Browsing by Author "Seiler, John R."
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- An Adaptive Computer Vision Technique for Estimating the Biomass and Density of Loblolly Pine Plantations using Digital Orthophotography and LiDAR ImageryBortolot, Zachary Jared (Virginia Tech, 2004-04-23)Forests have been proposed as a means of reducing atmospheric carbon dioxide levels due to their ability to store carbon as biomass. To quantify the amount of atmospheric carbon sequestered by forests, biomass and density estimates are often needed. This study develops, implements, and tests an individual tree-based algorithm for obtaining forest density and biomass using orthophotographs and small footprint LiDAR imagery. It was designed to work with a range of forests and image types without modification, which is accomplished by using generic properties of trees found in many types of images. Multiple parameters are employed to determine how these generic properties are used. To set these parameters, training data is used in conjunction with an optimization algorithm (a modified Nelder-Mead simplex algorithm or a genetic algorithm). The training data consist of small images in which density and biomass are known. A first test of this technique was performed using 25 circular plots (radius = 15 m) placed in young pine plantations in central Virginia, together with false color othophotograph (spatial resolution = 0.5 m) or small footprint LiDAR (interpolated to 0.5 m) imagery. The highest density prediction accuracies (r2 up to 0.88, RMSE as low as 83 trees / ha) were found for runs where photointerpreted densities were used for training and testing. For tests run using density measurements made on the ground, accuracies were consistency higher for orthophotograph-based results than for LiDAR-based results, and were higher for trees with DBH ≥10cm than for trees with DBH ≥7 cm. Biomass estimates obtained by the algorithm using LiDAR imagery had a lower RMSE (as low as 15.6 t / ha) than most comparable studies. The correlations between the actual and predicted values (r2 up to 0.64) were lower than comparable studies, but were generally highly significant (p ≤ 0.05 or 0.01). In all runs there was no obvious relationship between accuracy and the amount of training data used, but the algorithm was sensitive to which training and testing data were selected. Methods were evaluated for combining predictions made using different parameter sets obtained after training using identical data. It was found that averaging the predictions produced improved results. After training using density estimates from the human photointerpreter, 89% of the trees located by the algorithm corresponded to trees found by the human photointerpreter. A comparison of the two optimization techniques found them to be comparable in speed and effectiveness.
- Analysis of Dryland Forest Phenology using Fused Landsat and MODIS Satellite ImageryWalker, Jessica (Virginia Tech, 2012-09-07)This dissertation investigated the practicality and expediency of applying remote sensing data fusion products to the analysis of dryland vegetation phenology. The objective of the first study was to verify the quality of the output products of the spatial and temporal adaptive reflectance fusion method (STARFM) over the dryland Arizona study site. Synthetic 30 m resolution images were generated from Landsat-5 Thematic Mapper (TM) data and a range of 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance datasets and assessed via correlation analysis with temporally coincident Landsat-5 imagery. The accuracy of the results (0.61 < R2 < 0.94) justified subsequent use of STARFM data in this environment, particularly when the imagery were generated from Nadir Bi-directional Reflectance Factor (BRDF)-Adjusted Reflectance (NBAR) MODIS datasets. The primary objective of the second study was to assess whether synthetic Landsat data could contribute meaningful information to the phenological analyses of a range of dryland vegetation classes. Start-of-season (SOS) and date of peak greenness phenology metrics were calculated for each STARFM and MODIS pixel on the basis of enhanced vegetation index (EVI) and normalized difference vegetation index (NDVI) time series over a single growing season. The variability of each metric was calculated for all STARFM pixels within 500 m MODIS extents. Colorado Plateau Pinyon Juniper displayed high amounts of temporal and spatial variability that justified the use of STARFM data, while the benefit to the remaining classes depended on the specific vegetation index and phenology metric. The third study expanded the STARFM time series to five years (2005-2009) to examine the influence of site characteristics and climatic conditions on dryland ponderosa pine (Pinus ponderosa) forest phenological patterns. The results showed that elevation and slope controlled the variability of peak timing across years, with lower elevations and shallower slopes linked to higher levels of variability. During drought conditions, the number of site variables that controlled the timing and variability of vegetation peak increased.
