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Browsing by Author "Burk, Thomas E."

Now showing 1 - 6 of 6
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    The combined effects of ozone, sulfur dioxide and simulated acid rain on the growth of three forest tree species
    Chappelka, Arthur H. (Virginia Polytechnic Institute and State University, 1986)
    Nine-week-old yellow-poplar and green and white ash were exposed to various concentrations of O₃ (0.00 to 0.15 ppm) and/or SO₂ (0.08 ppm), 4 hr/d, 5d/wk in combination with simulated rain (pHs 5.6, 4.3, 3.0), 1 hr/d, 2 d/wk, for 5 or 6 wk under controlled laboratory conditions. Pollutant exposures resulted in alterations in seedling biomass accumulation, growth rates, changes in carbon allocation among plant parts and modification in physiological processes associated with gas exchange. Ozone (0.010 ppm) and SO₂ together caused a significant decrease in height growth and biomass and an increase in leaf area ratio (LAR) in yellow-poplar. Ozone and SO₂ exposures resulted in linear decreases and increases, respectively, in root dry weight, leaf area increase, relative growth rates of all yellow-poplar plant parts and unit leaf rate with decreasing rain pH. Chlorophyll content increased in both O₃ and SO₂ treatments with increasing rain acidity. In green and white ash experiments height growth was inhibited by O₃, SO₂ and O₃ + SO₂ for green ash, whereas only leaf dry weight was decreased by O₃ exposure in white ash. Decreasing rain pH resulted in linear decreases in root/shoot ratio (RSR) and LAR, for white ash. In green ash, a quadratic response to rain pH occurred with these growth variables. Ozone and O₃ + SO₂-treated green ash exhibited a significant quadratic response in leaf weight ratio with increasing rain acidity. Leaf area ratio and RSR exhibited linear increases and decreases, respectively, for O₃ and rain acidity. In SO₂-treated white ash with increasing white ash and yellow-poplar seedlings exposed to various O₃ concentrations and simulated rain for 5 and 6 weeks, respectively, increasing O₃ concentrations caused linear decreases in height and biomass of white ash. Linear decreases in root growth rate and biomass and RSR occurred with decreasing rain pH, across O₃ treatments. Ozone (0.05 or 0.10 ppm) caused linear decreases in these variables in combination with increasing rain acidity. For yellow-poplar, increasing O₃ concentrations caused linear increases in RSR and specific leaf area. At 0.05 and 0.10 ppm O₃, stem and leaf biomass, their relative growth rates and leaf area all decreased with decreasing rain pH. Ozone (0.10 ppm) exposure caused a decrease in stomatal conductance, and decreasing variable. rain pH resulted in a linear decrease in this A linear decrease in net photosynthesis also occurred with increasing rain acidity in O₃-treated (0.10 ppm) plants. These results demonstrate that gaseous pollutants in combination with simulated acid rain can have detrimental effects on growth of three forest tree species, under controlled laboratory conditions.
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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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    Growth and Yield of Appalachian Mixed Hardwoods After Thinning
    Harrison, Wade C.; Burkhart, Harold E.; Burk, Thomas E.; Beck, Donald E. (Virginia Tech. Division of Forestry and Wildlife Resources, 1986)
    G-HAT (Growth of Hardwoods After Thinning) is a system of computer programs used to predict growth and yield of Appalachian mixed hardwoods after thinning. Given a tree list or stand table, along with inputs of stand age, site index, and stand basal area before thinning, G-HAT software uses species-specific individual tree equations to predict tree basal area increment and total height for the residual stand. Cubic foot volumes, based on desired merchantability standards, may be obtained for thinned trees, the residual stand, and the projected stand. G-HAT is available as a self-contained, interactive program (BASIC G-HAT) or as a library of FORTRAN subroutines (FORTRAN G-HAT). BASIC G-HAT, for personal computers, is designed for interactive, user-friendly sessions with keyboard input and screen output. Its use requires no programming ability. FORTRAN G-HAT is compatible with mainframe computers, minicomputers, and personal computers. It consists of modular subroutines which allow considerable flexibility in application, such as interface with computerized timber inventory systems and stand simulators.
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    Methods for modeling whole stem diameter growth and taper
    Newberry, James D. (Virginia Polytechnic Institute and State University, 1984)
    Stem profile models which allow for both taper and form changes (Gray 1956) were constructed and evaluated. Gray defined form to be the basic shape of the tree, e.g. cone or parabolid, and taper to be the rate of narrowing in diameter given a tree form. Ormerod's stem profile model was selected as the basic model since its parameters were readily interpretable in terms of Gray's taper and form definitions. Two stage modeling procedures were used to relate individual tree taper and form parameters to tree and stand characteristics. Two second-stage parameter estimation alternatives were evaluated. Parameter estimates for both techniques, ordinary least squares and random function analysis, were similar. Characteristics used to predict stem form were total tree height, crown ratio, height to the live crown, site index, and tree age. The taper parameter was related to diameter at breast height, crown ratio and site index. Error evaluations suggest that substantial gains in predicting stem diameters were not made using the variable taper and form stem profile models. Two methods were proposed for modeling whole stem inside-bark diameter or cross-sectional area increment. Whole stem increment models were derived from several stem profile models and Presseler's hypothesis on the vertical distribution of cross-sectional area growth. Stem profile models evaluated for constructing compatible increment models were Kozak and others (1969), Ormerod (1973), Goulding and Murray (1976), Max and Burkhart (1976), Cao and others (1980), and Amidon (1984). The increment model based on Presseler's hypothesis was derived as a generalization of the work of Mitchell (1975). Evaluations, with limited increment data, consistently showed that the models based on Presseler's hypothesis predict inside-bark diameter increment with less error than do the profile model compatible increment models. This may be due to the lack of crown information currently used in stem profile models.
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    Modeling growth dynamics of juvenile loblolly pine plantations
    Avila, Olga B. (Virginia Tech, 1993-09-14)
    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.
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    The spatial autocorrelation of individual tree characteristics in loblolly pine stands
    Reed, David Doss (Virginia Polytechnic Institute and State University, 1982)
    Mathematical methods of assessing the spatial autocorrelation associated with individual tree characteristics in forest stands were identified. These measures were used to investigate the spatial autocorrelation of discrete tree characteristics including the species, product, and defect classifications. With the exception of the species classification, none of the discrete tree characteristics examined showed any evidence of significant (α = 0.05) levels of spatial autocorrelation in loblolly pine stands. The significant autocorrelation of the species classification was probably due to past stand history or microsite variability rather than overall stand conditions such as age, density, or percent pine. The relationship between the level of spatial autocorrelation associated with basal area and several descriptive stand characteristics was also examined. No strong relationships were identified but trends were noticed between the autocorrelation measures and measures of stand competition such as basal area and crown competition factor. The measures of spatial association indicate positive autocorrelation between the characteristics of neighboring trees at very low levels of competition with the autocorrelation becoming increasingly negative as competition increases. At extremely high levels of competition, the spatial autocorrelation measures become positive again, reflecting the stagnated condition of the stand. Methods were developed, using the measures of spatial autocorrelation, to assign characteristics to individual trees in computer generated stands. These methods, applicable for discrete or continuous characteristics; assign the characteristics to individual trees depending on the spatial location of the individual tree and the locations and characteristics of its neighbors.