Trees provide numerous benefits crucial to urban environments, yet poor growing conditions often prevent trees from reaching their genetic potential for growth, longevity, and ecosystem function. To overcome these limitations, greater understanding of tree growth in the urban environment is needed. The goal of this research project was therefore to characterize a broad suite of soil characteristics associated with urban tree plantings and evaluate their suitability for modeling physical dimensions and growth rates of urban trees. A series of observational studies and experiments was conducted on urban soils inhabited by two tree species (Zelkova serrata (Thunb.) Mikano and Quercus phellos L.) in Washington, DC and one tree species (Quercus virginiana Mill.) in Jacksonville, FL – two major metropolitan areas of the eastern United States with contrasting climate and soils. Characterization of urban soil attributes within cities revealed low variability for some properties (soil texture, pH, and certain plant nutrients with coefficients of variation (CV) below 0.5), but high variability (CV>1.0) for others (nitrate, ammonium, copper, and zinc). This is dependent on the location. These findings suggest that tree planting site evaluations may not require measurements for all soil properties and that representative sampling may be sufficient to accurately characterize most soil properties within a city. Field assessment of urban tree soils also revealed that conventional measures of soil compaction are difficult to obtain due to obstructions by roots and other foreign objects. To address the critical need for efficient and reliable assessment of soil compaction around urban trees, an experiment was conducted to develop bulk density estimation models for four common soil texture classes using soil strength and soil moisture as predictor variables. These models provided medium (0.42) to high (0.85) coefficients of determination when volumetric water content (VWC) was log transformed, demonstrating that measurements of soil texture, strength, and moisture can provide rapid, reliable assessment of soil compaction. Tree growth modeling focused on three response variables: canopy projection (CP), canopy volume (CV), and peak-increment-area age (PIA). To calculate PIA, tree-ring analysis was used to determine the age at which maximal trunk diameter growth occurred between transplanting and time of sampling. Because Q. virginiana has difficult-to-distinguish growth rings, an intensive tree-ring analysis of cores collected from these trees was conducted. The analysis revealed interseries correlation coefficients of up to 0.66, demonstrating that Q. virginiana can be aged with fairly high confidence in an urban setting. Empirical models developed for all three tree species using the suite of soil and site variables explained 25% – 83% of the observed variability in tree physical dimensions and growth rates. Soil pH was found to be a significant predictor variable for the majority of growth models along with nutrients such as Fe, B, Mn, and Zn, which are also associated with soil alkalinity. Models for PIA possessed the highest coefficient of determination, suggesting that measurements of soil conditions can be used confidently to predict the age at which growth rate subsides in these species. CV and CP were not predicted as well by soil-related variables, presumably because above-ground constraints such as pruning and building encroachment can affect canopy size without necessarily affecting growth rate. Certain prediction models for all three species included predictor variables with counterintuitive influences on tree growth (e.g., negative influences of soil depth on Q. phellos and soil volume on Q. virginiana), suggesting that either these urban trees are responding to these variables in a novel manner or that variables unaccounted for in these models (perhaps related to urbanization or high vehicular traffic) are concomitantly influencing tree growth. / Ph. D.

Beginning in the late 1930s, fire exclusion has drastically altered the vegetation dynamics of the southern Appalachian Mountains. Extremely low fire frequency has allowed for more shade-tolerant species to invade once predominantly open forests and has made it almost impossible for fire-dependent species to establish on a site. One such species is the endangered Peters Mountain mallow (Iliamna corei Sherff.) located on Peters Mountain in The Nature Conservancy s Narrows Preserve in Giles County, Virginia. This paper focuses on the fire history and stand dynamics of Peters Mountain and how fire exclusion has altered the forest composition. The historic fire frequency and successional changes discovered here may provide an insight into management strategies for the mallow. Seventy-nine fire scarred cross-sections were taken and aged to determine fire history dates and frequencies. Three 50x20 meter plots were set up on opposing aspects: northwest and southeast. The aspects were chosen at the direction of The Nature Conservancy personnel. All trees within were identified, cored and aged to determine species composition and the establishment dates of all trees. Fire history analysis revealed a mean fire interval of 2.48 years, a Weibull median fire interval of 2.18 years and a 25 percent scarred class mean fire interval of 12.5 years. Stand dynamic results show that Quercus montana has established on Peters Mountain prior to fire exclusion and remains the dominate species on the landscape. An increased number of fire intolerant species (including Acer rubrum, Sassfras albidum, Nyssa sylvatica) have been establishing on Peters Mountain during the decades of decreased fire frequency, suggesting a shift in forest composition. Frequent fires are suggested for mallow management and oak forest maintenance.

No description available.