- Applying the diagnosis and recommendation integrated system(DRIS) to Fraser fir Christmas treesKopp, Virginia Ann (Virginia Tech, 1988-05-15)The process of diagnosing the foliar nutrient status of Fraser fir [Abies fraseri (Pursh)Poir.] Christmas trees and prescribing fertilizers is not well understood. Agricultural researchers have established critical yield levels for agronomic crops that are objective measures of crop quality and have associated these yields with nutrient status; however, Christmas tree quality is subjective and not well associated with nutrient status. A nutrient-sensitive tree response factor that reflects tree quality is needed for a proper diagnosis. The purpose of this study was to determine the relationship between nutrient balance and indices of tree quality and to evaluate how nutrient balance and tree quality can be manipulated by fertilizer inputs based on the Diagnosis and Recommendation Integrated System. In 1984 a factorial N, P, pH, fertilizer source, and fertilizer frequency trial was installed in northwestern North Carolina. A randomized complete block design with factorial combinations of all five factors was used. After three years, the fertilizer trial was analyzed to study the effects of fertilizer additions on foliar nutrient balance and tree quality. Several tree response factors were measured in the fall after dormancy. Statistical methods such as correlations and multivariate discriminant analysis were used to determine which response factors were correlated with foliar nutrients and which factor most governed tree quality. DRIS indices were calculated for six independent plots of different fertility treatments. Basal diameter (BD) was the strongest discriminator of tree quality and was used as a substitute for yield in the DRIS analyses. The importance of nutrient intensity was demonstrated since significant nutrient / dry matter ratios were calculated for N, P, K, and Mg. Balance was shown to be important since the indices for N, K, and Mg were a function of the four other nutrient ratios other than dry matter, and the P and Ca indices were a function of three nutrient ratios other than dry matter. Nutrient balance was also shown to be important by the significant relationship of BD as a function of the nutrient balance index (NBI). When NBI had a relatively small value, large BD trees were produced; as NBI values increased, BD decreased. Fertilizer additions that created nutrient imbalances also decreased BD, in spite of the high nutrient intensities found in the foliage. These results show that nutrient balance in Fraser fir foliage, as well as nutrient intensity, is important for producing optimal Christmas tree quality.
- Assessing the Cost and Operational Feasibility of "Green" Hardwood Winter Inventory for Southeastern Pulp MillsGallagher, Thomas V. (Virginia Tech, 2003-05-23)Procuring hardwood pulpwood during the winter months for a pulp mill in the Southeast can be difficult. Saturated soils and low soil strength make logging difficult or impossible on many sites, forcing companies to store large volumes of hardwood pulpwood in woodyards for retrieval during wet weather. Hardwood fiber readily available in large volumes on ground that is operable during wet periods at a location near the pulp mill could provide a valuable alternative wood source. Thus, the objectives of this study are to 1) develop a decision model for a manager to use to determine the feasibility of strategically located, intensively-managed, short-rotation hardwood fiber farms as pulp mill furnish, 2) use the model to estimate wood costs for a hypothetical eastern cottonwood plantation, and 3) use the model to determine if a fiber farm grown on drier, upland sites ("green" inventory) could be used to reduce woodyard winter inventories and economically supply a nearby pulp mill during a wood shortage, thus reducing high cost, emergency "spot market" wood purchases. The decision model is incorporated in a spreadsheet and includes all the costs typical for a fiber farm. The model is tested using current establishment and management costs from the literature and yields from an experimental fiber farm in the southeast. Under current yields, delivered costs from the fiber farm averages $71/ton. With potential increased yields that could occur with genetic improvements and operational optimizations, delivered cost for fiber farm wood could be reduced to $56/ton. In comparison, the highest cost wood purchased by the three cooperating pulp mills during the study period was $50.23/ton. The net present values of a fiber farm as "green" inventory were determined using actual wood cost and inventory levels from three cooperating southeastern pulp mills. For the "green" inventory analysis, all three pulp mills would have lowered their overall wood cost using a fiber farm (with higher yield) as "green" inventory, primarily by reducing the amount of wood required as dry inventory on woodyards. Savings accrued during "dry" years offset the higher cost of hardwood plantation deliveries. A sensitivity analysis was performed to determine the optimal size fiber farm for one of the cooperating pulp mills and indicated that 800 acres would be the most beneficial.
- Assessment of silvicultural practices to improve survival and growth of pioneer and mid-successional hardwoods on old field restoration sitesSteele, Jason Keith (Virginia Tech, 2020-07-01)Survival and growth of planted trees are common indices used to evaluate success of wetland restoration efforts used to compensate for wetland losses. Restoration efforts on marginal agricultural lands typically result in less than satisfactory survival and growth of desired tree species. This study evaluated seed source ecotype, greenhouse preconditioning and combinations of five mechanical site preparation techniques (mound, bed, rip, disk, pit), four levels of planting stock (gallon, tubeling, bare root, and direct seed), and three planting aids (mat, tube, none) on the survival and growth of American sycamore (Platanus occidentalis L.) and willow oak (Quercus phellos L.) planted on an old field riparian area in the Virginia Piedmont. American sycamore seedlings subjected to greenhouse flood preconditioning had 25% greater height and willow oak seedlings grown under normal greenhouse conditions had 18% greater diameter, but these greenhouse adaptations did not confer greater survivability or growth after field planting. American sycamore seeds sourced from dry ecotypes were 14% taller than wet ecotype seeds, and willow oak acorns sourced from wet ecotypes were 11% taller than dry ecotype acorns, indicating that parental ecotype may influence survivability and growth. The combination of mounding site preparation and gallon planting stock increased mean survival to 100% and aboveground dry biomass (5.44 Mg/ha/yr) in American sycamore. Willow oak had 45% greater woody stem volume with mounding site preparation 80% greater woody stem volume with gallon and bare root planting stock. Tubeling planting stock provided significant benefit relative to the low planting stock cost for American sycamore, while bare root seedlings were shown to be an effective planting stock for willow oak. The use of appropriate ecotype seed sources, use of mounding mechanical site preparation techniques and planting of species appropriate planting stock increased survival and growth of common early and mid-successional Piedmont tree species on marginal agricultural lands. Treatments that appear to be economically viable for restoration and mitigation efforts could potentially offer other economic incentives such as short rotation woody crops and timber value, which might induce additional private landowners to attempt restoration efforts in marginal old field riparian areas.
