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The phyllosphere of Phoenix's urban forest: insights from a publicly-funded microbial environment

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The aboveground surfaces of plants (i.e. the phyllosphere) comprise the largest biological interface on Earth (over 108 km2). The phyllosphere is a diverse microbial environment where bacterial inhabitants have been

The aboveground surfaces of plants (i.e. the phyllosphere) comprise the largest biological interface on Earth (over 108 km2). The phyllosphere is a diverse microbial environment where bacterial inhabitants have been shown to sequester and degrade airborne pollutants (i.e. phylloremediation). However, phyllosphere dynamics are not well understood in urban environments, and this environment has never been studied in the City of Phoenix, which maintains roughly 92,000 city trees. The phyllosphere will grow if the City of Phoenix is able to achieve its goal of 25% canopy coverage by 2030, but this begs the question: How and where should the urban canopy expand? I addressed this question from a phyllosphere perspective by sampling city trees of two species, Ulmus parvifolia (Chinese Elm) and Dalbergia sissoo (Indian Rosewood) in parks and on roadsides. I identified characteristics of the bacterial community structure and interpreted the ecosystem service potential of trees in these two settings. I used culture-independent methods to compare the abundance of each unique bacterial lineage (i.e. ontological taxonomic units or OTUs) on the leaves of park trees versus on roadside tree leaves. I found numerous bacteria (81 OTUs) that were significantly more abundant on park trees than on roadside trees. Many of these OTUs are ubiquitous to bacterial phyllosphere communities, are known to promote the health of the host tree, or have been shown to degrade airborne pollutants. Roadside trees had fewer bacteria (10 OTUs) that were significantly more abundant when compared to park trees, but several have been linked to the remediation of petroleum combustion by-products. These findings, that were not available prior to this study, may inform the City of Phoenix as it is designing its future urban forests.

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Date Created
  • 2016

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Ecology and the city: a long-term social-ecological examination of the drivers and diversity of urban vegetation

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Often, when thinking of cities we envision designed landscapes, where people regulate everything from water to weeds, ultimately resulting in an ecosystem decoupled from biophysical processes. It is unclear, however,

Often, when thinking of cities we envision designed landscapes, where people regulate everything from water to weeds, ultimately resulting in an ecosystem decoupled from biophysical processes. It is unclear, however, what happens when the people regulating these extensively managed landscapes come under stress, whether from unexpected economic fluctuations or from changing climate norms. The overarching question of my dissertation research was: How does urban vegetation change in response to human behavior? To answer this question, I conducted multiscale research in an arid urban ecosystem as well as in a virtual desert city. I used a combination of long-term data and agent-based modeling to examine changes in vegetation across a range of measures influenced by biophysical, climate, institutional, and socioeconomic drivers. At the regional scale, total plant species diversity increased from 2000 to 2010, while species composition became increasingly homogeneous in urban and agricultural areas. At the residential scale, I investigated the effects of biophysical and socioeconomic drivers – the Great Recession of 2007-2010 in particular – on changing residential yard vegetation in Phoenix, AZ. Socioeconomic drivers affected plant composition and increasing richness, but the housing boom from 2000 through 2005 had a stronger influence on vegetation change than the subsequent recession. Surprisingly, annual plant species remained coupled to winter precipitation despite my expectation that their dynamics might be driven by socioeconomic fluctuations. In a modeling experiment, I examined the relative strength of psychological, social, and governance influences on large-scale urban land cover in a desert city. Model results suggested that social norms may be strong enough to lead to large-scale conversion to low water use residential landscaping, and governance may be unnecessary to catalyze residential landscape conversion under the pressure of extreme drought conditions. Overall, my dissertation research showed that urban vegetation is dynamic, even under the presumably stabilizing influence of human management activities. Increasing climate pressure, unexpected socioeconomic disturbances, growing urban populations, and shifting policies all contribute to urban vegetation dynamics. Incorporating these findings into planning policies will contribute to the sustainable management of urban ecosystems.

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Date Created
  • 2015

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Designing and implementing ecological monitoring of aridland urban ecological infrastructure (UEI): a case-study of design process and outcomes

Description

Cities are increasingly using nature-based approaches to address urban sustainability challenges. These solutions leverage the ecological processes associated with existing or newly constructed Urban Ecological Infrastructure (UEI) to address issues

Cities are increasingly using nature-based approaches to address urban sustainability challenges. These solutions leverage the ecological processes associated with existing or newly constructed Urban Ecological Infrastructure (UEI) to address issues through ecosystem services (e.g. stormwater retention or treatment). The growing use of UEI to address urban sustainability challenges can bring together teams of urban researchers and practitioners to co-produce UEI design, monitoring and maintenance. However, this co-production process received little attention in the literature, and has not been studied in the Phoenix Metro Area.

I examined several components of a co-produced design process and related project outcomes associated with a small-scale UEI project – bioswales installed at the Arizona State University (ASU) Orange Mall and Student Pavilion in Tempe, AZ. Specifically, I explored the social design process and ecohydrological and biogeochemical outcomes associated with development of an ecohydrological monitoring protocol for assessing post-construction landscape performance of this site. The monitoring protocol design process was documented using participant observation of collaborative project meetings, and semi-structured interviews with key researchers and practitioners. Throughout this process, I worked together with researchers and practitioners to co-produced a suite of ecohydrological metrics to monitor the performance of the bioswales (UEI) constructed at Orange Mall, with an emphasis on understanding stormwater dynamics. I then installed and operated monitoring equipment from Summer 2018 to Spring 2019 to generate data that can be used to assess system performance with respect to the co-identified performance metrics.

The co-production experience resulted in observable change in attitudes both at the individual and institutional level with regards to the integration and use of urban ecological research to assess and improve UEI design. My ecological monitoring demonstrated that system performance met design goals with regards to stormwater capture, and water quality data suggest the system’s current design has some capacity for stormwater treatment. These data and results are being used by practitioners at ASU and their related design partners to inform future design and management of UEI across the ASU campus. More broadly, this research will provide insights into improving the monitoring, evaluation, and performance efficacy associated with collaborative stormwater UEI projects, independent of scale, in arid cities.

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Date Created
  • 2019