Browsing by Author "Fox, Thomas R."
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- Analysis of a lidar voxel-derived vertical profile at the plot and individual tree scales for the estimation of forest canopy layer characteristicsSumnall, Matthew; Peduzzi, Alicia; Fox, Thomas R.; Wynne, Randolph H.; Thomas, Valerie A. (2016)The goal of the current study was to develop methods of estimating the height of vertical components within plantation coniferous forest using airborne discrete multiple return lidar. In the summer of 2008, airborne lidar and field data were acquired for Loblolly pine forest locations in North Carolina and Virginia, USA, which comprised a variety of stand conditions (e.g. stand age, nutrient regime, and stem density). The methods here implement both field plot-scale analysis and an automated approach for the delineation of individual tree crown (ITC) locations and horizontal extents through a marker-based region growing process applied to a lidar derived canopy height model. The estimation of vertical features was accomplished through aggregating lidar return height measurements into vertical height bins, of a given horizontal extent (plot or ITC), creating a vertical 'stack' of bins describing the frequency of returns by height. Once height bins were created the resulting vertical distributions were smoothed with a regression curve-line function and canopy layers were identified through the detection of local maxima and minima. Estimates from Lorey's mean canopy height was estimated from plot-level curve-fitting with an overall accuracy of 5.9% coefficient of variation (CV) and the coefficient of determination (R-2) value of 0.93. Estimates of height to the living canopy produced an overall R-2 value of 0.91 (11.0% CV). The presence of vertical features within the sub-canopy component of the fitted vertical function also corresponded to areas of known understory presence and absence. Estimates from ITC data were averaged to the plot level. Estimates of field Lorey's mean canopy top height from average ITC data produced an R-2 value of 0.96 (7.9% CV). Average ITC estimates of height to the living canopy produced the closest correspondence to the field data, producing an R-2 value of 0.97 (6.2% CV). These results were similar to estimates produced by a statistical regression method, where R-2 values were 0.99 (2.4% CV) and 0.98 (4.9% CV) for plot average top canopy height and height to the living canopy, respectively. These results indicate that the characteristics of the dominant canopy can be estimated accurately using airborne lidar without the development of regression models, in a variety of intensively managed coniferous stand conditions.
- An Analysis of Log Truck Turn Times at Harvest Sites and Mill FacilitiesDowling, Tripp N. (Virginia Tech, 2010-04-19)The raw forest products transportation sector is inherently unique when compared to other transportation industries. The loggers and contractors who transport raw forest products are at a competitive disadvantage. Older equipment is also commonly used by the raw forest products transportation industry in harsh working environments. The average log truck age is 9.7 years while all trucks average only 3.9 years. Nineteen percent of log trucks are 15 years old or older while only 5.9% of all trucks are older than 8 years. Log trucks are regulated by both the Federal Motor Carrier Safety Administration and the state that the truck operates in, thus making interstate transportation more difficult. In addition to these challenges, there is a lack of information concerning efficiency and productivity improvement opportunities related to transporting forest products. This study evaluated truck turn times at both the harvesting site and mill facilities in order to identify important trucking productivity factors and efficiency improvement opportunities. Regression equations were created to estimate truck turn times at harvesting sites and mill facilities. Gross level studies found that 1268 truck turns at the tract scale averaged 1.40 hours while 576 truck turns at the mill scale averaged 0.56 hours. Elemental time studies at four harvesting locations found that log trucks were idle 32% of the time. Trucks spent 29% of time being loaded and 26% of the time waiting. Elemental time studies at mill facilities found that trucks were idle 27% of the time. Trucks spent the greatest amount of time unloading while unbinding was the second greatest contributor to turn times. Reductions in loading and waiting times can have significant effects on the overall turn time. Harvesting contractors could benefit from maintaining balanced harvesting crews. Estimates indicate that harvesting contractors could earn an additional profit of $106,500 over a period of five years by purchasing an additional skidder for those crews whose production is limited due to a lack of skidding capacity. It is estimated that if adding an additional trailer to harvesting crews would allow an additional 2 loads to be transported to the mill each day, harvesting crews could earn an additional $22,100 per year of profit. Road construction can also affect harvesting contractors profits. By minimizing road construction through the use of easements and improved pre-harvest planning, harvesting contractors could reduce road construction costs by as much as $14,000 per tract. With tools available to estimate truck turn around times, harvesting contractors, fleet managers, and truck drivers will be able to make more informed decisions regarding fleet management. This will enable those owning and operating trucks to operate in more efficient and profitable manners. The models created during this study will allow managers to estimate tract and mill turn times so as to better allocate trucking resources.