- Burkholderia phytofirmans strain PsJN effects on drought resistance, physiological responses and growth of switchgrassWang, Bingxue (Virginia Tech, 2015-02-09)To decrease dependency of fossil fuels and avoid direct competition with food crops, massive research efforts are investigating next-generation cellulose biofuel crops such as switchgrass (Panicum virgatum). A low-input, sustainable switchgrass production could be achieved by reducing traditional management practices though applying plant growth promoting rhizobacteria (PGPR), of which our understanding is still rather limited. To elucidate physiological mechanisms behind PGPR's beneficial effects, we inoculated switchgrass seedlings with Burkholderia phytofirmans strain PsJN. Two experiments were conducted to determine the initial and long-term responses of switchgrass to PsJN inoculation by tracking growth and leaf physiology. In a third experiments, we tested the effects of PsJN on growth and leaf-level physiology of switchgrass under a moderate pre-drought conditioning and a successive severe drought stress. PsJN inoculation increased biomass and promoted elongation of shoots within 17 days following inoculation. The enhanced root growth in PsJN inoculated plants lagged behind the shoot response, resulting in greater allocation to aboveground growth (p=0.0041). Lower specific root length (p=0.0158) and higher specific leaf weight (p=0.0029) were also observed in PsJN inoculated seedlings, indicating advanced development. Photosynthetic rates (Ps) were higher in PsJN inoculated seedlings after 17 days (54%, p=0.0016), which were related to higher stomatal conductance, greater water use efficiency, and lower non-stomatal limitation of Ps. These rapid changes in leaf physiology are at least partially responsible for switchgrass growth enhancement from PsJN treatment. The early growth enhancement in PsJN inoculated switchgrass linearly decreased with plant age. PsJN inoculation increased Ps of upper canopy leaves by 13.6% but reduced Ps of lower canopy leaves by 8.2%. Accelerated leaf senescence and early flowering were observed in PsJN-inoculated switchgrass, which might contribute to slightly lower aboveground biomass at final harvesting. Drought preconditioning increased Ps of PsJN-inoculated switchgrass during a later severe drought; whereas, control switchgrass only benefited from drought preconditioning when leaf water potential dropped below -1 MPa. This study verified early growth enhancement and accelerated development of switchgrass due to PsJN inoculation. Rapid improvement in leaf physiology is related to enhanced productivity. PsJN inoculation also improve drought tolerance of switchgrass.
- Challenges in the Greenhouse Production of Rosmarinus officinalis L.Westervelt, Paul Matthew (Virginia Tech, 2003-07-28)Rosmarinus officinalis L. (rosemary) is popular as a culinary herb, landscape plant, and potted florist's crop. Little research has been reported on the greenhouse production of this plant. Effects of irrigation rate, fertilizer concentration, and growing media on root and shoot growth were investigated for R. officinalis 'Athens Blue Spires'. In the first experiment, rooted cuttings were potted and received fertilizer treatments of 100, 200, or 300 mg?L-1 nitrogen (N) from 15N-2.2P-12.2K water-soluble fertilizer for twelve weeks. Two irrigation regimes were imposed - plants were irrigated with fertilizer solution when the growing media dried down to less than 30% or 20% volumetric soil moisture content. Root and shoot dry weights showed irrigation rate did not effect roots, but the higher irrigation rate produced larger shoots at all fertilizer concentrations. The largest roots and shoots were a product of the lowest fertilizer concentration. In the second experiment, rooted cuttings of the same cultivar were potted and received fertilizer treatments of 50, 100, 150, or 200 mg?L-1 N from 15N-2.2P-12.2K water-soluble fertilizer for 2, 4, 6, or 8 weeks. Plants were harvested at the end of each treatment. A third irrigation regime was imposed - plants were irrigated with fertilizer solution when the growing media dried down to less than 40%, 30%, or 20% volumetric soil moisture content. Root and shoot dry weights showed neither irrigation nor fertilizer were significant at week two, six, or eight. Dry weights showed irrigation was significant for roots at week four with the lowest irrigation rate producing the largest roots at all fertilizer concentrations except 100 mg?L-1 at the less than 30% irrigation rate. Irrigation was also significant at week four for shoots with the lowest irrigation rate producing the largest shoots at all fertilizer concentrations except 100 mg?L-1 at the less than 30% irrigation rate. In the third experiment 'Athens Blue Spires' rooted cuttings were potted in five different soilless media [Fafard 52 (24% peat, 60% bark, 8% perlite, 