An ongoing goal in forest ecology is to understand how animal populations and invasive plants affect forest communities. Reduced numbers of native tree saplings in urban forests have driven concerns that overabundant white-tailed deer (Odocoileus virginianus) populations and invasive plants are both suppressing the size and survival of native tree seedlings. Previous work has focused on the individual effects of either deer or invasive plants, but few studies have examined the combined effects of these two stressors. In this study, I examined the effects of white-tailed deer and garlic mustard (Alliaria petiolata) on transplanted seedlings of three native tree species: northern red oak (Quercus rubra), black cherry (Prunus serotina), and eastern hemlock (Tsuga canadensis). To test for their individual and combined effects on seedlings, I designed a factorial experiment where I manipulated the level of deer presence with exclosures and the level of garlic mustard presence by weeding. To measure the impacts on seedlings, I scored browse damage, tracked survival, and measured multiple size traits for each study species. I found that deer presence reduced seedling size but did not affect mortality within the short duration of the study. In addition, seedlings were not affected by garlic mustard removal, nor did the effects of deer depend on garlic mustard presence. While all species were impacted by deer, seedling browsing patterns varied among tree species. Moreover, I found that browsing by deer is changing the species composition within McMaster Forest to favour browse tolerant tree species. These results have implications for management strategies in forests with high deer densities which should prioritize controlling the deer population in addition to invasive plants and should be tailored to conserve the most sensitive species. / Thesis / Master of Science (MSc) / Reduced numbers of native tree saplings in urban forests have driven concerns that overabundant white-tailed deer populations and invasive plants are both suppressing the size and survival of native tree seedlings. In this study, I examined the effects of white-tailed deer and garlic mustard on transplanted seedlings of three native tree species: northern red oak, black cherry, and eastern hemlock. I found that deer browsing reduced seedling size but did not reduce survival. I found that browsing by deer is changing the species composition within McMaster Forest to favour browse tolerant tree species. Seedlings were not affected by garlic mustard removal, nor did the effects of deer depend on garlic mustard presence. These results have implications for management strategies in forests with high deer densities which should prioritize controlling the deer population in addition to invasive plants and should be tailored to conserve the most sensitive species.

The mechanisms that allow invasive species to flourish in novel habitats are poorly understood. A. petiolata (Alliaria petiolata) is an invader of North American forest edge and understory communities. A. petiolata’s success may result from high competitive ability due to its suppression of mycorrhizal fungi used by other species. In a greenhouse experiment, I grew 27 target species in the presence and absence of A.petiolata in soil with and without a history of A. petiolata. I found that soil with a history of A. petiolata had depleted plant available nitrogen and reduced mycorrhizal fungal colonization of target species. A. petiolata competition suppressed the growth of target species less in soils with than without A. petiolata history. Furthermore, I found that tall plants with finer roots more effectively suppressed the growth of A. petiolata. My results suggest that soil feedback effects do not improve A. petiolata’s competitive ability and are unlikely to contribute to A. petiolata invasion.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains vi, 98 p. : ill., map. Vita. Includes abstract. Includes bibliographical references.

Thesis (M.S.)--Miami University, Dept. of Botany, 2008. / Title from first page of PDF document. Includes bibliographical references (p. 22-29).

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science Degree in Biology (Ecology-track)." "A thesis entitled"--at head of title. Bibliography: leaves 28-32.

Indiana University-Purdue University Indianapolis (IUPUI) / Invasive exotic species have caused severe ecological and economic damages to many communities in the United States and elsewhere. It is therefore important to improve our understanding of how global environmental changes will affect the invasiveness and severity of these invasive species. Over the last century, anthropogenic activities have caused multiple environmental changes. Previous studies have generally focused on the impact of the increasing atmospheric CO2 level on the physiology and growth of invasive species. With atmospheric nitrogen (N) deposition on the rise over the past decades, it is essential to recognize how an increase in soil N will affect the invasiveness of some exotic species. To determine the impact of increased atmospheric N deposition and drought stress on invasive species, I studied the impact of different levels of N on Alliaria petiolata (garlic mustard), an exotic invasive species. In addition, I examined the interactive effects of N deposition and drought stress on garlic mustard. Multiple morphological measurements were used to analyze the growth rate at varying levels of N and soil moisture. The study on N deposition on plant growth will improve our understanding of the invasiveness of garlic mustard. The changes in precipitation patterns must also be examined to foresee if plants in increased atmospheric N conditions can overcome drought stress conditions. I found an increase in plant growth and photosynthetic rate at higher levels of N. Plants with adequate water displayed a continued increase from the lowest level to the highest level of N. Increases in drought stressed plants plateaued at an intermediate N level of 20 kg ha-1. My results demonstrated that during drought stress garlic mustard does not benefit from an increase in N above a certain level. These results are important to take into consideration when we analyze the spreading of invasive weeds due to global environmental changes, including increased atmospheric N deposition and regional drought, in order to apply the optimal management strategies for controlling invasive species.

No description available.

Garlic mustard (Alliaria petiolata, Brassicaceae) is a biennial herb that produces glucosinolates, a class of constituent secondary metabolites that defend against herbivores and pathogens allowing it to grow at high densities in invaded regions. The glucosinolate sinigrin is predominant in garlic mustard and aids in its competitiveness as an invasive species. In North America, garlic mustard can grow at high densities and form dense monocultures which may increase its apparency to herbivores and therefore increase its sinigrin production. I measured leaf sinigrin concentration in garlic mustard populations of different densities in the field and in greenhouse experiments to evaluate the response of sinigrin concentration and growth to density and light. Sinigrin concentrations of second-year plants were negatively correlated with growth metrics across all field densities; indicating a cost to sinigrin production. In the greenhouse density experiment with high and low rosette stem densities, sinigrin differed significantly by rosette density category. A factorial greenhouse experiment with light and density treatments discerned significant differences in sinigrin concentration by density. These findings suggest that sinigrin concentration may be influenced by intraspecific density across different light environments.

Causes and patterns of invasive plant species establishment and success depend broadly upon their ecology, including habitat suitability and interactions with other plants and animals. Here I examine the traits and distribution of invasive plants in Vermont, using spatial analysis, laboratory and field studies. I used GIS to investigate environmental factors correlated with presence of 19 invasive plant species in Vermont campgrounds. My results support the assumption that human dispersal of invasive plant seed and stock may be more important than natural dispersal of these plant species to new sites. I also investigate in-depth the relationships of invasive herbaceous garlic mustard (Alliaria petiolata) with native tree seedlings and co-occurring herbaceous plants in the greenhouse and Vermont forests, respectively. Shade from > 1 m tall A. petiolata plants may effect root:shoot ratios of neighboring tree seedlings and interact with nutrition quality of sites to affect their growth patterns. Invasive plants' integration into novel environments is also mediated by their interactions with native invertebrate species. A. petiolata is associated with a unique assemblage of aboveground invertebrates compared with neighboring native plants. Observations indicate A. petiolata may also serve as an attractant for ants, bees, and wasps who feed from water and nectar at the base of the flower or silique during its flowering and seeding period. These results collectively inform our understanding of plant invasion patterns and management strategies of A. petiolata in Vermont. Community interactions are probably more important than allelopathy in determining the influence of Alliaria petiolata on native ecosystems.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science Degree in Biology (Ecology-track)." "A thesis entitled"--at head of title. Bibliography: leaves 44-55.