- Assessing the transferability of statistical predictive models for leaf area index between two airborne discrete return LiDAR sensor designs within multiple intensely managed Loblolly pine forest locations in the south-eastern USASumnall, Matthew; Peduzzi, Alicia; Fox, Thomas R.; Wynne, Randolph H.; Thomas, Valerie A.; Cook, Bruce (2016-04)Leaf area is an important forest structural variable which serves as the primary means of mass and energy exchange within vegetated ecosystems. The objective of the current study was to determine if leaf area index (LAI) could be estimated accurately and consistently in five intensively managed pine plantation forests using two multiple-return airborne LiDAR datasets. Field measurements of LAI were made using the LiCOR LAI2000 and LAI2200 instruments within 116 plots were established of varying size and within a variety of stand conditions (i.e. stand age, nutrient regime and stem density) in North Carolina and Virginia in 2008 and 2013. A number of common LiDAR return height and intensity distribution metrics were calculated (e.g. average return height), in addition to ten indices, with two additional variants, utilized in the surrounding literature which have been used to estimate LAI and fractional cover, were calculated from return heights and intensity, for each plot extent. Each of the indices was assessed for correlation with each other, and was used as independent variables in linear regression analysis with field LAI as the dependent variable. All LiDAR derived metrics were also entered into a forward stepwise linear regression. The results from each of the indices varied from an R-2 of 0.33 (S.E. 0.87) to 0.89 (S.E. 0.36). Those indices calculated using ratios of all returns produced the strongest correlations, such as the Above and Below Ratio Index (ABRI) and Laser Penetration Index 1 ( LPI1). The regression model produced from a combination of three metrics did not improve correlations greatly (R-2 0.90; S.E. 0.35). The results indicate that LAI can be predicted over a range of intensively managed pine plantation forest environments accurately when using different LiDAR sensor designs. Those indices which incorporated counts of specific return numbers (e.g. first returns) or return intensity correlated poorly with field measurements. There were disparities between the number of different types of returns and intensity values when comparing the results from two LiDAR sensors, indicating that predictive models developed using such metrics are not transferable between datasets with different acquisition parameters. Each of the indices were significantly correlated with one another, with one exception (LAI proxy), in particular those indices calculated from all returns, which indicates similarities in information content for those indices. It can then be argued that LiDAR indices have reached a similar stage in development to those calculated from optical-spectral sensors, but which offer a number of advantages, such as the reduction or removal of saturation issues in areas of high biomass.
- Belowground Carbon and Nitrogen Cycling in a Loblolly Pine Forest Managed for Bioenergy ProductionMinick, Kevan J. (Virginia Tech, 2014-10-21)Concern over rising atmospheric CO2 due to fossil fuel combustion has intensified research into carbon-neutral energy and fuel production. Therefore, bioenergy production has expanded during the last decade, increasing demand for forest-based bioenergy feedstocks. Millions of acres of privately and industrially owned pine plantations exist across the southeastern US, representing a vast area of land that could be utilized to produce bioenergy without significant land-use change or diversion of agricultural resources from food production. Furthermore, loblolly pine (Pinus taeda L.) plantations offer the unique opportunity to utilize space between rows of planted trees to grow an herbaceous bioenergy crop, such as switchgrass (Panicum virgatum L.). This novel forest management regime has the potential to provide positive environmental and economic services, but hinges in part on impacts to soil carbon (C) and nitrogen (N) cycling, availability of belowground resources, and potential negative impacts of competition between pine and switchgrass on plant productivity. Three specific objectives were addressed in this study: 1) compare different bioenergy management regimes in regards to temporal dynamics of N cycling and availability following forest establishment (see Chapter 2); 2) determine the impact of loblolly pine and switchgrass intercropping on microbial N cycling processes (see Chapter 3); and 3) evaluate chemical and physical mechanisms of soil organic matter (SOM) stabilization and test their sensitivity to pine-switchgrass intercropping (see Chapter 4). The study site was located in the Lower Coastal Plain physiographic province in Lenoir County, North Carolina, USA (35-12'59'' N; 077-26'13'' W). Soils were mapped as Pantego (fine‐loamy, siliceous, semiactive, thermic Umbric Paleaquults) or Rains (fine‐loamy, siliceous, semiactive, thermic Typic Paleaquults) soil series, both of which are very poorly drained. However, previous site management in the late 1960’s and early 1970’s included installation of ditches to lower the water table and reduce saturation at the soil surface. Additionally, bedding of soil in rows was used to raise root systems of planted loblolly pine seedlings above the water table, increase soil aeration, and reduce competition. Space between bedded rows of pine trees was referred to as the interbed. Results from Chapter 2 showed that switchgrass significantly reduced interbed soil NH4 + and NO3 - concentrations by 39% and 60%, respectively, over the course of the timeframe (30 months) of this study. Surprisingly, in beds of the pine-switchgrass treatment significant increases in NO3 - concentration were measured from July - December 2011. From Chapter 3, gross N mineralization rates ranged from 0.18 - 4.7 µg N g -1 soil d-1 , while gross nitrification rates ranged from 0.02 - 0.47 µg N g-1 soil d-1 . At the 0-5 cm depth in switchgrass interbeds, gross N mineralization was reduced from April to November potentially reflecting microbial C limitations due to reduced soil C concentrations. At the 0-5 cm depth in beds of the pine-switchgrass treatment, gross N mineralization rates were elevated by 1.29 µg N iii g -1 soil d-1 in November and 1.02 µg N g-1 soil d-1 in February on average corresponding to a 305% and 193% increase, respectively. From Chapter 