8% vermiculite); Fafard 3B (45% peat, 25% bark, 15% perlite, 15% vermiculite); Scott's Sierra Perennial Mix (25% peat, 65% bark, 10% perlite); Scott's Metro Mix 700 with Coir (25% coir, 50% bark, 10% perlite, 15% vermiculite); and a nursery mix (89% pine bark, 11% sand)]. Plants were irrigated for fourteen weeks with 150 mg?L-1N fertilizer solution when the growing media dried down to less than 30% or <20% volumetric soil moisture content. Growing media affected shoot dry weight with the highest-percentage peat media (Fafard 3B) producing the largest plants. All were of marketable quality. Irrigation rate did not affect root dry weight, but the higher rate produced larger shoots in each of the five media. The fourth experiment examined the growth of R. officinalis 'Tuscan Blue' rooted cuttings when planted in five different growing media [Fafard 52, Fafard 3B, Scott's Perennial, Metro Mix 560 with coir (30% coir, 15% peat, 40% bark, and 15% perlite), and 100% pine bark]. A third irrigation regime was imposed - plants were irrigated with 150 mg?L-1N fertilizer solution when the growing media dried down to less than 40%, 30%, or 20% volumetric soil moisture content. Treatments lasted for 2, 4, 6, or 8 weeks and plants were harvested at the end of each treatment. Dry weights showed neither media nor irrigation was significant for roots or shoots at weeks four or eight. However, at week two, media significantly affected root dry weight with the heaviest roots produced by the two perennial mixes (Scott's perennial and Fafard 52). Growing media affected shoot dry weight at week six with the highest-percentage peat media (Fafard 3B) producing the largest plants at the low and high irrigation rate. Irrigation also affected root dry weight at week six with the two lowest irrigation rates producing the heaviest roots in all media.
- Characterization of water stress during cold storage and establishment for Acer platanoides and Crataegus phaenopyrumBates, Ricky Martin (Virginia Tech, 1994-08-01)This study examined the affects of desiccation during and after cold storage on the physiology, growth, and marketability of bare-root Acer platanoides (Norway maple), Crataegus phaenopyrum (Washington hawthorn) and Prunus x yedoensis (Yoshino cherry). Histological examination of Acer and Crataegus stems was also conducted. Maple and cherry trees were transplanted into pine bark-filled containers and subjected to mist or non-mist treatments. Xylem water potential increased (became less negative) for misted maple and cherry trees. Water potential increased for non-misted maple and decreased for non-misted cherry trees. Maple and hawthorn seedlings were subjected to cold storage durations of 2, 4, 6, 8, 10, and 12 weeks and storage treatments: whole plant covered, shoots exposed, roots exposed and whole plant exposed. Shoot (Ψs) and root (Ψr) water potentials for all treatments and both species decreased during storage. For maple, (Ψs) and (Ψr) of the exposed shoot treatment were the same as the whole plant covered treatment. In contrast, hawthorn (Ψs) and (Ψr) of the exposed shoot treatment were lower (more negative) than for the whole plant covered treatment. Root hydraulic conductivity was the same for both species and decreased with increased storage duration and for treatments with exposed roots. For the root covered treatments, maple root growth potential (RGP) increased while hawthorn RGP decreased with increased cold storage duration. RGP for both species remained low throughout storage for treatments exposing roots. Days to bud break for Acer and Crataegus seedlings decreased with increased storage time for the whole plant covered treatments but increased for both species when stored with exposed roots. Maple marketability, percent of trees with ≤ 10% shoot dieback, for root covered treatments was high for most storage durations. Hawthorn marketability was generally low except for the whole plant covered treatment during the first six weeks of storage. There was a high positive correlation between RGP and marketability for both maple and hawthorn. Histological examination revealed that Acer stems had a highly suberized periderm, and a uniform cuticle with few disruptions. Periderm suberization of Crataegus stems was variable and extensive peridermal cracking was evident. Cuticle wax decreased with increasing distance from the stem apex for both species. Collectively, results indicated that hawthorn stems had more pathways for water loss than maple shoots. While protection of roots of all bare-root stock is important, desiccation sensitive species such as Washington hawthorn require both root and shoot protection during storage and at transplanting to minimize water loss.
- Characterizing the Respiration of Stems and Roots of Three Hardwood Tree Species in the Great Smoky MountainsRakonczay, 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.
