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Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC Santa Cruz Electronic Theses and Dissertations (2019)

This dissertation examines the local and landscape drivers of biodiversity, ecosystem service provisioning and human well-being in urban agricultural systems (agroecosystems). I explore three major themes: 1) urban biodiversity and ecosystem services; 2) climate change, water management and sustainability; and 3) urban gardens as socioecological systems. In an interdisciplinary approach, I use quantitative and qualitative methods in natural and social systems.

In the first section, I examine the local and landscape scale drivers of biodiversity and pest control within urban gardens. I focus on the abundance and species richness of ladybird beetles – an important and mobile natural enemy of garden pests. I measure ladybeetle diversity within gardens, and experimentally test factors predicted to influence ladybeetle fidelity to gardens. I find that ladybeetle dispersal is higher from gardens in more impervious landscapes, albeit overall high taxonomic richness supported by these habitats. In comparison to other contexts, these results may be unique to California due to water availability maintained through garden irrigation.

In the second section, I investigate how gardens become irrigated oases in an otherwise drought landscape. I use citizen science to collect water use data and ask how environmental concern and water governance are affecting water use behavior by gardeners. I also investigate how climate variability and increasing extremes influence water management and plant species cultivated in gardens. I find that gardeners lack an understanding of water use, are responding to weather patterns by changing watering behavior, and that garden rules can limit water use. Moreover, research participation can improve gardeners’ water conservation literacy. This work informs our understanding of how climate change may impact urban agriculture sustainability and alludes to the socioecological complexity of gardens.

In the third section, I focus on the social aspects of urban gardens and their management. I show that gardens provide many well-being benefits to gardeners, and are used more by people in urban areas. Yet I explain that there are crucial issues that undermine social and ecological sustainability in these gardens: the resources that create a habitat for biodiversity dually create social-political rifts within gardener communities. Gardens, and their biophysical and social elements, are relatively novel in the scope of contemporary land use transformations.

In summary, I show that urban gardens are sites of biodiversity, climate challenges, and social-ecological complexity that add to urban novelty. Using our understanding of complexity can inform management to improve urban and agricultural sustainability.