4, total C content in beds and interbeds ranged from 15 to 88 Mg C ha-1 and was reduced by 27% in beds of the pine-switchgrass treatment. Average C concentration for aggregate fractions was significantly lower in beds of the pine-switchgrass treatment at 0-5, 15- 30, and 30-45 cm depths, amounting to ~23%, ~28%, and ~34% reduction, respectively. Values of δ 13C for the >2000 µm aggregate size fraction at the 0-5 cm depth were diluted, corresponding to estimates of 13 - 25% of the >2000 µm C pool comprised of new pine-derived C. For SOM fractionated by density, elevated C concentrations were found in the occluded light fractions in both beds and interbeds of the pine-switchgrass treatment. Enriched δ13C in occluded light fractions led to estimates of 2.5 - 12.5% of this C fraction comprised of new switchgrass-derived C. In the free light fraction, new pine-derived C accounted for 15% and 9% of C at the 5-15 and 15-30 cm depth, respectively. Three overarching conclusions were generated from my research: 1) switchgrass grown between loblolly pine trees effectively utilized excess soil NH4 + and NO3 - when N availability was high following harvesting of a mature plantation proceeded by establishment of a second rotation of loblolly pine (see Chapter 2); 2) gross N mineralization rates were reduced under switchgrass during the growing season when soil C availability was low, but were elevated under switchgrass and adjacent loblolly pines when switchgrass was dormant and C availability was likely higher (see Chapter 3); and 3) SOM stabilized by physical or chemical mechanisms responded differently to pine-switchgrass intercropping, with losses in aggregate-stabilized C and gains in occluded, mineral-stabilized C. Furthermore, losses of aggregate C was associated with a significant reduction in total soil C in beds of the pine-switchgrass treatment. Results from 13C mass balance suggested incorporation of switchgrass-derived C into occluded light fractions of beds and interbeds. Finally, incorporation of new pine-derived C into the >2000 µm aggregate size fraction and free light fraction indicate pine inputs of particulate organic matter into these SOM fractions in beds of the pine-switchgrass treatment (see Chapter 4). I hypothesize that loblolly pines have increased root growth in beds in response to competition with switchgrass for N in the interbed, thereby alleviating seasonal microbial C limitations and stimulating microbial N cycling processes and increasing plant-available N. Overall, this research suggests that soil C and N cycling in pine plantations is altered by intercropping of pine and switchgrass. Through a mechanistic understanding of how C and N are cycled in forests and the impact of various forest management regimes on soil C and N cycling, effective management strategies can be implemented to utilize forests for intensive biomass production while limiting loss of soil C and N, and in some cases even enhancing soil C and N retention. Future research initiatives should seek to unravel the complex belowground interactions between roots of different plant species and soil microbial communities competing for limiting resources. Understanding how these interactions drive soil C storage, N cycling and availability, and forest productivity will ultimately improve resource utilization in these managed ecosystems as well as our basic understanding of how natural and managed ecosystems function.
- Beyond Finding Change: multitemporal Landsat for forest monitoring and managementWynne, Randolph H.; Thomas, Valerie A.; Brooks, Evan B.; Coulston, J. O.; Derwin, Jill M.; Liknes, Greg C.; Yang, Z.; Fox, Thomas R.; Ghannam, S.; Abbott, A. Lynn; House, M. N.; Saxena, R.; Watson, Layne T.; Gopalakrishnan, Ranjith (2017-07)Take homes
- Tobler’s Law still in effect with time series – spatial autocorrelation in temporal coherence can help in both preprocessing and estimation
- Continual process improvement in extant algorithms needed
- Need additional means by which variations within (parameterization) and across algorithms addressed (the Reverend…)
- Time series improving higher order products (example with NLCD TCC) enabling near continuous monitoring
- Biogeochemistry of Carbon on Disturbed Forest LandscapesAmichev, Beyhan Y. (Virginia Tech, 2007-04-11)Carbon accreditation of forest development projects is essential for sequestering atmospheric CO2 under the provisions of the Kyoto Protocol. The carbon sequestration potential of surface coal-mined lands is not well known. The purpose of this work was to determine how to measure carbon sequestration and estimate the additional amount that could be sequestered using different reforestation methods compared to the common practice of establishing grasslands. I developed a thermal oxidation technique for differentiating sequestered soil carbon from inorganic and fossilized carbon found at high levels in mine soils along with a geospatial and statistical protocol for carbon monitoring and accounting. I used existing tree, litter, and soil carbon data for 14 mined and 8 adjacent, non-mined forests in the Midwestern and Eastern coal regions to determine, and model sequestered carbon across the spectrum of site index and stand age in pine, mixed, and hardwood forest stands. Finally, I developed the framework of a decision support system consisting of the first iteration of a dynamic model to predict carbon sequestration for a 60-year period for three forest types (white pine, hybrid poplar, and native hardwoods) at three levels of management intensity: low (weed control), medium (weed control and tillage) and high (weed control, tillage, and fertilization). On average, the highest amount of ecosystem carbon on mined land was sequestered by pine stands (148 Mg ha-1), followed by hardwood (130 Mg ha-1) and mixed stands (118 Mg ha-1). Non-mined hardwood stands contained 210 Mg C ha-1, which was about 62% higher than the average of all mined stands. After 60 years, the net carbon in ecosystem components, wood products, and landfills ranged from 20 to 235 Mg ha-1 among all scenarios. The highest net amount of carbon was estimated under mixed hardwood vegetation established by the highest intensity treatment. Under this scenario, a surface-mined land of average site quality would sequester net carbon stock at 235 Mg C ha-1, at a rate of 3.9 Mg C ha-1 yr-1, which was 100% greater than a grassland scenario. Reforestation is a logical choice for mined land reclamation if carbon sequestration is a management objective.