- Chemical, Physical, and Biological Factors Influencing Nutrient Availability and Plant Growth in a Pine Tree SubstrateJackson, Brian Eugene (Virginia Tech, 2008-10-24)Pine tree substrate (PTS) produced from freshly harvested loblolly pine (Pinus taeda L.) trees has potential for replacing or reducing the use of aged pine bark (PB) and peat moss as container substrates for horticulture crop production. The objective of this work was to determine the factors influencing nutrient availability in PTS compared to PB or peat substrates. Chapter two reports data on the response of japanese holly and azalea to fertilizer rate when grown in PTS and PB. This study demonstrated that an additional 2.4 kg·m-3 of Osmocote Plus (15N-3.9P-10K) controlled release fertilizer is required for both species when grown in PTS compared to PB. Data are reported in chapter three on the effects of fertilizer rate, substrate particle size, and peat amendment on growth and floral quality, and on post-production time-to-wilting of poinsettias. Data from this work show that PTS requires an additional 100 mg·L-1 N to grow poinsettias comparable to plants grown in peat unless the particle size of PTS was decreased or 25% peat was added, in which case no additional fertilizer was needed. Results also indicated that PTS shrinkage was similar to that of peat, and that post-production time-to-wilting in PTS plants was similar as plants grown in peat. Data in chapter four compares nitrogen (N) immobilization rates, substrate carbon dioxide (CO₂) efflux levels, and nutrient leaching in peat, PB, and PTS over time. Data from these studies indicated that more N immobilization occurs in PTS than in PB or peat and that the substrate CO₂ efflux levels (estimate of microbial activity) corresponds to N immobilization in all substrates. Nutrient availability, changes in physical and chemical properties, substrate shrinkage, and microbial activity in PTS compared to PB during long-term nursery production are reported in chapter five. Results showed that substrate nutrient levels remain lower in PTS and that pH levels of PTS decrease considerably over two growing seasons compared to PB. Results also indicate that PTS does decompose over time in containers, but substrate shrinkage of PTS is similar to that of PL and PB during crop production.
- The combined effects of fertilization and relative water limitation on tissue water relations, hydraulic parameters and shallow root distribution in loblolly pine (Pinus taeda L.)Russell, Edward Morgan (Virginia Tech, 2019-08-27)One goal of this research was to characterize shoot tissue-level responses in loblolly pine to soil moisture limitation in combination with fertilization as well as to more severe soil moisture limitation. We found that neither fertilization alone, nor fertilization in combination with soil moisture limitation resulted in changes to shoot tissue water relations parameters classically characterized in drought response studies. More severe water limitation was necessary to elicit responses, and those responses had not been fully described previously. The more severe water limitation resulted in increased capacitance beyond turgor loss, increased relative water content at turgor loss, a more negative turgor loss point, an increased bulk modulus of elasticity, more negative osmotic potential at 100% relative water content, and an increased apoplastic water fraction. As there were indications of reduced water use and moisture stress in the absence of shoot level responses under less severe drought, such parameters are insufficient alone to characterize moisture stress in fertilized and in less severely water limited loblolly trees. Additionally, we sought a morphological or physiological explanation for the reduced transpiration and increased water use efficiency reported for fertilized trees in the Virginia Piedmont. Our characterizations of the responses of root distribution and hydraulics to limited soil moisture here complement existing research, which demonstrated changes to root distribution and hydraulics in response to fertilization. The responses we discovered in fertilized trees that accompanied reduced transpiration and increased water use efficiency that differed from responses to reduced soil moisture alone were primarily large decreases to shallow root presence. We found this to be readily quantified using measures of root length density. Decreases to whole-tree hydraulic conductivity were also shown to occur with fertilization and were shown not to occur in shoot tissue, suggesting limitation via rhizosphere or root xylem conductance. Our results support the supposition that fertilization narrows hydraulic safety margins and potentially predisposes loblolly trees to moisture stress, particularly prolonged, severe water limitation following fertilization. Finally, we tested the validity of throughfall exclusion for simulating reduced rainfall using a greenhouse 'split-pot' study, which applied spatially fixed heterogeneous soil moisture to young, well-watered loblolly pines. The 'split-pot' experiments demonstrated that spatially fixed soil moisture heterogeneity does not confound drought effects; needle area specific transpiration was not decreased, nor was water use efficiency increased. This supports the validity of inferences taken from drought simulation experiments with loblolly pine where throughfall exclusion troughs reduce soil moisture content in a consistent, spatially heterogeneous manner.
- The combined effects of ozone, sulfur dioxide and simulated acid rain on the growth of three forest tree speciesChappelka, 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.
