺, NH₄⁺, Mn²⁺, and S0₄²⁻in throughfall at the fertile site compared to that of the less fertile site are likely due to the combination of these three factors. Historical northern red oak crown areas were estimated for the fertile and less fertile sites by a two step procedure using annual growth ring chronologies and published regression equations. These equations related total crown area to total crown dry weight. The usefulness of crown area estimates in throughfall studies was demonstrated by applying nutrient ion exchange data, collected beneath northern red oak crowns in 1984, to 1982 and 1930 crown area estimates. Smaller nutrient ion exchange estimates in 1930 were due to smaller crown area estimates.
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    Coarse Woody Debris in Industrially Managed Pinus taeda Plantations of the Southeastern United States
    Pittman, Judd R. (Virginia Tech, 2005-07-15)
    Coarse woody debris (CWD) plays an influential role in forested ecosystems by adding organic matter to soils, stabilizing the soil environment, providing wildlife habitat, preventing soil erosion, providing seedling establishment habitat, and involvement in the nutrient cycle. Most CWD research has been conducted in old-growth and unmanaged, second-growth forests. However, less is understood about CWD in intensively managed ecosystems, such as industrialized southern pine plantations. The objectives of this study were to determine the climatic and ecological factors that affect the decomposition rate of CWD, to predict the decomposition rate, specific gravity, and time since death (TSD) using multiple linear regression in industrial loblolly pine (Pinus taeda L.) plantations in the southeastern United States. The study sites for this project were part of a long-term, loblolly pine thinning study maintained by the Loblolly Pine Growth and Yield Research Cooperative at Virginia Tech. Measurements included piece size, position, and decay class. Samples of CWD were collected and analyzed to determine their mass and density. Decomposition rate of CWD was significantly different across position classes and decay classes: disk decomposition rates were significantly negatively correlated with disk diameter, large and small end piece diameter, estimated disk height, and disk dry weight. Average annual precipitation and average annual temperature were not significantly correlated with CWD disk decomposition rate.
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    A comparison of crown attributes for six genotypes on Pinus taeda as affected by site and management intensity
    Carbaugh, Eric Douglas (Virginia Tech, 2015-10-19)
    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.
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    A Comparison of Growth and Yield Prediction Models for Loblolly Pine
    Burkhart, Harold E.; Cao, Quang V.; Ware, Kenneth D. (Virginia Tech. Division of Forestry and Wildlife Resources, 1981)
    The objective of the study reported here was to analyze published growth and yield systems for loblolly pine, characterizing the nature of the data on which the study was based, specifying what input information is needed, and stating what output estimates and predictions are obtainable. Predicted values from various studies are also compared vis-a-vis those from other investigations, and, where possible, conclusions and recommendations are drawn.
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    Decision Support for Operational Plantation Forest Inventories through Auxiliary Information and Simulation
    Green, Patrick Corey (Virginia Tech, 2019-10-25)
    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.
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    A decisionmaking framework for assessing atmospheric deposition impacts on regional forest inventory
    Liu, Chiun-Ming (Virginia Polytechnic Institute and State University, 1988)
    A decisionmaking framework was developed to assess atmospheric deposition impacts on regional softwood inventory in Virginia. This decision making framework consists of three segments: a forest inventory projection model, a timber production function, and a timber consumption model. The Timber Resource Inventory Model (TRIM) was used to project future forest inventory, given initial inventory data, yield information, and harvest request. The timber production function allows the estimation of the individual effects of input variables on stand growth and yield. The timber consumption model was linked with TRIM to simulate the interactions between timber removals and inventory levels. Algorithm analysis, sensitivity analysis, and an a priori analysis were used to examine the feasibility of TRIM for projecting atmospheric deposition impacts on inventory. Modification of growth and harvest decision variables in TRIM allows this impact estimation. Schumacher's yield model was modified to develop the timber production function according to goodness-of-fit, minimal collinearity, and biological rationale. Crown length was used as a surrogate of a. biological factor to reflect atmospheric deposition impacts on stand growth and yield. The small variance inflation factor allows the crown length elasticity to serve as a measure of the quantitative effects on the yield table. A system of predictor equations was added to the yield equation for simulating stand dynamics. A consumption function approach was used to develop the timber removals model. The BoxCox transformation, the stepwise regression procedure, and standard error were used to select the functional form, predictor variables, and estimates for the timber removals model. This removals model was linked with TRIM for simulating the interactions between removals and inventory levels for Forest Industry and Other Private. The existing forecasts of removals based on Forest Service projections were used for impact estimation for all ownerships. This decisionmaking framework was applied to the softwood inventory data in Virginia to demonstrate the impact estimation. Sensitivity analysis showed that the percentage reduction of inventory and removals is directly related to the crown length reduction. The larger the crown length reduction, the greater the percentage reduction of the inventory. The percentage reduction of yield tables due to the crown length reduction is slightly less than the overall percentage reduction of the inventory but is slightly greater than the overall percentage reduction of removals. The quantitative information on atmospheric deposition impacts on crown variables is a key to the impact estimation for inventory and removals. Also, this decision making framework can be used to measure some silvicultural practice effects on regional inventory.