- Changes in Soil Nitrogen Following Biosolids Application to Loblolly Pine (Pinus Taeda L.) Forest in the Virginia PiedmontArellano Ogaz, Eduardo (Virginia Tech, 2009-01-12)Application of biosolids as an alternative source of Nitrogen (N) is becoming a common silviculture practices on loblolly pine forest. However, little is known about how biosolids type, application rate, and timing affect forest floor and soil N availability in pine plantations. The objectives of this study were to determine the effect of different types, rates, and season of application of biosolids on forest floor and soil N. The study was established in a 17-year-old loblolly pine plantation in Amelia County, VA. Anaerobically digested (AD225), lime stabilized (LS225), and pelletized (Pellet225) biosolids and a conventional inorganic urea plus diammonium phosphate fertilizer (U+DAP225) were surface applied at a rate of 225 kg ha-1 based on Plant Available Nitrogen (PAN) between March 5th and 10th, 2006. Anaerobically digested biosolids were also surface applied at the rates of 900 kg PAN ha-1 and 1800 kg PAN ha-
- Chemistry and Transport of Metals from Entrenched Biosolids at a Reclaimed Mineral Sands Mining Site in Dinwiddie County, VirginiaLasley, Katrina (Virginia Tech, 2008-06-30)Deep row incorporation of biosolids is an alternative land application method that may allow higher than currently permitted mine land reclamation application rates. Biosolids treated by various processes possess characteristics that uniquely affect metal solubility and mobility due to their influence on metal speciation. The objectives of this research were to compare the effects of biosolids stabilization type and rate on heavy metal solubility, mobility, and speciation. Two rates each of Alexandria, (Virginia) anaerobically digested (213 and 426 dry Mg ha-1) and Blue Plains (Washington, DC) lime-stabilized (329 and 657 dry Mg ha-1) biosolids were placed in trenches at a mineral sands mine reclamation site in Dinwiddie County, Virginia in June and July 2006. Vertical and lateral transport of heavy metals from the biosolids seams were determined by analyzing leachate collected in zero tension lysimeters below the trenches and suction lysimeters adjacent to the trenches. Chloride (Cl-), sulfate (SO42-), nitrate (NO3-), phosphate (PO43-), dissolved organic carbon (DOC), and pH were also determined within the dissolved fractions (< 0.45 µm) collected on September 8, 2006, November 3, 2006, January 5, 2007, June 8, 2007, and September 7, 2007 as input for the speciation program MINTEQA2. Silver, Cd, Pb, and Sn did not move vertically or laterally to any significant extent. Lime-stabilized biosolids produced higher cumulative metal mass transport per sampling period for Cu (967 g ha-1), Ni (171 g ha-1), and Zn (1027 g ha-1) than the anaerobically digested biosolids and control during the 15-month period following entrenching. Barium mass loss was similar for both biosolids. All metals moved primarily with particulates. MINTEQA2 predicted the majority of the metals within the dissolved fraction were present as free ions. As pH decreased and time increased, the amount of association with fulvic acids decreased allowing more free ions and binding with inorganic ligands. Little movement into groundwater demonstrates that anaerobically digested and lime-stabilized biosolids can be land-applied at high rates with little concern of heavy metal contamination of groundwater under these conditions.