- Combining remotely sensed estimates of structure and function to improve quantification of forest productivityWilliams, Paige T. (Virginia Tech, 2024-09-19)Gross primary productivity (GPP) describes the total photosynthesis (i.e., carbon fixation) for an ecosystem and is an important component of the global land carbon budget. Accurate measurements of forest carbon sequestration are crucial, as climate, soils, and management practices influence carbon uptake. Disturbances such as wildfires, diseases, insect infestations, and extreme weather events significantly impact forest health and functionality. Remote sensing is useful for monitoring global ecosystems and estimating forest vitality. High-resolution images and lidar (Light Detection and Ranging) data offer enhanced insights into forest light utilization. Combining lidar with spectral data provides a comprehensive view of forest ecosystems, integrating both structural and physiological information. This work includes three separate studies under a common objective to establish an improved understanding of forest productivity in different forest compositions using a combination of physiological function from optical imagery and morphological structure from lidar. The first study investigates the photochemical reflectance index (PRI) and how illumination affects the diurnal and vertical distributions of two managed pine stands with varying ages and row orientations, using airborne hyperspectral and lidar data. We developed a novel method to classify canopy illumination into sunlit, shaded, and mixed light areas using the hyperspectral data and a simulated panchromatic band. PRI values varied between sunlit and shaded foliage throughout the day, reflecting differences in foliage efficiency depending on light conditions and forest structure. The second study evaluates how well remotely quantified plant functional traits predict GPP across U.S. forests. Using data from NEON's airborne remote sensing and in situ flux tower measurements, the study assessed hyperspectral optical indices as physiological traits and lidar-derived products as morphological and environmental traits. By developing multiple linear regression models with separated and combined trait groups, the best prediction model combined morphological, environmental, and physiological traits with a PRESS R2 of 0.75. This underscores the importance of integrating various functional traits for accurate forest productivity predictions. The last study detects insect-induced tree mortality with separated and combined models of structure from lidar and physiology from satellite imagery. Although all models tend to overestimate tree mortality, integrating lidar data enhances predictions by 6% offering valuable structural context. A central theme of this work is that lidar-derived structural measurements were crucial in every chapter.
- Comparative study of an antioxidant defense mechanism in genotypes of eastern white pine which show differential foliar characteristicsAnderson, James V. (Virginia Tech, 1990-05-06)Approximately 10-15% of field-grown eastern white pine (Pinus strobus L.) within a nursery plantation expressed foliar characteristics similar to that induced by oxidant pollution. Sensitive genotypes (based on foliar characteristics), had a 50% reduction in needle growth, severe needle tip burn, mottling, and early needle shed during a high O₃, drought-type growing season (1988) compared to a low O₃, non-drought growing season (1989). Tolerant genotypes showed little difference in needle growth or visible injury during the two growing season. Seasonal needle ascorbate concentrations were similar during the two years however, needle glutathione (GSH) content has not. Total GSH content was two-to three-fold greater in both genotypes during the summer of 1989 compared to 1988. Cloned, tolerant trees also had 23% more total GSH when exposed to forced ambient air compared to charcoal-filtered air in open-top chambers. Cloned sensitive trees had similar GSH concentrations when exposed to different chamber treatments. One-year-old needles always had lower ratios of ascorbate/ dehydroascorbate, ascorbate/α-tocopherol and GSH/GSSG than current year needles. One-year-old needles from the tolerant tree also maintained a higher glutathione reductase (GR) activity than the sensitive tree during the late summer. Needles of eastern white pine had two isoforms of GR (GRA and GRB). GRA and GRB accounted for 17% and 83% of the GR recovered, respectively. GRA and GRB had different physical and kinetic properties. Antibody produced from GRR was reactive with both native and denatured GRB, but was cross-reactive with only native GRA. Tolerant and sensitive clones exposed to control (< 0.025 ppm) or high (4.5 ppm∙hr total dose) O₃ for O to 72 hr, showed no increase in GR activity. Only in the high-O₃-treated trees did the amount of GR protein increase. Needles from the sensitive clone contained 14, 62, and 464 ng GR mgP⁻¹ and needles from the tolerant clone contained 21, 138, and 2800 ng GR mgP⁻¹ after 0, 24 and 72 hr O₃ exposure, respectively. The results of this dissertation indicate that differential foliar characteristics in eastern white pine may be correlated with GSH turnover and its regulation by GR during periods of high oxidant stress.
- Culture and Propagation of Japanese MaplePhillips, Guy (Virginia Tech, 2003-12-12)Japanese maples have maintained a steady presence in nurseries and across the suburban landscape of America for many years now. Their fineness of texture, relatively small stature, and colorful displays are attributes that have earned them the admiration of studied horticulturalists and casual observers alike. This document attempts to compile the published accounts of several decades of observations and experiments pertaining to the general culture and propagation of Japanese maples, most specifically, information pertaining to Acer palmatum. In addition to aesthetic beauty, several factors combine to make Japanese maple a valuable horticultural species. These factors are: seedling variability, wide-ranging environmental adaptability, moderate ease of asexual propagation, limited problems with pest and pathogens in both nursery and landscape settings, and consistent commercial value and appeal. Despite the popularity and overall viability of Japanese maple cultivation, information concerning the species, particularly research information, is somewhat lacking.
