Master of Science (M.S.), University of Dayton, 2023, Biology

The structure and composition of forest ecosystems throughout eastern North America has been determined by historical disturbances and successional processes. The white oak group (Leucobalanus) was an important species culturally for Indigenous Peoples of eastern North America for hundreds of years and has been highly valued by European colonizers of the 18th and 19th centuries. The white oak tree (Quercus alba) is a geographically widespread species in eastern North America that has historically been a forest dominant. In addition to popular human uses, Q. alba acorns are an important resource for wildlife. Over the past century, despite being a canopy dominant, Q. alba along with other oaks have exhibited a striking lack of regeneration and recruitment into the canopy across much of its range. This regeneration failure has been associated with a dramatic increase in the importance of shade-tolerant maple species (Acer spp.). A transition from oak-to-maple dominance could have largescale effects on biodiversity, wildlife, and soil characteristics. A variety of explanations for this oak-to-maple dominance shift have been offered in the scientific literature, predominant among these is the multiple interactive drivers hypothesis that asserts historical oak dominance was created by the interaction of multiple disturbance processes. Much remains unknown about the causes of oak-to-maple dominance shift and the multiple drivers hypothesis has not been fully vetted. In this Thesis I sought to examine factors that led to formation of Q. alba dominated forests over the past century by focusing on tree-ring analysis in forests of southwestern Ohio. These forests are near the geographic center of the Q. alba range and are broadly characteristic of the ecology in oak forests of eastern North America. I examined cross section samples of Q. alba (n = 62), chestnut oak (Q. montana) (n = 2), and shagbark hickory (Carya ovata) (n = 1) trees to assess (a) long- (open full item for complete abstract)

Committee: Ryan McEwan (Advisor); Jenn Hellmann (Committee Member); Chelse Prather (Committee Member) Subjects: Biology; Ecology; Environmental Management; Environmental Science

Master of Science, The Ohio State University, 2009, Plant Pathology

Phytophthora spp., especially invasives, are endangering forests globally. P. ramorum causes lethal canker diseases on coast live oak (CLO) and tanoak, and inoculation studies have demonstrated pathogenicity on other North American oak species, particularly those in the red oak group such as northern red oak (NRO). No practical controls are available for this disease, and characterization of natural resistance is highly desirable. Variation in resistance to P. ramorum has been observed in CLO in both naturally infected trees and controlled inoculations. Previous studies suggested that phloem phenolic chemistry may play a role in induced defense responses to P. ramorum in CLO (Ockels et al. 2007) but did not establish a relationship between these defense responses and actual resistance.Here we describe investigations aiming to elucidate the role of constitutive phenolics in resistance by quantifying relationships between concentrations of individual compounds, total phenolics, and actual resistance in CLO and NRO. Four experiments were conducted. In the first, we used cohorts of CLOs previously characterized as relatively resistant (R) or susceptible (S). Constitutive (pre-inoculation) phenolics were extracted from R and S branches on three different dates. Additional branches from the same trees were inoculated in the greenhouse at the time of phloem sampling to confirm relative resistance. In the second experiment, concentrations and variation in phenolic profiles of CLOs exhibiting apparent field resistance were compared to symptomatic (i.e. susceptible) trees. In the third experiment, half-sib families of one-yr-old NRO were inoculated on two occasions and their relative resistance evaluated against concentrations of constitutive phenolics. Certain phenolics were found in higher concentrations in more resistant NROs and CLOs, and their potential use as biomarkers of resistance is discussed. In the fourth experiment, NROs were treated with methyl jasmonate, a phyt (open full item for complete abstract)

Committee: Pierluigi Bonello PhD (Advisor); Laurence Madden PhD (Committee Member); Robert Long PhD (Committee Member); Dennis Lewandowski PhD (Committee Member) Subjects: Ecology; Forestry; Plant Pathology

Doctor of Philosophy (PhD), Ohio University, 2006, Plant Biology (Arts and Sciences)

Forests are characterized by dynamism in species composition, structure and function. These dynamics, in turn, are often related to disturbance. These disturbances, therefore, are intrinsically linked to the biology of forest ecosystems. In order to understand and ultimately manage forest ecosystems, the role of disturbance in the systems must be ascertained. Disturbances that occur in forests rarely kill all of the existing trees. Therefore evidence of disturbance in the surrounding landscape is often recorded as a growth response in the surviving trees. In this dissertation I present four projects that were executed to develop an understanding of disturbance and growth dynamics in deciduous forest ecosystems of eastern North America. In each project, analysis of tree-rings (dendroecology), was used as the primary data source in the analyses. The first project focuses on the growth of American chestnut (Castanea dentata) in a Wisconsin oak forest. Castanea dentata exhibited a range of growth responses suggesting plasticity in ecological response that 1) offers promise for restoration efforts and 2) may have contributed to its dominance prior to the chestnut blight. The second dissertation project addresses anthropogenic disturbance and the formation of oak savanna in central Kentucky. Because of the > 300 year depth of the chronology in this project, I was able to develop a hypothetical model linking human population dynamics, land use eras, and ecosystem structure. The third and fourth projects work in tandem. The third project presented a vetting of the commonly employed technique of fire-history reconstruction using fire scars in oak samples. In this project we show that 1) scarring occurs from sources other than fire in the landscape, and 2) that multiple annual fires may not be recorded in the tree-ring record. Overall, the tree-ring record proved effective in fire history reconstruction. In the final project of the dissertation, I used this technique to devel (open full item for complete abstract)

Committee: Brian McCarthy (Advisor) Subjects:

Master of Science, University of Toledo, 2013, Biology (Ecology)

Extreme weather events are a growing focus of global climate change research. Extreme events, which occur abruptly and unpredictably, are often more detrimental to terrestrial vegetation than gradual shifts in climate. One type of event, the summer heat wave, may already be increasing in some areas of the world. Large-scale reductions in Net Primary Productivity and mortality have been reported during heat waves in forested ecosystems. Unfortunately, our understanding of how abrupt heat-stress affects woody species during heat waves lags behind our knowledge of herbaceous species that have been more widely studied in experimental manipulations. A few studies of herbaceous species also suggest that the coupling of soil heating to air heating can change the overall plant response to heat waves. To investigate air vs. air+soil heating in woody species, we manipulated the temperature of both shoots and roots separately for both white and black oak seedlings by insulating the soil during heat-stress to the shoot (35 vs. 40°C for 4 days, white oak; 35°C for 8 days, black oak). Interestingly, at moderate heat-stress temperature (35°C), net photosynthesis declined and internal CO2 concentration of leaves increased more when the roots were insulated in both species. Hence, concurrent soil warming prevented metabolic damage to leaves during moderate heat-stress, suggesting that direct heat to the roots increased shoot thermotolerance. In both experiments, differences in air vs. air+soil heating effects on root respiration were directly related to differences in soil temperatures, such that root respiration was higher with air+soil heating. In neither experiment were soil temperature effects related to plant water status. These results suggest that both direct and indirect effects of soil warming may occur in woody species during a heat wave, but that the response may depend on the severity and duration of the heat-stress. Future research is needed to determine t (open full item for complete abstract)

Committee: Scott Heckathorn (Committee Chair); Daryl Moorhead (Committee Member); Wayne Shepperd (Committee Member) Subjects: Ecology; Environmental Science; Forestry; Physiology; Plant Biology; Plant Sciences; Urban Forestry