- A common garden experiment examining light use efficiency and heat sum to explain growth differences in native and exotic Pinus taedaAlbaugh, Timothy J.; Fox, Thomas R.; Maier, Christopher A.; Campoe, Otavio C.; Rubilar, Rafael A.; Cook, Rachel L.; Raymond, Jay E.; Alvares, Clayton A.; Stape, Jose L. (2018-10-01)Previous work indicates that Pinus taeda L. grows faster and has a higher carrying capacity when grown outside its native range. We were interested in examining the hypotheses that growth, light use efficiency (volume growth and absorbed photosynthetically active radiation relationship, LUE) and volume growth per unit heat sum is the same for native and exotic plantations. To test these hypotheses, we installed a common garden experiment where the same six genetic entries of P. taeda (four clonal varieties, one open pollinated family and one control mass pollinated family) were planted at three densities (618, 1235, and 1853 stems ha(-1)) with three or four replications at three sites (Virginia (VA), and North Carolina (NC) in the United States and Parana State in Brazil (BR)). The VA and BR sites were outside the native range of P. taeda. After five years of growth, the BR site had larger trees and stand scale basal area and volume were increasing faster than the other sites. Site did not affect LUE but density and genetic entry did. The sites were at different latitudes but the average photosynthetically active radiation at the top of the canopy was similar for the years when all sites were operational, likely because the BR site receives more rain annually and the cloudiness associated with the rain may have reduced available light. We estimated an hourly heat sum where the daytime temperature was between 5 and 38 degrees C, hours where vapor pressure deficit exceeded 1.5 kPa and days following nights where nighttime temperatures were less than 0 degrees C were excluded. Site was significant for the cumulative volume and heat sum relationship, for a given level of cumulative degree hours the sites ranked BR > VA > NC in cumulative volume. The different growth per unit of degree hours for each site indicated that something other than the heat sum was causing the observed difference in growth. Other factors including respiration and extreme climatic conditions may contribute to growth differences per unit degree hour and including these differences in the analysis would require a more detailed modeling effort to examine. The sites used in this study are ideally suited to continue testing additional hypotheses to explain the different growth between native and exotic P. taeda plantations because they have the same genotypes at all sites and consequently eliminate differences in genetics as a potential explanation for observed growth differences.
- A Comparison of Chipper Productivity, Chip Characteristics, and Nutrient Removals from Two Woody Biomass Harvesting TreatmentsGroover, Miles Clark (Virginia Tech, 2011-11-30)Increased costs of fossil fuels, regulatory policies, and investments by federal and state governments have caused increased interest and incentive for the use of wood as a renewable form of energy. As a result, landowners and forest managers are considering chipping whole trees and harvesting residues as a means to meet increased demand of wood chips as a renewable source of energy. However, the profitability, productivity gains, and sustainability of these alternative harvesting methods continue to be an area of research. The objective of this study was to compare two biomass harvesting treatments with regard to the characteristics of the chips they produced, chipper productivity, nutrient removals, and site disturbance. The first biomass harvesting treatment was an integrated harvest where roundwood was merchandized and hauled to the appropriate mill and limbs, tops, and small stems (residues) were chipped for hog fuel. The second biomass harvesting treatment simulated a scenario where biomass markets were competing with pulpwood markets and landowners could choose to sell wood for energy or pulp wood. In this treatment whole trees and small stems were chipped for hog fuel. A third harvesting treatment was a conventional roundwood harvest where no wood was chipped, and this treatment was used as a control for comparison of nutrient removals and site disturbance. The chips produced from both harvesting treatments were very similar, but those produced from whole trees tended to be slightly smaller than those produced from residues. Chipper productivity was significantly higher when chipping whole trees and it was also much more efficient in terms of fuel use. Estimations of nutrient removals showed that there was very little difference in the amount of nutrient removed from the biomass harvesting treatments, but both treatments removed significantly more N and Ca than the conventional roundwood harvesting treatment. There was significantly more downed and standing material left on the site after harvesting in the conventional treatment, but this did not translate into a large amount of additional nutrients left on the site. There was little difference in soil disturbance between all three treatments, and due to the dry soil conditions during harvesting, there was very little visual soil disturbance at all during harvesting.
- A comparison of crown attributes for six genotypes on Pinus taeda as affected by site and management intensityCarbaugh, 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.
- Complementarity increases production in genetic mixture of loblolly pine (Pinus taeda L.) throughout planted rangeCarter, David R.; Albaugh, Timothy J.; Camo, Otávio C.; Grossman, Jake J.; Rubilar, Rafael A.; Sumnall, Matthew; Maier, Christopher A.; Cook, Rachel L.; Fox, Thomas R. (ESA, 2020-09-01)Increased genotypic diversity has been associated with increased biomass production in shortrotation tree species. Increasing the genotypic diversity of loblolly pine (Pinus taeda L.) in an attempt to increase productivity has not been extensively studied nor tested operationally or over long durations (i.e., >7 yr). We used genetically mixed and pure rows of loblolly pine growing throughout its planted range— Virginia, North Carolina, and Brazil—to test the effects of genetic mixing on volume production. There were no significant effects of mixing rows compared to pure rows on uniformity or mortality. Under intensive silviculture, individual trees planted in mixed rows had approximately 7% greater volume than those in the pure rows (estimate = 0.015 m³/tree ± 0.006) in the final year of measurement—year 8 for Brazil and year 10 for North Carolina and Virginia. Scaling the increase in individual stem volume under mixed rows and intensive silviculture to 1235 stems ha⁻¹ would equate to an additional 1.85 m³∙ha⁻¹∙yr⁻¹ in mean annual increment. Measuring the net biodiversity effect, our data suggest the positive growth response is driven by complementarity and not selection, meaning both genetic entries tend to grow larger when grown together. Additional trials are necessary to test the effects of mixing rows across large plots and to assess whether this increase is sustained throughout the rotation. If this increasing trend were to hold for intensively managed plantations, strategically mixing rows to increase productivity could be a valuable addition to an intensively managed plantation requiring relatively little added operational consideration to implement.