- Destination of Isotopic Nitrogen Fertilizer Under Varying Herbicide Regimes in a Mid-Rotation Loblolly Pine (Pinus taeda L.) Plantation in the Piedmont of Virginia, USAVan-Spanje, Megan (Virginia Tech, 2023-05-24)Mid-rotation fertilization and vegetation control are some of the most common silvicultural treatments in loblolly pine (Pinus taeda L.) plantations in the southeastern United States. Competing vegetation is commonly thought to sequester fertilizer nitrogen (N) and reduce the potential growth response to a mid-rotation fertilization treatment. This experiment aims to identify what proportion of applied N fertilizer is retained in the crop tree pine foliage, and the degree to which understory vegetation is competing for this resource. Our mid-rotation loblolly pine plantation received an application of 15N fertilization (urea 365 kg/ha, at 46% N by weight, i.e. 168 kg/ha of N) and a portion of plots received an understory vegetation control (basal spray application of triclopyr; 13.6% active ingredient) treatment either before fertilization or not at all. One-year post-fertilization, 15N contents within pine foliage, leaf fall/leaf litter, forest floor, and soil were measured, as was competing vegetation presence. There was significant variation in applied nitrogen acquisition among the different ecosystem components measured, with 0-15 cm soils retaining a majority at 32-37% added 15N. Differences in fertilizer N acquisition in pine foliage between plots with and without understory vegetation control was marginally significant (p = 0.06) with pine foliage in plots without understory vegetation capturing greater 15N (4.3% greater). Red maple (Acer rubrum) and oak species (Quercus spp.) were the most common competitors but neither had a uniquely pronounced effect on pine nitrogen sequestration. My data indicate that increasing competition reduces fertilizer N foliar concentrations in crop pine trees but at a modest rate and equally across species groups. An unrefined threshold determining when fertilizer N capture in crop pine trees was affected was found at 3.1 m2/ha of competing vegetation basal area. This site will continue to be monitored over time to assess fertilizer N retention in loblolly pine each year after fertilization and evaluate the fertilizer N capture within competing vegetation.
- Do Roots Bind Soil? Comparing the Physical and Biological Role of Plant Roots in Streambank Fluvial ErosionSmith, Daniel Jeremy (Virginia Tech, 2022-09-22)This study is the first to consider how the combination of root physical effects, microbial production of EPS, and root effects on the hydrodynamic boundary layer could influence streambank soil erodibility. Specifically, the goal of this research was to quantify the physical and biological effects of roots on streambank fluvial erosion. A series of laboratory-scale erosion tests were conducted using a mini jet erosion testing device and a recirculating flume channel to address this goal. Several soil and vegetation factors that influence fluvial entrainment, like extracellular polymeric substances (EPS), soil aggregate stability and root length density, were measured following erosion testing. For flume experiments, three streambank boundary conditions were constructed to simulate unvegetated streambanks, as well as streambanks with herbaceous and woody roots. Soil treatments were also created to represent unamended and organic matter (OM) amended soil either without roots (bare soil), with synthetic roots, or with living roots (Panicum virgatum). Median soil erosion rates along the simulated rooted boundaries were two to ten times higher compared to the unvegetated boundary due to protruding root impacts on the boundary layer. In flume experiments, median erosion rates were 30% to 72% lower for unamended soils containing compacted synthetic root fibers as compared to bare soil samples. Adding both OM and fibers to the soil had a greater effect; the median erosion rate reductions of live rooted treatments (95% to 100%) and synthetic rooted + OM treatments (86% to 100%) were similar and statistically lower than bare soil controls. Stimulated microbial production of EPS proteins were significantly correlated with increased erosion resistance in OM-amended treatments while OM treatments had significantly lower EPS carbohydrates compared to unamended treatments. In summary, while sparsely spaced roots exposed on streambanks may increase soil erosion rates due to impacts on the hydrodynamic boundary layer, overall results highlight how the synergistic relationship between root fibers and soil microbes can significantly reduce streambank soil erodibility due to fiber reinforcement and EPS production.
- Drought resistance and gum yield performances in a Senegalia senegal (L.) Britton progeny trial in SenegalSarr, Mame Sokhna; Seiler, John R.; Sullivan, Jay; Diallo, Adja M.; Strahm, Brian D. (2021-01-18)With continued global change as a result of land use changes, invasive species and changing climatic patterns, it is becoming increasingly important to understand the adaptability of Senegalia senegal provenances to maximize resilience in managed and natural populations of this species. The objective of this study is to investigate Senegalia senegal genotypic differences in water use efficiency (WUE) measured by stable C-13 isotope composition in foliage according to their ploidy levels. Secondary objectives are to discuss inherent adaptive variation related to soil pH, survival, growth indexes, gum arabic yield and WUE within provenance in the climate change context. A Senegalia senegal progeny trial, in Dahra, Senegal was used in this study: 443 adult trees consisting of 60 families nested within 4 provenances were assessed in this study. Results showed significant differences in gum yield among provenances (P = 0.0002) and families (P < 0.0001). Diamenar and Ngane provenances showed overall similar annual gum yield despite a lower tree survival rate of Ngane than Diamenar. Growth traits, especially stem volume index and crown area index were larger on Ngane provenance, which also displayed significantly higher foliar WUE and lower leaf area index (LAI) than the other provenances. WUE was positively correlated with gum yield (P = 0.0302), but the coefficient of determination was only 2%. Foliar delta C-13 varied significantly (P < 0.0001) between diploids (- 27.91 parts per thousand) and polyploids (- 27.12 parts per thousand). However, within each provenance no significant difference was found. Only 15% of isotope compositions could be explained by ploidy level variation. Differences found in growth and gum yield may be attributed to genotype-specific variation. However, a significant correlation between soil pH and tree survival rate was found (P = 0.0051; r = 0.60). This study confirmed a possible improvement of the gum arabic sector through genotype based selection. Ngane and Diamenar seem to be more profitable to grow in Dahra than the other tested provenances. Future research should investigate the effect of soil pH, other soil physical and chemical properties, and management activities to improve site quality on tree survival and gum yields among provenances. Further, more research is needed to clarify inherent traits underlying drought tolerance in the field and gum yield performance.
