Landscape Architecture Theses and Dissertations

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Browsing Landscape Architecture Theses and Dissertations by Author "Johnson, Bart"

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    Identifying Landtype Phases for Oregon White Oak Restoration in the Willamette National Forest, Oregon
    (University of Oregon, 2022-10-04) Kurtz, Lindsey; Johnson, Bart
    Ecological classification systems are used to understand and restore complex heterogeneous landscapes. We explored an ecological classification methodology to determine fine-grained land units by combining field and remote sensing data. Regression trees were used to create these land units, which we term landtype phases. Oregon white oak was chosen as a test case for the methodology because of its conservation importance, the paucity of knowledge about how to sustain it in heterogeneous landscapes, and its wide range of growing conditions. We identified two landtype phases, the moist margins of harsh meadows and cooler locations away from the meadows. The fieldwork-based variables used to identify and classify these landtype phases were translated into remote-sensing variables using LiDAR, which allowed landtype phase mapping. Our results demonstrate how an integration of field-based and LiDAR-based approaches can provide useful guidance for restoration while highlighting the need for improved translation among the two data types.This thesis includes unpublished co-authored material.
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    Investigating Forest Elephant Crop Depredation to Guide Landscape Management for Villager-Elephant Coexistence
    (University of Oregon, 2023-03-24) Memiaghe, Herve Roland; Johnson, Bart
    Forest elephant destruction of villagers' crops in and around Gabon's national parks has persisted despite intensive efforts to control the problem by blocking elephant access to crops. I developed an alternative approach to craft spatially integrated landscape management strategies that simultaneously meet the needs of villagers and elephants, which I call a landscape framework for human-elephant coexistence. To craft the coexistence framework, I investigated factors influencing CDIs in two villages at Lopé National Park, Gabon. In chapter 2, I used content analysis of semi-structured interviews with 46 villagers and conservation professionals to explore how interacting landscape processes lead to CDIs. This generated a conceptual framework characterizing how six broadscale CDI drivers set in motion five landscape change dynamics, which in turn lead to five generalizable problem types that directly contribute to CDIs in village areas. In chapter 3, I combined the stakeholder interviews with a mapped census of native fruit tree distribution along elephant trails in the two villages and nearby forest, and long-term fruit phenology data to assess CDI distribution in relation to seasonal availability of native fruits and domestic crops. The results indicate that neither crop nor native fruit availability, nor the interaction between them, is a definitive factor controlling CDIs. Instead, they suggest that the spatial and temporal distribution of elephant resources and human activities within mosaics of natural and managed landscapes combine to influence elephant foraging behaviors, which in turn set the stage for CDIs. In chapter 4, I reframed each of the five problem types into a coexistence strategy, and identified a toolbox of 59 actions to form the core of the landscape coexistence framework, and used chapter three results to inform how strategies could be applied at local extents. Two of the five strategies were targeted to fulfilling elephant needs, two toward villager needs, and one toward reducing the spatial overlap of elephant foraging and villager cropping activities. The landscape coexistence framework serves as an overarching structure through which participatory planning could be conducted at the scale of individual villages or an entire national park like Lopé.