- Creating Landscape-Scale Site Index Maps for the Southeastern US Is Possible with Airborne LiDAR and Landsat ImageryGopalakrishnan, Ranjith; Kauffman, Jobriath S.; Fagan, Matthew E.; Coulston, John W.; Thomas, Valerie A.; Wynne, Randolph H.; Fox, Thomas R.; Quirino, Valquiria F. (MDPI, 2019-03-06)Sustainable forest management is hugely dependent on high-quality estimates of forest site productivity, but it is challenging to generate productivity maps over large areas. We present a method for generating site index (a measure of such forest productivity) maps for plantation loblolly pine (Pinus taeda L.) forests over large areas in the southeastern United States by combining airborne laser scanning (ALS) data from disparate acquisitions and Landsat-based estimates of forest age. For predicting canopy heights, a linear regression model was developed using ALS data and field measurements from the Forest Inventory and Analysis (FIA) program of the US Forest Service (n = 211 plots). The model was strong (R2 = 0.84, RMSE = 1.85 m), and applicable over a large area (~208,000 sq. km). To estimate the site index, we combined the ALS estimated heights with Landsat-derived maps of stand age and planted pine area. The estimated bias was low (−0.28 m) and the RMSE (3.8 m, relative RMSE: 19.7%, base age 25 years) was consistent with other similar approaches. Due to Landsat-related constraints, our methodology is valid only for relatively young pine plantations established after 1984. We generated 30 m resolution site index maps over a large area (~832 sq. km). The site index distribution had a median value of 19.4 m, the 5th percentile value of 13.0 m and the 95th percentile value of 23.3 m. Further, using a watershed level analysis, we ranked these regions by their estimated productivity. These results demonstrate the potential and value of remote sensing based large-area site index maps.
- Crown architecture, crown leaf area distribution, and individual tree growth efficiency vary across site, genetic entry, and planting densityAlbaugh, Timothy J.; Maier, Christopher A.; Campoe, Otavio C.; Yanez, Marco A.; Carbaugh, Eric D.; Carter, David R.; Cook, Rachel L.; Rubilar, Rafael A.; Fox, Thomas R. (2020-02)We examined crown architecture and within crown leaf area distribution effects on Pinus taeda L. growth in North Carolina (NC), Virginia (VA), and Brazil (BR) to better understand why P. taeda can grow much better in Brazil than in the southeastern United States. The NC, VA, and BR sites were planted in 2009, 2009, and 2011, respectively. At all sites, we planted the same two genetic entries at 618, 1236, and 1854 trees ha(-1). In 2013, when trees were still open grown, the VA and NC sites had greater branch diameter (24%), branch number (14%), live crown length (44%), foliage mass (82%), and branch mass (91%), than the BR site. However, in 2017, after crown closure and when there was no significant difference in tree size, site did not significantly affect these crown variables. In 2013, site significantly affected absolute leaf area distribution, likely due to differences in live crown length and leaf area, such that there was more foliage at a given level in the crown at the VA and NC sites than at the BR site. In 2017, site was still a significant factor explaining leaf area distribution, although at this point, with crown closure and similar sized trees, there was more foliage at the BR site at a given level in the crown compared to the VA and NC sites. In 2013 and 2017, when including site, genetic entry, stand density, and leaf area distribution parameters as independent variables, site significantly affected individual tree growth efficiency, indicating that something other than leaf area distribution was influencing the site effect. Better BR P. taeda growth is likely due to a combination of factors, including leaf area distribution, crown architecture, and other factors that have been identified as influencing the site effect (heat sum), indicating that future work should include a modeling analysis to examine all known contributing factors.
- Determination of fertility rating (FR) in the 3-PG model for loblolly pine (Pinus taeda L.) plantations in the southeastern United StatesSubedi, 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.
- Determination of Fertility Rating (FR) in the 3-PG Model for Loblolly Pine Plantations in the Southeastern United States Based on Site IndexSubedi, Santosh; Fox, Thomas R.; Wynne, Randolph H. (MDPI, 2015-08-28)Soil fertility is an important component of forest ecosystems, yet evaluating soil fertility remains one of the least understood aspects of forest science. We hypothesized that the fertility rating (FR) used in the model 3-PG could be predicted from site index (SI) for loblolly pine in the southeastern US and then developed a method to predict FR from SI to test this hypothesis. Our results indicate that FR values derived from SI when used in 3-PG explain 89% of the variation in loblolly pine yield. The USDA SSURGO dataset contains SI values for loblolly pine for the major soil series in most of the counties in the southeastern US. The potential of using SI from SSURGO data to predict regional productivity of loblolly pine was assessed by comparing SI values from SSURGO with field inventory data in the study sites. When the 3-PG model was used with FR values derived using SI values from SSURGO database to predict loblolly pine productivity across the broader regions, the model provided realistic outputs of loblolly pine productivity. The results of this study show that FR values can be estimated from SI and used in 3-PG to predict loblolly pine productivity in the southeastern US.