- Eastern Hemlock Needle Physiology as Impacted by Hemlock Wooly Adelgid and Treatment with ImidaclopridMcDonald, Kelly Marie (Virginia Tech, 2013-11-18)Eastern hemlock (Tsuga canadensis [L.] Carr.) is a foundation species that occupies a unique niche in forest ecosystems and which often forms pure stands throughout the eastern United States. Throughout the last half of a century, widespread mortality of T. canadensis had been occurring with the introduction of the invasive pest, hemlock woolly adelgid (Adelges tsugae Annand) (HWA). HWA now threatens to destroy millions of hectares of hemlock dominated forests and to disrupt its associated ecosystems. In order to determine how HWA impacts hemlock physiology, three sites with various degrees of infestation were chosen and half of the trees at each site were treated with imidacloprid (Merit® 2 F, Bayer, Kansas City, MO) while the rest were left untreated. Needle gas exchange was assessed monthly using a LI-COR 6400 portable open path gas exchange system (LI-COR Inc, Lincoln NE). Chlorophyll fluorescence and bud break were also characterized for all trees at two of the three sites. After one complete growing season, we found a slight increase in photosynthetic rates (4.98 %), increased bud break at Fishburn (562 %) and Mountain Lake (25.6 %) sites, and no change in chlorophyll fluorescence for imidacloprid treated trees. These results suggest that HWA is causing tree mortality largely through a reduction of leaf area and not a reduction in leaf level photosynthetic capacity. By quantifying the physiological response of T. canadensis to HWA, better insights can be made into understanding tree decline as it relates to HWA.
- Ecohydrology and self-organization of black ash wetlandsDiamond, Jacob S. (Virginia Tech, 2019-04-19)Wetlands self-organize through reciprocal controls between vegetation and hydrology, but external disturbance may disrupt these feedbacks with consequent changes to ecosystem state. Imminent and widespread emerald ash borer (EAB) infestation throughout North America has raised concern over possible ecosystem state shifts in forested wetlands (i.e., to wetter, more herbaceous systems) and loss of forest function, calling for informed landscape-scale management strategies. In this dissertation, I use black ash wetlands as a model system to understand complex ecohydrological dynamics, and I use these dynamics to explain the self-organization of observed patterns in vegetation, hydrology, and microtopographic structure. The combined inferences from the three research chapters strongly implicate black ash trees as autogenic ecosystem engineers, who, through the process of improving their local growing conditions, cause a cascade of environmental changes that result in a unique ecosystem structure. This unique ecosystem structure is under existential threat from the invasive EAB. Through experiment, I show that loss of black ash trees to EAB induces persistent shifts in hydrology that result from reduced evapotranspiration and subsequent changes to water table regime (Chapter 2). These results suggest the potential for catastrophic shifts of black ash wetlands from forested to non-forested, marsh-like states under a do-nothing EAB management scenario. However, research presented here suggests that preemptive management of black ash wetlands can potentially mitigate loss of desirable forested conditions. Forest management to replace black ash with other wetland canopy species may be a slow and steady path towards forest maintenance, and harvesting may facilitate establishment of alternative species. In the case of preemptive harvesting of black ash, I posit that maintenance of microtopographic structure, either through leaving downed woody debris or through physical creation, is paramount to forest recovery. Microtopography in these ecosystems provides crucial relief from anaerobic stress generated by higher water tables, allowing woody species to persist on elevated microsites (e.g., 30 cm above base soil elevation). Moreover, I show that microtopography in black ash wetlands has clear structure and pattern and that its presence arises from self-organizing processes, driven by feedbacks among hydrology, biota, and soils (Chapter 3). I further show that this structured and non-random microtopography has profound influence on biogeochemical processes in black ash wetlands, controlling plant richness and biomass, and soil chemistry gradients (Chapter 4). Based on this work, I propose that structured wetland microtopography is a diagnostic feature of strongly coupled plant-water interactions, and these interactions may be important for ecosystem resilience to disturbance.