Browsing by Author "Carter, David Robert James"

Now showing 1 - 9 of 9
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    Competitive status of red spruce (Picea rubens) and Fraser fir (Abies fraseri) at ecotonal transitions in southern Appalachian sky islands
    Wetzel, Rose (Virginia Tech, 2024-07-05)
    Southern Appalachian spruce-fir sky islands are globally threatened, boreal relict forests where red spruce (Picea rubens) and Fraser fir (Abies fraseri) are dominant. Fraser fir dominates at the highest elevations with spruce-fir and spruce-dominated stands at middle elevations and hardwoods associating at lower elevations. A primary concern is encroachment of hardwoods upslope as climate change-driven milder temperatures and high precipitation confine spruce-fir forests to even higher elevations. We performed a dendrochronological analysis of growth rates in red spruce, Fraser fir, and competing hardwoods between cover types and slope aspects at six sky islands. We created linear models to test effects of aspect, cover type, and year on basal area growth measurements of red spruce, Fraser fir, and hardwoods to assess effects of competition. Growth rates were significantly affected by species, aspect, cover type, and year, and generally increased over time. Red spruce growth rates varied by combination of aspect and cover type but were greater than those of hardwoods on northern and southern aspects. Fraser fir growth rates were negative on southern-facing fir-dominated stands but increased in all other stands with the highest growth rates found in fir-dominated stands. The differences we report by cover type and aspect could help conservation practitioners prioritize treatment locations to improve climate resiliency.
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    Destination of Isotopic Nitrogen Fertilizer Under Varying Herbicide Regimes in a Mid-Rotation Loblolly Pine (Pinus taeda L.) Plantation in the Piedmont of Virginia, USA
    Van-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.
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    The Effects of Mechanical Site Preparation Treatment and Species Selection on Survival and Carbon Pools in 12-Year-Old American Sycamore (Platanus occidentalis) and Willow Oak (Quercus phellos) Riparian Plantations in the Southeastern U.S. Piedmont
    Lynn, Drake Havelock (Virginia Tech, 2024-07-16)
    Riparian wetlands may provide numerous ecosystem services, including water quality protection, food and fiber supply, wildlife habitat, and carbon sequestration. In recent years, riparian forests have received increased attention and funding for riparian forest restoration projects. Unfortunately, failures of riparian restoration efforts are likely due to mortality of planted trees. Tree mortality is commonly attributable to several factors, including selection of species that are not well suited to the wetland sites, inadequate planting densities, soil compaction associated with former agricultural activities, lack of microtopographic relief that allow small seedling to survive on wet sites, competition by herbaceous plants, and browse. Selection of well-suited species, dense planting and use of mechanical soil site preparations are all potential remedies to partially address success of wetland restoration plantings. Riparian restoration projects have historically been undertaken with goals of improving water quality and/or wildlife habitat, but in recent years there has been increased valuation of carbon sequestration. Carbon valuation appears to be increasing, but more research is needed to determine rates and pools of carbon accumulation in riparian areas. Our research quantifies forest establishment effects on multiple carbon pools in a densely planted, 12-year-old old-field riparian restoration. Our research evaluated the effects of four soil mechanical site preparations (bed, disk, pit, and mound and rip) and species selection (American sycamore (Platanus occidentalis) and willow oak, (Quercus phellos) on forest establishment and carbon storage across multiple pools, namely in planted trees, herbaceous vegetation, fine roots, organic soil horizons, and the mineral soil. At 12 years, we found that species selection was more important to carbon storage than site preparation. American sycamore was well suited to the site and had better survival than willow oak (64% vs 42% survival). American sycamore also stored more carbon across all site preparations than willow oak. Measured carbon storage averaged 74.8 Mg ha-1 for American sycamore treatments and 63.1 Mg ha-1 for willow oak treatments. The plots were densely planted (1.2 m (4ft) by 1.8 m (6ft) spacing), and forests were established even in higher mortality willow oak plots. These results indicate that high planting density is potentially a viable practice for establishing riparian forest cover, especially if desired species are marginally site suited or other survival inhibiting factors exist.