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    Protecting Stream Ecosystem Health in the Face of Rapid Urbanization and Climate Change
    (University of Oregon, 2015-01-14) Wu, Hong; Johnson, Bart
    The ability to anticipate and evaluate the combined impacts of urbanization and climate change on streamflow regimes is critical to developing proactive strategies that protect aquatic ecosystems. I developed an interdisciplinary modeling framework to compare and contrast the effectiveness of integrated stormwater management, or its absence, with two regional growth patterns for maintaining streamflow regimes in the context of climate change. In three adjacent urbanizing watersheds in Oregon's Willamette Valley, I conducted a three-step sequence to: 1) simulate land use change under four future development scenarios with the agent-based model Envision; 2) model resultant hydrological change under the recent past and two future climate regimes using the Soil and Water Assessment Tool; and 3) assess scenario impacts on streamflow regimes using 10 ecologically significant flow metrics. I evaluated each scenario in each basin using a flow metric typology based on the magnitude of change in each metric and the degree to which such changes could be mitigated, i.e., insensitive, sensitive and manageable, and sensitive and resistant. My results demonstrated distinct signatures of urbanization and climate change on flow regimes. Urbanization and climate change in isolation led to significant flow alterations in all three basins. Urbanization consistently led to increases in flow regime flashiness and severity of extreme flow events, whereas climate change primarily caused a drying trend. Climate change tended to exacerbate the impacts of urbanization but also mitigated urban impacts on several metrics. The combined impacts of urbanization and climate change caused substantial changes to metric sensitivities, which further differed by basin and climate regime, highlighting the uncertainties of streamflow regime responses to development and the value of spatially explicit modeling that can reveal complex interactions between natural and human systems. Scenario comparisons demonstrated the importance of integrated stormwater management and, secondarily, compact regional growth. My findings reveal the need for regional flow-ecology research that substantiates the ecological significance of each flow metric, develops specific targets for manageable ones, and explores potential remedies for resistant ones. The interdisciplinary modeling framework shows promise as a transferable tool for local watershed management. This dissertation includes previously unpublished co-authored material.
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    Relationships Among Airborne Microbial Communities, Urban Land Uses and Vegetation Cover: Implications for Urban Planning and Human Health
    (University of Oregon, 2018-09-06) Mhuireach, Gwynne A.; Johnson, Bart
    Variation in exposure to environmental microbial communities has been implicated in the etiology of allergies, asthma and other chronic and immune disorders. In particular, preliminary research suggests that exposure to a high diversity of microbes during early life, for example through living in highly vegetated environments like farms or forests, may have specific health benefits, including immune system development and stimulation. In the face of rapidly growing cities and potential reductions in urban greenspace, it is vital to clarify our understanding of the relationship between vegetation and microbial communities so that we can better design cities that support human health. To explore whether and how urban airborne bacterial communities vary with the amount and structural diversity of nearby vegetation, I used passive air sampling and culture-independent microbial DNA sequencing combined with more traditional landscape architecture tools, including geographic information systems (GIS) and remote sensing data. The results indicated that locations with little vegetation (i.e., paved parking lots) were marked by significantly different bacterial composition from areas that were heavily vegetated (parks and forests). These differences were largely driven by taxonomic groups and indicator species that were enriched at certain sites. My work also shows that regional agricultural activities during the summer may have a substantial effect on airborne bacterial communities in the Eugene-Springfield metropolitan area (Oregon), specifically through elevated abundance of Sphingomonas faeni, a taxon previously isolated from hay dust. The second part of my work focused on building a conceptual bridge between scientific findings and potential design principles that can be tested in practical application. I performed a narrative review of vegetation-health, vegetation-microbe, and microbe-health relationships, which formed the foundation of a framework to translate scientific findings into design-relevant concepts. Strengthening this linkage between science and design will help ensure that research questions are relevant to design practice and that new scientific knowledge is accessible to designers. This dissertation includes previously published and unpublished co-authored material.
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    Spatial Patterns and Management Implications of Native Bunchgrass Recovery Following Oak-Pine Savanna Restoration in the Mid-Elevation Oregon Cascades
    (University of Oregon, 2022-10-04) Horton, Eyrie; Johnson, Bart
    Restoring native grasslands by counteracting the forest succession which followed the loss of historical fire regimes is a vital component of landscape management in the Mediterranean moist climate of the western Pacific Northwest, USA. However, canopy cover reduction alone does not assure healthy grassland regeneration. Site-specific and species-level research is needed to identify effective restoration strategies. I examined two native bunchgrasses, Festuca roemeri and Festuca californica, in the Jim’s Creek Restoration Area (Jim’s Creek) to assess their relative success across varying microenvironmental and competitive gradients prior to and following restoration. To make these findings more accessible, I developed a handbook that employs a graphic language to make scientific research findings accessible to land managers and those who may not have a background reading statistics-based, ecological literature. This thesis includes unpublished co-authored material.