- Diagnosis of Loblolly Pine (Pinus taeda L.) Nutrient Deficiencies by Foliar MethodsSypert, Robert Hall (Virginia Tech, 2006-08-18)Quick identification of loblolly pine nutrient deficiencies has troubled foresters who wish to increase productivity through fertilization. In the past, extensive field trials were established that did not allow for quick identification of a large number of possibly limiting nutrients in individual stands. This study used single-tree fertilization with macro-nutrients (N, P, K, Ca, Mg, S) and micro-nutrients (Mn, Zn, B, Cu, Fe, Mo) to identify deficiencies using foliar techniques in one growing season. Four study sites in TX, AL, GA, and SC were established in loblolly pine plantations at or near canopy closure. Nutrient concentrations relative to the critical level, optimal nutrient ratios, DRIS methodology, vector analysis, and changes in individual fascicle and total current year foliage weight/area were used to identify deficiencies. Phosphorus was repeatedly indicated as most limiting growth at TX while K was implicated at SC. The GA site revealed multiple deficiencies including N, K, and S. The AL site revealed only a very suspect B deficiency. Critical level methodology was effective in identifying deficiencies of N, P, and K, while B, S, and Cu appeared to be available at sufficient quantities when concentrations were below the published critical levels. Concentrations of S were especially below the critical levels and not increased by fertilization indicating that the critical levels were too high. Nutrient ratio interpretability was reduced by luxury uptake of N in comparison to other deficient nutrients. DRIS methodology was hampered by the inability to create effective comparative norms. Deficiency detection with vector analysis created problems when B and Mn displayed greater uptake relative to controls than the macro-nutrients that provided relative foliage mass increases. Resulting diagnosis indicated deficiencies when B and Mn were really taken up as luxury consumption. Vector analysis may not be as effective as its individual parts. Foliage weight/area responses detected fewer deficiencies than the other techniques. No significant foliar responses were seen at the TX or AL sites. However, K at the SC site was identified as deficient by all foliage mass variables, and multiple deficiencies were detectable at the GA site.
- Diversity, Invasibility, and Stability of Appalachian Forests across an Experimental Disturbance GradientBelote, R. T. (Virginia Tech, 2008-09-05)For this dissertation, I measured how plant communities in Appalachian forests responded to disturbances caused by forest management activities. I had two primary objectives including (1) testing theories of biological diversity and invasions by nonnative species; and (2) providing empirical data that will help guide the sustainable use of forest resources. This work is part of the Southern Appalachian Silviculture and Biodiversity (SASAB) experiment that was established in the early 1990s to investigate ecosystem responses to a gradient of timber harvesting disturbances. Ranging from undisturbed controls to silvicultural clearcuts, the disturbance gradient is replicated at sites located throughout the Appalachian mountains of Virginia and West Virginia. The plant community was sampled across a wide range of spatial scales (2 hectares to 1 m2) using a nested sampling design and was also sampled at three times including pre-disturbance, one year post-disturbance, and ten year post-disturbance. For one element of the study I tested modern theories of biological invasions and investigated how the forest disturbance gradient interacted with species diversity to influence invasion by nonnative species (Chapter 2). Contrary to popular ecological theories of biotic resistance, the most diverse sites tended to be more easily invaded following intense canopy disturbance. Interestingly, none of the sites in this study were dominated by invasive plants, which led me to ask whether dominant tree species in forests provided resistance to nonnative plant establishment and growth through the quality of the litter they produce. I also asked how might animals that are known to alter litter layers interact with dominant tree species to influence plant invasions. Therefore, I conducted an experiment investigating how changes in litter from dominant tree species and invasions by nonnative earthworms might influence invasibility of forests using forest floor mesocosms (Chapter 3). I found that plant invasion was inhibited by native oak litter even when earthworms were present, suggesting that oak forests may resist plant invasions via oak tree litter. In contrast, plant invasion was greater under invasive tree litter and earthworm activity tended to facilitate invasive plant success only under invasive tree litter. I was also interested in understanding how disturbance might alter relationships between local and regional diversity. The long-term data of the forest disturbance experiment allowed me to investigate how local species richness is mediated by regional species richness after disturbance and during forest community development (Chapter 4). Local richness depended strongly on regional richness only after disturbance via colonization of species, but this relationship changed during forest aggradation. These results suggest that regional species pools are important to maintain local diversity following disturbance, but that local interactions (through canopy closure of dominant trees) exert control over species diversity during community reorganization. Lastly, I tested current theories on how diversity influences compositional stability after disturbance (Chapter 5). Disturbance consistently resulted in decreased compositional stability, but diversity was associated with stability in complex ways, which depended on how stability was measured and at what scale. Species-rich areas were in some instances less stable; in other instances areas with intermediate levels of diversity were more stable. These results suggest that disturbance causes shifts in species composition via colonization, but the ways in which diversity of sites influences compositional stability is complex and depends on methods used and the scales of observation. Taken together, these results suggest that disturbance influences invasibility, species saturation, and compositional stability of ecological communities. These properties change immediately following disturbance, and during forest development and canopy closure. Data from this project were useful in testing existing theories of community ecology, and may ultimately prove useful for forest managers as they decide how to protect biodiversity while planning for other uses of forest resources. Overall, these results suggest that colonization of species is the primary process driving plant community patterns in Appalachian forests following disturbance.