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    Estimating site susceptibility to Scotch broom dominance in young Douglas-fir plantations for control prioritization in western Washington, USA
    Boyle, Grady John (Virginia Tech, 2023-10-11)
    Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), a keystone species in western Washington, faces threats on plantations across this region from the invasive species Scotch broom (Cytisus scoparius (L.) Link), whose invasions on recently established stands can lead to mortality of Douglas-fir through overtopping. The susceptibility of sites to Scotch broom achieving dominance over Douglas-fir has been demonstrated as highly site dependent, however the site conditions that cause this have not yet been identified. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This thesis strives to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what factors improved growth of Douglas-fir during the period when they are at the greatest risk, and second, identifying factors that led to Douglas-fir outcompeting Scotch broom on sites they cohabitated. In Chapter 1, we utilized LiDAR scans, Soil Survey Geographic Database characteristics, and management histories to identify conditions that improved growth for Douglas-fir in ages 3-8. Individual tree detection was used to measure Douglas-fir heights, and a correction algorithm for LiDAR measured young Douglas-fir heights was established from field validation data. We identified that young Douglas-fir had improved growth on sites with lower elevation, flatter slopes, and finer textured soils. The factors identified were then transformed into four potential site index models based on mean stand elevation class, Mean stand elevation class and clay class, textural class and slope class, and textural class and Mean stand elevation class. In Chapter 2, we used paired field plots to examine Douglas-fir and Scotch broom competition on 19 sites across western Washington. Each site had 2 plots with only Douglas-fir and 2 plots with Douglas-fir and Scotch broom. Elevation, soil texture, and soil nutrient composition for carbon, nitrogen and available phosphorous were examined for influence on height and growth rate of both species. We identified that Scotch broom presence was negatively related to Douglas-fir height growth and that sites with either higher percentages of silt, lower concentrations of phosphorous, or higher percentages of Carbon were more likely to have growth patterns close to or exceeding Scotch broom.
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    Exploring the Impact of Climate and Productivity on Soil Carbon Across the Native Range of Loblolly Pine
    Price, Aaron Cooper (Virginia Tech, 2024-08-30)
    Policies intended to pursue climate mitigation through soil carbon sequestration require accurate estimates of soil carbon stocks and projections of how carbon pools will change with future climate. In this study, the process model MIMICS-CN was utilized to explore the potential changes in bulk soil organic carbon (SOC) and protected mineral-associated organic matter (MAOM) with changes in mean annual temperature (MAT) and annual net primary productivity (NPP) for the native range of loblolly pine (Pinus taeda L). A Monte Carlo method was used to calibrate a large ensemble of model parameters using observational data from loblolly pine stands. Spatial projections of carbon pools across the native range of loblolly pine were produced for nine temperature and productivity scenarios representing a range of likely futures. The standard deviation of the mean total SOC pool to a depth of 30 cm was 3.6 kg C m-2 while the standard deviation of potential changes in pool magnitude was 0.96 kg C m-2. Associated with regional climate change projections, increases in MAT caused losses in bulk SOC but did not affect MAOM. Simulated increases in NPP resulted in increased bulk SOC, MAOM and the proportion of SOC that is MAOM (MAOM:SOC) highlighting the importance of productivity in sequestering atmospheric CO2 in general and in protected C pools, specifically. SOC pools did not change consistently across the landscape. Rather, they varied by subregion due to differences in soil texture and changes in forecasted NPP. Soils with clay contents above 18% had the greatest potential to accumulate MAOM and bulk SOC under a realistic future climate scenarios. In regions with low clay content, significant increases in total SOC are driven by the accumulation of C in unprotected SOC sub-pools. With the maximum likely increase in NPP (31.4%), a regionwide increase in total SOC of 29% was projected whereas subregions in which NPP decreases showed no potential to increase soil carbon stocks. We conclude that the management of loblolly pine to increase productivity can increase the amount of SOC and the residence time of bulk SOC over decadal time scales, however regional differences in the proportion of C in MAOM and unprotected pools must be considered when planning silvicultural management.
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    Forest Composition, Regeneration, and Tree Quality in the Southern Appalachian Mountains of Virginia: Selective Cutting vs. Shelterwood
    Ryan, Suzanne Michelle (Virginia Tech, 2023-05-24)
    This study compared the effects of selective cutting (SC) and the first shelterwood (SW) cut in oak (Quercus)-dominated forests of western Virginia. The specific attributes compared were: (1) tree species composition; (2) seedling, sapling, and overstory tree density; (3) overstory tree quality and size; (4) sapling crown class; and (5) canopy closure. Seedlings, saplings, and overstory trees were sampled at 22 SC and 28 SW sites. Significant differences identified between the two harvest types included: biodiversity of overstory and seedling layers; species densities for seedlings, saplings, and overstory trees; species composition across forest layers; and average canopy closure. Regeneration was poorer on SC than on SW, especially among oak species where SC oak seedling density averaged 5,651 stems ha-1 and SW oak seedling density averaged 9,843 stems ha-1. Selective cutting and SW may both contribute to mesophication of oak-dominated forests in the southern Appalachian Mountains; however, SC resulted in a higher percentage of mesic species post-harvest, and the SW tended to have more oak regeneration.
