Diplodia pinea causes Diplodia tip blight on more than 30 different pine species. During the past 10 years, Diplodia tip blight has emerged as a serious problem in landscape and Christmas tree farms in this region. Surveys of diseased and symptomless Austrian pines revealed that latent infections of symptomless shoots by D. pinea were common. Latent infections may account for the recently observed rapid decline of mildly diseased pines in our region. To investigate the colonization habits of D. pinea within its host, molecular cytology was attempted and traditional histology was performed on naturally infected, diseased and asymptomatic Austrian pine tissues. I devoted much effort to developing a transformation system for D. pinea. Ultimately I did not succeed in this goal, but I was able to develop a highly efficient protocol for Agrobacterium tumefaciens-mediated transformation of another pathogenic fungus, Colletotrichum graminicola, in the process. The work that I did should help in future efforts to transform D. pinea, something that will be essential if it is to become a tractable system for the study of fungal latency. Traditional histological methods were more successful, and provided important information about the nature of latent infections. Very sparse epiphytic and subcuticular fungal growth was observed in healthy shoots, however, no fungal tissues were present within the shoots. In diseased and latently infected shoots, crevices created between the needle bundles and the shoots were filled with fungal material, and hyphae were observed colonizing the needle sheaths. Hyphae were also observed breaching the shoot epidermal layer in these crevices and colonizing the underlying periderm. D. pinea colonization was extensive in all tissues of diseased shoots early in symptom development. In contrast, localized pockets of degradation were observed in the periderm and adjacent cortical cells located around areas of needle attachment in asymptomatic, latently infected shoots. The mechanism that operates to prevent expansion of these infected pockets in the latently infected shoots is still unclear. Obvious signs of pine defense mechanisms were only observed in 2 shoots. My observations were consistent with the idea that colonization progresses into the vascular tissues, and that this results in symptom development. Vascular colonization may occur more readily if the host is stressed. My research lays the groundwork for future efforts to understand the nature of the transformation from latent to pathogenic infection.

South Florida slash pine (Pinus elliottii var. densa) is the southernmost pine species in the United States and the foundation species of the globally endangered pine rockland communities in south Florida. To test if slash pine produces annual growth rings in the Lower Florida Keys, we counted the number of rings on samples collected from the North Big Pine Key site (NBP), which contained a fire scar from a known wildfire and a known date for hurricane-induced tree mortality (2006 or 2007). In addition, a crossdated tree-ring chronology (1871–2009) was developed from living trees and remnant wood found at the site and compared to divisional climate data to determine how the regional climate regime influences radial growth. Our analyses demonstrated that slash pine forms anatomically distinct, annual growth rings with the consistent year-to-year variability necessary for rigorous dendrochronological studies. Response-function and correlation analysis showed that annual growth of slash pine at NBP is primarily influenced by water availability during the growing season. However, no significant correlations were found between tree growth and the Atlantic Multidecadal Oscillation or the El Niño-Southern Oscillation. Our study reveals the potential of producing high-quality dendrochronological data in southern Florida from slash pine, which should prove useful in further studies on fire history and tree phenology and for assessing the projected impacts of impending climate change on the fragile pine rockland community.

Under normative conditions the mountain pine beetle (Dendroctonus ponderosae Hopkins) has played a regulating role in healthy lodgepole pine (Pinus contorta) forests. However, recently eruptive outbreaks that result from large pine beetle populations have destroyed vast tracts of valuable forest. The outbreaks in North America have received a great deal of attention from both the timber industry and government agencies as well as biologists and ecologists. In this dissertation we develop a landscape-scaled integrodifference equation model describing the mountain pine beetle and its effect on a lodgepole pine forest. The model is built upon a stage-structured model of a healthy lodgepole pine forest with the addition of beetle pressure in the form of an infected tree class. These infected trees are produced by successful beetle attack, modelled by response functions. Different response functions reflect different probabilities for various densities. This feature of the model allows us to test hypotheses regarding density-dependent beetle attacks. To capture the spatial aspect of beetle dispersal from infected trees we employ dispersal kernels. These provide a probabilistic model for finding given beetle densities at some distance from infected trees. Just as varied response functions model different attack dynamics, the choice of kernel can model different dispersal behavior. The modular nature of the Red Top Model yields multiple model candidates. These models allow discrimination between broad possibilities at the land scape scale: whether or not beetles are subject to a threshold effect at the lands cape scale and whether or not host selection is random or directed. We fit the model using estimating functions to two distinct types of data: aerial damage survey data and remote sensing imagery. Having constructed multiple models, we introduce a novel model selection methodology for spatial models based on facial recognition technology. Because the regions and years of aerial damage survey and remote sensing data in the Sawtooth National Recreation Area overlap, we can compare the results from data sets to address the question of whether remote sensing data actually provides insight to the system that coarser scale but less expensive and more readily available aerial damage survey data does not.

Ninety-four unmanaged lodgepole pine stands were examined to evaluate the relationship between stand density and susceptibility to mountain pine beetle attack. Sample included stands from a broad geographical range in the western United States. Beetle population trends were not significantly related to variation in stand density as measured by stand density index (SDI). The percentage of trees killed per acre by the mountain pine beetle in stands with greater than eighty percent lodgepole pine did vary significantly with changes in SDI. From these data three SDI zones were identified: 1) stands with SDI's of less than 125 showed low potential for attack, 2) stands between 125 and 250 SDI showed much greater levels of tree mortality, gradually decreasing toward the 250 SDI, 3) tree mortality decreased in stands as density increased beyond the 250 SDI value.

Mountain pine beetle (Dendroctonus ponderosae Hopkins) has caused extensive tree mortality in whitebark pine (Pinus albicaulis Engelm) forests. Previous studies conducted in various conifer forests have shown that fine surface fuels are significantly altered during a bark beetle outbreak. Bark beetle activity in conifer stands has also been shown to alter foliar fuel moisture content and chemistry over the course of the bark beetle rotation.The objective of this study was to evaluate changes to fine surface fuels, foliar fuel moisture and chemistry and litter chemistry in and under whitebark pine trees infested by mountain pine beetle. Fuels were measured beneath green (healthy) trees compared to red (two years since initial MPB attack with 50% or greater needles remaining) and gray (greater than two years since attack with between 15% and 45% needles remaining) trees. Foliar moisture content was measured in four mountain pine beetle crown condition classes: green-uninfested, green-infested (current year’s attack), yellow (last year’s attack), and red. Total terpene content was analyzed in whitebark pine needle litter and volatile terpenes were collected and analyzed from green, green-infested, yellow, and red trees.Significant differences were found in litter depths under green, red, and graytrees. Duff depths were significantly less beneath green trees than red and gray trees. One hour and ten hour fuels were more influenced by diameter and crown size than beetle crown condition classes. Foliar fuel moisture content dramatically decreased from green-infested to the red beetle crown condition class. No differences were detected in shrub and forb biomass between green, red, and gray trees. Green-infested trees had significantly lower foliar fuel moisture than green trees and by late in the season showed fuel moisture levels similar to red trees which had the lowest fuel moisture content. Litter beneath red trees contained large amounts of terpenes, including compounds known to increase foliage flammability that remain in the litter throughout the fire season. Total terpene content emitted from red foliage is greater than green-infested or yellow foliage.

Graduation date: 1996

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 73-78). Also available on the World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 134-151).

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

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