- Ecology of Root-Feeding Insect Assemblages in Fire-Manipulated Longleaf Pine-Wiregrass EcosystemsDittler, Matthew Jason (Virginia Tech, 2013-05-23)Root-feeding insects can have top-down influence on vegetative composition and ecosystem processes; however, they may respond to bottom-up factors such as soil resources, site productivity, and disturbance. My research addressed the following questions: (1) Do disturbance (fire), vegetative composition, soil resources, and fine root standing mass influence the structure of root-feeding insect assemblages? (2) What types of roots do root-feeding insects eat, and do they forage selectively? (3) Do root-feeding insects influence fine root productivity? To address these questions, I studied root-feeding insect assemblages in longleaf pine wiregrass (Pinus palustris-Aristida stricta) ecosystems of southwestern Georgia, U.S.A. On a random basis, study sites were burned at least every other year (B), or left unburned (UB) for about 9 years. Fine root productivity and root-feeding insect abundances were sampled repeatedly across 54 random plots in UB and B sites. In Chapter 2, I characterized spatial and temporal patterns of root-feeding insect abundance, understory plant composition, soil resource availability, and fine root standing mass within each plot. Insect population densities were low overall, but abundance, patchiness, and diversity were greater in UB sites. Abundance patterns were significantly related to vegetative composition. In Chapter 3, I quantified the diet of root-feeding insects by measuring the natural abundance of carbon (C) and nitrogen (N) stable isotopes in insects and fine roots. Using 13C abundance, I examined the contribution of warm season grass roots to insect diet, relative to the proportion of warm season grass roots within adjacent root standing crop samples; 15N abundance was used to detect omnivory. Overall, insects appeared to be non-selective herbivores and omnivores that may alter foraging behavior to maintain a mixed diet (i.e. reducing or increasing warm season grass consumption when its abundance was high or low, respectively). The extent of omnivory varied within and among taxa. In Chapter 4, I estimated the top-down influence of root-feeding insects on fine root productivity by comparison of ingrowth cores with or without an insecticide treatment. I detected a weak positive effect of herbivores on the productivity of non-grass fine roots (< 10% of fine root productivity).
- Effects of a Control Release Nitrogen Fertilizer and Thinning on the Nitrogen Dynamics of a Mid-Rotation Loblolly Pine Stand in the Piedmont of VirginiaElliot, James Robertson (Virginia Tech, 2006-12-15)Nitrogen deficiency is characteristic of many mid-rotation loblolly pine (Pinus taeda L.) plantations in the Piedmont region of the southeastern USA. Fertilization with urea is the most common method used to correct this deficiency. Previous studies show that urea fertilization produces a rapid pulse of available nitrogen (N) with only a portion being utilized by plantation trees. Controlled release fertilizers release available N more slowly over a longer period of time and therefore may result in greater uptake efficiency. The objective of this study was to compare Nitroform®, a urea-formaldehyde controlled release N fertilizer versus urea and a control by measuring the effects of the two fertilizer treatments on N availability and loss as: total KCl extractable-N, total ion exchange membrane-N (IEM-N), N mineralization, and N volatilization, in a mid-rotation loblolly pine plantation in the Piedmont of Virginia. In addition, mid-summer and mid-winter fertilizations were compared to assess fertilizer uptake as a function of season. After the summer fertilization, Nitroform® significantly increased total KCl-extractable N, IEM-N, and N mineralization for two to three months over urea and the control. Three hundred times more N volatilized from urea than from controlled release Nitroform®. Interestingly, seven months after the summer application, the controlled release Nitroform® showed marked immobilization for three months while urea demonstrated greater N mineralization. After the winter application, fertilization with urea demonstrated greater soil inorganic N concentrations for two to three months over Nitroform®, very little N was immobilized, and volatilization was only 10 times that of Nitroform®. After summer and winter fertilizations, both fertilizer treatments significantly increased soil inorganic N concentrations and N volatilization over controls, however did not significantly increase N mineralization over controls when average response was tested over the entire sampling period. In addition to the fertilizer effects measured, a thinning only treatment was also incorporated into this study with soil N-availability indices compared to a control with no thinning or fertilization. The results from the thinning only treatment demonstrated no significant increases over the control in total KCl extractable-N, IEM-N, N-mineralization, or N volatilization when average responses were tested over the entire sampling period.