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    Determination of fertility rating (FR) in the 3-PG model for loblolly pine (Pinus taeda L.) plantations in the southeastern United States
    Subedi, Santosh (Virginia Tech, 2015-05-22)
    Soil fertility is an important component of forest ecosystem, yet evaluating soil fertility remains one of the least understood aspects of forest science. Phytocentric and geocenctric approaches were used to assess soil fertility in loblolly pine plantations throughout their geographic range in the United States. The model to assess soil fertility using a phytocentric approach was constructed using the relationship between site index and aboveground productivity. Geocentric models used physical and chemical properties of the A-horizon. Soil geocentric models were constructed using two modeling approaches. In the first approach, ordinary least squares methods of multiple regression were used to derive soil fertility estimated from site index using soil physical and chemical properties from the A-horizon. Ordinary least squares methods were found unsuitable due to multicollinearity among the soil variables. In the second approach, a multivariate modeling approach, partial least squares regression, was used to mitigate multicollinearity effects. The best model to quantify soil fertility using soil physical and chemical properties included N, Ca, Mg, C, and sand percentage as the significant predictors. The 3-PG process-based model was evaluated for simulating the response of loblolly pine to changes in soil fertility. Fertility rating (FR) is a parameter in 3-PG that scales soil fertility in the range of 0 to 1. FR values estimated from phytocentric and geocentric approaches were tested against observed production. The 3-PG model prediction of aboveground productivity described 89% percent of the variation in observed aboveground productivity using FR derived from site index and 84% percent of the vari- ation in observed aboveground productivity using FR derived from physical and chemical properties of the A-horizon. A response function to model dynamics of FR (∆FR) due to one time midrotatoin fertilization of N and P was developed using the Weibull function. The magnitude of ∆FR varied with intensity of N and time since application of fertilizer. The hypothesis that repeated fertilization with N and P eliminate major nutrient deficiency in the southeastern US was tested and a relationship between baseline fertility rating and fertilizer response was developed. An inverse relationship was observed between fertilizer response and baseline FR.
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    Development of a taper equation for Pinus oocarpa Schiede in natural stands of central Honduras
    Regalado, Darlin Noe Perez (Virginia Tech, 1988-06-05)
    Nine taper equations were tested to predict diameters inside bark along the stem for Pinus oocarpa Schiede trees growing in natural stands of central Honduras. A five parameter submodel predicted as well as an eight parameter model proposed by Kozak, 1988. Taper variation was explored between two geographic regions from which trees with different taper were suspected. Results showed that different site classes, not fully accounted for in the model, might have an effect on the prediction of taper in each region. Also, the effect of crown class and live crown ratio on prediction was evaluated. The model selected exhibited different prediction patterns for dominant and suppressed trees. On the other hand, live crown ratio did not appear to affect prediction. A computer program was written to use the taper equation developed to compute total and merchantable volume to different top diameter limits.
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    Diameter Distributions and Yields of Natural Stands of Loblolly Pine
    Burk, Thomas E.; Burkhart, Harold E. (Virginia Tech. Division of Forestry and Wildlife Resources, 1984)
    A diameter distribution yield model was developed based upon measurements of 117 0.1-acre temporary plots located in naturally regenerated loblolly pine stands in the Piedmont and Coastal Plain of Virginia and the Coastal Plain of North Carolina. Diameter distributions were derived using the Weibull density function by requiring that the distribution's arithmetic and quadratic means matched those predicted from stand-level attributes using regression equations. Software was written in FORTRAN and BASIC implementing the model and an existing basal area projection equation. Stand and stock tables are presented for 30-year projections from age 20 for various combinations of site index and initial basal area.
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    Diameter Distributions and Yields Of Thinned Loblolly Pine Plantations
    Cao, Quang V.; Burkhart, Harold E.; Lemin, Ronald C., Jr. (Virginia Tech. Division of Forestry and Wildlife Resources, 1982)
    A growth and yield model for thinned loblolly pine plantations was developed using data from 128 0.2-acre permanent plots in the Virginia Piedmont and Coastal Plain. The Weibull function, used to characterize stand diameter distributions, was searched to insure that the resulting total basal area and average dbh estimates were identical to those predicted from stand variables using regression equations. Program WTHIN was written in standard FORTRAN to provide stand and stock tables for thinned old-field loblolly pine plantations. Trials with different thinning intensities indicated reasonable trends, as compared with published studies.