  • 11 supplemental PDFs
Cover page: Local and Landscape Drivers of Biodiversity, Ecosystem Services, and Human Well-being in Urban AgroecosystemsCreative Commons 'BY-NC-SA' version 4.0 license
  • Article
  • Peer Reviewed
UC Santa Cruz Previously Published Works (2018)
    Cover page: Cityscape quality and resource manipulation affect natural enemy biodiversity in and fidelity to urban agroecosystems
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2018)
      Cover page: Gardener Well-Being along Social and Biophysical Landscape Gradients
      • Article
      • Peer Reviewed
      UC Santa Cruz Previously Published Works (2020)
      Ecological networks can provide insight into how biodiversity loss and changes in species interactions impact the delivery of ecosystem services. In agroecosystems that vary in management practices, quantifying changes in ecological network structure across gradients of local and landscape composition can inform both the ecology and function of productive agroecosystems. In this study, we examined natural-enemy-herbivore co-occurrence networks associated with Brassica oleracea (cole crops), a common crop in urban agricultural systems. Specifically, we investigated how local management characteristics of urban community gardens and the landscape composition around them affect (1) the abundance of B. oleracea herbivores and their natural enemies, (2) the natural-enemy : herbivore ratio, and (3) natural-enemy-herbivore co-occurrence network metrics. We sampled herbivores and natural enemies in B. oleracea plants in 24 vegetable gardens in the California, USA central coast region. We also collected information on garden characteristics and land-use cover of the surrounding landscape (2 km radius). We found that increased floral richness and B. oleracea abundance were associated with increased parasitoid abundance, non-aphid herbivore abundance, and increased network vulnerability; increased vegetation complexity suppressed parasitoid abundance, but still boosted network vulnerability. High agricultural land-use cover in the landscape surrounding urban gardens was associated with lower predator, parasitoid, and non-aphid herbivore abundance, lower natural-enemy : herbivore ratios, lower interaction richness, and higher trophic complementarity. While we did not directly measure pest control, higher interaction richness, higher vulnerability, and lower trophic complementarity are associated with higher pest control services in other agroecosystems. Thus, if gardens function similarly to other agroecosystems, our results indicate that increasing vegetation complexity, including trees, shrubs, and plant richness, especially within gardens located in intensively farmed landscapes, could potentially enhance the biodiversity and abundance of natural enemies, supporting ecological networks associated with higher pest control services.
        Cover page: Natural enemy–herbivore networks along local management and landscape gradients in urban agroecosystems
        • Article
        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2019)
        Urban ecosystems, as mosaics of residential, industrial, commercial, and agricultural land, present challenges for species survival due to impervious surface, degradation, fragmentation, and modification of natural habitat, pollution, and introduced species. Some urban habitats, such as community gardens, support biodiversity and promote ecosystem services. In gardens, local factors (e.g., vegetation, groundcover) and landscape surroundings (e.g., agriculture, built or impervious cover) may influence species abundance, richness, and functional traits that are present. We examined which local and landscape factors within 19 community gardens in the California central coast influence ground beetle (Carabidae) activity density, species richness, functional group richness, and functional traits-body size, wing morphology, and dispersal ability. Gardens with higher crop richness and that are surrounded by agricultural land had greater carabid activity density, while species and functional group richness did not respond to any local or landscape factor. Gardens with more leaf litter had lower carabid activity, and gardens with more leaf litter tended to have more larger carabids. Changes in local (floral abundance, ground cover) and landscape (urban land cover) factors also influenced the distribution of individuals with certain wing morphology and body size traits. Thus, both local and landscape factors influence the taxonomic and functional traits of carabid communities, with potential implications for pest control services that are provided by carabids.
          Cover page: Local and Landscape Drivers of Carabid Activity, Species Richness, and Traits in Urban Gardens in Coastal California.
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2018)
            Cover page: Herbivore regulation in urban agroecosystems: Direct and indirect effects
            • Article
            • Peer Reviewed
            UC Santa Cruz Previously Published Works (2018)
            Urban gardens are vital green spaces, providing food for residents and space for engaged citizenry and community development. In California, climate change conditions (heat and drought) are becoming more extreme, threatening the resilience of urban gardens. Water use restrictions limit the timing and amount of water that gardeners can access, exacerbating these climate challenges for urban food production. Together with volunteer gardeners, we examined how ambient temperature, water use, vegetation, ground cover, and soil management affect rates of soil moisture gain and loss in urban gardens for a six-week period in the summer of 2017, during the hottest part of the growing season. We found that plot-level management of soils is essential for creating urban garden plots that maintain stable levels of water within garden soils. Although plots with better soil quality (i.e. water holding capacity) experienced slower rates of soil moisture gain after a watering event, they also experienced slower rates of soil moisture loss after the event, leading to soils with more stable, less fluctuating moisture profiles over time. This may benefit gardeners because under extreme climates (such as heat and drought) and water use restrictions, maintaining more stable soils for their plants means that the soils will retain water over a longer period after each watering event. Overall, such results highlight that better soil management that improves soil quality measures such as water holding capacity are potential solutions for maintaining soil moisture and reducing water use under changing climate conditions.
              Cover page: Soil management is key to maintaining soil moisture in urban gardens facing changing climatic conditions
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2022)
              Gardening has the potential to improve health and wellbeing, especially during crises. Using an international survey of gardeners (n = 3743), this study aimed to understand everyday gardening experiences, perspectives and attitudes during early stages of the COVID-19 pandemic in 2020. Our qualitative reflexive thematic and sentiment analyses show that during the first months of the COVID-19 pandemic, gardening seemed to create a safe and positive space where people could socially connect, learn and be creative. Participants had more time to garden during the pandemic, which led to enhanced connections with family members and neighbours, and the ability to spend time in a safe outdoor environment. More time gardening allowed for innovative and new gardening practices that provided enjoyment for many participants. However, our research also highlighted barriers to gardening (e.g. lack of access to garden spaces and materials). Our results illustrate the multiple benefits of gardening apparent during COVID-19 through a lens of the social-ecological model of health.
                Cover page: Experiences of gardening during the early stages of the COVID-19 pandemic
                • Article
                • Peer Reviewed
                UC Santa Cruz Previously Published Works (2022)
                Cities are sometimes characterized as homogenous with species assemblages composed of abundant, generalist species having similar ecological functions. Under this assumption, rare species, or species observed infrequently, would have especially high conservation value in cities for their potential to increase functional diversity. Management to increase the number of rare species in cities could be an important conservation strategy in a rapidly urbanizing world. However, most studies of species rarity define rarity in relatively pristine environments where human management and disturbance is minimized. We know little about what species are rare, how many species are rare, and what management practices promote rare species in urban environments. Here, we identified which plants and species of birds and bees that control pests and pollinate crops are rare in urban gardens and assessed how social, biophysical factors, and cross-taxonomic comparisons influence rare species richness. We found overwhelming numbers of rare species, with more than 50% of plants observed classified as rare. Our results highlight the importance of women, older individuals, and gardeners who live closer to garden sites in increasing the number of rare plants within urban areas. Fewer rare plants were found in older gardens and gardens with more bare soil. There were more rare bird species in larger gardens and more rare bee species for which canopy cover was higher. We also found that in some cases, rarity begets rarity, with positive correlations found between the number of rare plants and bee species and between bee and bird species. Overall, our results suggest that urban gardens include a high number of species existing at low frequency and that social and biophysical factors promoting rare, planned biodiversity can cascade down to promote rare, associated biodiversity.
                  Cover page: Rarity begets rarity: Social and environmental drivers of rare organisms in cities
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