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    Modeling Stem Taper of Southern Appalachian Red Spruce
    Morrone, Steven (Virginia Tech, 2023-05-24)
    Red spruce (Picea rubens Sarg.) is a commercially and ecologically important conifer species that primarily exists at northern latitudes of eastern North America. During the last glaciation, its range extended down the Appalachian Mountain chain into North Carolina and Tennessee. Since the planet warmed over the subsequent millennia, only small, sky-island populations remain at the highest peaks of the southern Appalachians where their habitat continues to be threatened by a warming climate. While they have been recognized for the rare wildlife habitat they provide in the region, these populations remain understudied. This thesis aimed to provide additional quantitative methods for managing red spruce stands through regionally fitted stem taper equations and to examine differences in stem form between the northern and southern populations of red spruce. In Chapter 1, five stem taper equations were evaluated for their ability to predict upper stem diameters and total volume in southern Appalachian red spruce: a simple linear, a quadratic polynomial, a segmented, a variable exponent, and a geometric model. Based on past studies and our results, we found that the best equations to use were the variable exponent and segmented polynomial models. Users should consider their own objectives and practical limitations in choosing which equation to use. In Chapter 2, we examined differences in stem form using three methods: a sectional rate of change in diameter, a sectional form class ratio, and a region variable added to two taper equations. The results were mixed, with the rates of change showing significant differences (p<0.05), but the form class ratios showing a mix of significant and insignificant differences. The two equations also had contrasting significance results. This made it unclear whether there were significant differences in stem form between the two populations but supported the idea that localized taper equations would provide the best results.
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    Precision Forestry: Using LiDAR to Optimize Row Thinning in Pinus taeda (L.) Plantations
    Platt, Erik James (Virginia Tech, 2024-01-24)
    Precision forestry uses information collecting techniques to detect within stand variability and inform sub-stand management treatments, such as stand thinning guidelines. This study uses LiDAR to assess individual-tree stem volumes in Pinus taeda L. plantations in the southeast US. Currently, starting rows in commercial row thinning operations are arbitrarily selected, but the study used LiDAR collected stem volume data to inform starting row selection. Three study sites were measured to provide evidence of between-row volume variability. The primary study site was set up in an alternative treatment design. Two treatments were tested: a fourth row removal scenario which removed the most volume of the four possible scenarios versus a fourth row removal which targeted the least amount of volume removed. Between-row volume variability was shown in all study sites and LiDAR data accurately assessed volume in the primary study site. The primary site saw the two blocks homogenized by their thinning treatments, demonstrating the ability to increase or decrease residual volumes using targeted row selection . Targeted row removal retained more volume and larger trees and may lead to higher harvest yields and shorter rotations. Timber managers across the globe are increasingly using remote sensing to inventory stands, thus LiDAR-informed volume acquisition may be an additional application to increase the efficiency and productivity of forests.
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    Prescribed Fire Effects on Tree Grades and Wounds on the Monongahela National Forest, WV
    Sharpe, Caroline Marie (Virginia Tech, 2022-07-01)
    Species traits, including but not exclusive to bark thickness and texture, sprouting ability, and litter bulk density and chemistry, may be related to a stem's potential to withstand potential heating from wildland fire. Trees exhibiting similarities for these properties and others may be classified into two broad functional groups: pyrophytes and pyrophobes. To our knowledge, few research studies have been conducted to determine how prescribed fires may affect wood quality of merchantable tree species in the Appalachian Mountains. Understanding potential relationships between wounding and fire tolerance may assist prescribed fire managers as they seek to promote and expand the use of prescribed fire for management purposes. To investigate this issue, six locations on the Monongahela National Forest, West Virginia, that had been subjected to one or two mixed intensity and severity prescribed fires since 2012 were selected for stand inventory in 2021. Overstory trees within these burned locations and adjacent, unburned locations were measured and graded using variable radius sampling, and additional landscape features and physiographic factors, such as aspect, elevation, and slope percentage, were also recorded at each variable radius sampling location. The most common, commercially valuable deciduous species encountered were red maple (Acer rubrum) (17.5%), white oak (Quercus alba) (9.8%), chestnut oak (Quercus montana) (32.8%), and northern red oak (Quercus rubra) (39.9%). Using field measurements and tree grades, the total number and types of wounds, potential volume loss, charring, basal area, and diameters at breast height (DBH) were compared by species, burn status (burn or control), and the number of burns. Overall, A. rubrum and Q. rubra comprised 93% of the total trees exhibiting volume loss from wounds in the burned locations. However, total volume loss only constituted about 3% of the bottommost 4.9 m log. Trees in the burned locations experiencing volume loss differed significantly between species (p=0.0294) with Q. rubra constituting 60% of volume loss trees. In burned and control plots, A. rubrum was the most commonly wounded tree with 43.5% of trees having at least one wound. Cat face and oval wounds were the only wound types resulting in volume loss. Felling and milling stems identified in this study as having potential volume loss from any fire-influenced wounds would be valuable. Furthermore, assessing the potential impact of outer bark char resulting from prescribed fires would be desired to better understand if charring constitutes any potential internal damage to stems. Deploying a similar, field-scale experiment on areas with varying fire frequencies and intensities would be useful to determine how wood quality may be affected after several prescribed burns.