The fractionation of two biomass resources, red oak (Quercus rubra) chips and oil palm (Elaeis guineensis) trunk solids, into constitutive chemical components, cellulose, hemicelluloses (called "other carbohydrates") and non-carbohydrates (includes lignin, tannins, etc.), was studied quantitatively in terms of relative cleanness. Red oak chips were steam exploded using a batch reactor at five different treatment severities, Ro 5,000, 10,000, 15,000, 20,000 and 35,000. Steam exploded fibers (SEF) of each severity were extracted with water and alkali. Mass fractionation and summative analysis data of all solid biomass fractions were determined. These data were interpreted in term of a unifying clean fractionation concept designed to evaluate the effectiveness of the fractionation processes. Within a series of severities applied to a single biomass resource, the quantitative clean fractionation can be used to choose an optimum severity for the isolation of any particular component fraction. The red oak results revealed that 25 % (on average) of biomass solids were lost during steam explosion. Cellulose remained almost unaffected (retained in fibers form) by water and alkali extraction. About 35-55 % of the hemicelluloses can be recovered in the water extracted liquor fraction (WEL). The remaining non-cellulosic carbohydrates were lost during steam explosion, especially at high severity. At Ro 10,000 and above, alkali extracted fibers (AEF) consists almost entirely of cellulose and non-carbohydrates. The majority of the non-carbohydrates component (> 50 %) can be isolated by alkali extraction. The non-carbohydrate component harvested increased with severity to 67% at Ro 35,000. / Master of Science

<p dir="ltr">For several decades, the ecological dominance of white oak (<i>Quercus alba</i>) has been declining throughout the species’ native range in eastern North America with failure to recruit new individuals into the overstory. White oak’s decline is concerning as the species is of great cultural, ecological, and economic value. Planting artificial regeneration is one approach to bolstering flagging natural white oak regeneration insufficient in vigor or quantity to supplant mature canopy white oak. Shelterwood harvests and artificial regeneration alone or in combination are frequently suggested to be an effective means of securing sufficient white oak regeneration in central hardwood understories. Because there is a much more comprehensive body of work examining northern red oak (<i>Quercus rubra</i>) than white oak artificial regeneration, managerial prescriptions for artificial regeneration of white oak are commonly generalized from northern red oak prescriptions. If the two species are silvically different, however, they should be managed differently to achieve maximum effectiveness of regenerative prescriptions.</p><p><br></p><p dir="ltr">I conducted both a silvicultural field trial and a more controlled shade and competition study to examine artificial white oak regeneration responses to light and competition gradients. In the silvicultural field trial, I tested the impacts of varied lengths of competition control, geographical seed source, and canopy cover on growth and survival of artificial white oak regeneration within an expanding shelterwood system. After three growing seasons, my results indicated that seedlings grow and survive at the greatest rates in areas of up to approximately 50% canopy closure, or conditions found in harvest gaps.</p><p dir="ltr">In a shade and competition study, I compared artificial northern red oak and white oak growth, morphology, and physiology responses to three light levels (10% or low, 30% or medium, and full sun or high) under the presence or absence of an invasive competitor (Amur honeysuckle (<i>Lonicera maackii</i>)). After two years, my results indicated that medium light levels resulted in the greatest height and diameter growth as well as the greatest nonstructural carbohydrate amounts in both root and shoot organs of both species. Interestingly, my physiology results indicated that northern red oak seedlings displayed lower light compensation points and greater quantum yields than white oak seedlings. These traits potentially indicate greater shade tolerance of northern red oak than white oak. Further, white oak foliar nitrogen in shaded treatments, quantum yield, and light compensation points were impacted more severely by competition than equivalent northern red oak measures, indicating that white oak seedlings may not be as well equipped to handle invasive competition pressures. These results indicate that these two upland oak species are fundamentally different, and these differences should be considered when writing management prescriptions.</p>

Tüpfel ermöglichen den interzellularen Stoffaustausch im Holzkörper. Im Zuge der Prozessgestaltung in den Bereichen Holzschutz und Zellstoffherstellung sind genauere Kenntnisse über ihren Aufbau von grundlegender Bedeutung. Das anatomische Wissen ermöglicht eine verbesserte Einschätzung der Tränkbarkeit sowie allgemein über die Eindringwege von Flüssigkeiten im Holz. Die Arbeit fasst den aktuellen Wissensstand des Baus der Tüpfel im Laubholz zusammen. Dabei stehen die in Deutschland wichtigsten Laubbaumarten, namentlich die Rot-Buche (Fagus silvatica L.) und Stiel- sowie Traubeneiche (Quercus robur L. und Quercus petraea Liebl.), im Fokus der Untersuchung. Zunächst wird der allgemeine Aufbau der Tüpfel beschrieben und besonders neuere Erkenntnisse mit aufgegriffen. Im Anschluss wird der Wissensstand zur Tüpfelbau der Rot-Buche sowie der Stiel- wie Trauben-Eiche zusammengefasst dargestellt.