Browsing by Subject "Urban forest"
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Item Open Access America’s Evolving Relationship with Trees: A Statistical Analysis of Social, Economic, and Environmental Drivers of Forest Management(2021) Holt, JonathanIn the spirit of American individualism, the majority of the United States’ forested landscape is controlled by private landowners, who make autonomous decisions that impact a shared wealth of biodiversity and ecosystem services. It is important to understand not only the forest management decisions made by private landowners, but also the motivations that incentivize these consequential actions. Furthermore, it is useful to have the capacity to infer such insights using publicly available data, and by employing transparent, flexible, and scalable statistical frameworks. This dissertation seeks to elucidate the motivations and actions of private landowners in the United States using a variety of data sources, including Zillow home estimates, the American Community Survey, satellite remote sensing imagery, and the Forest Inventory and Analysis database, and by implementing interpretable modeling frameworks, such as the hedonic pricing method and structural equation modeling. I uncover nuanced insights about human-environmental systems, including (1) a positive feedback loop between affluence and tree-shading in metropolitan areas; (2) the dominance of normative pressures on forest owners’ harvest intentions; and (3) a causal link between invasive insects and the quantity and sizes of harvested trees. Understanding such relationships benefits policymakers, forest managers, and urban planners tasked with optimizing human-natural systems.
Item Open Access Legacy Pb contamination in the soils of three Durham city parks: Do secondary forest organic horizons effectively blanket Pb in city park soils contaminated by historic waste incineration?(2022-12-16) Bihari, EnikoeLead (Pb) has historically been used in many products such as gasoline, paint, batteries, ceramics, pipes and plumbing, solders, and cosmetics, and Pb contamination from these materials and their waste streams is widespread around the world. Pb is a highly insoluble and persistent contaminant that accumulates in the environment, especially in urban soils; to this day, soil Pb concentrations remain high in many cities, posing a significant long-term public health and environmental risk. Some remediation options are available for Pb, with the most effective being removal and replacement of the contaminated soil. However, plants that can tolerate soil Pb may be effective at phytostabilization. In phytostabilization, soil Pb is immobilized both physically and chemically by the roots, while also being sequestered by new layers of organic matter and soil that accumulate on the surface. Throughout the early 1900s, the city of Durham, NC operated neighborhood municipal incinerators which combusted most of the city’s waste, including waste collected from homes, businesses, and public street cleaning. Around 1950, the four of the incinerator sites were closed and converted into public parks, with playgrounds, grass fields, picnic benches, sports facilities, and walking paths. These are now Walltown, East End, East Durham, and Lyon Parks. The parks currently contain streams and large areas of secondary forest cover, which have been largely unmanaged throughout the last century. From local newspaper articles, we have direct evidence for the disposal of incinerator refuse at these sites and other Durham parks. While historic news accounts describe the incinerator sites being covered with topsoil, until this study there has been no monitoring of the status of contaminant metals in the soils throughout the parks. We hypothesized that the surface soils of these parks had elevated Pb concentrations as the result of the parks’ history of incineration. Our primary objectives were to: 1. Measure total mineral surface soil Pb concentrations across three of Durham’s urban parks which were historically used for waste incineration (Walltown, East End, and East Durham Parks). 2. Assess whether secondary hardwood forests have accumulated organic horizons that were effective barriers to Pb-contaminated mineral soil below. We sampled mineral surface soil and organic horizon according to a stratified random sampling design, and the samples were measured for total Pb with an Olympus Vanta pXRF instrument. Data were analyzed using R and ArcGIS Pro, resulting in statistical models and spatial interpolations. Our main results were: 1. Mineral soil Pb concentrations across Walltown, East End, and East Durham Parks are elevated above both geologic background levels and several EPA hazard thresholds, especially in some highly-trafficked areas. 2. Hardwood forest organic horizons provide a blanket for highly Pb-contaminated mineral soil, but a significant amounts of surface soil Pb is mixed up into these O horizons. Thus, exposure risk is not eliminated and can remain quite high. Our results show that all three parks have total Pb in surface soils (0-2.5 cm) well above the geologic background (0-30 ppm), with many soils exceeding the US EPA’s hazard thresholds for gardening (100 ppm), residential play areas (400 ppm), and residential non-play areas (1200 ppm). For all three parks combined, mineral soil Pb ranged from 8 to 2342 ppm, with a mean of 201 ppm and a median of 93 ppm. A notable hotspot with extremely high Pb was mapped throughout the southeastern portion of East Durham Park north of East Main St., spanning a grassy field and part a secondary forest (Figure 12). Mineral soil Pb in this hotspot ranged from 694 to 2342 ppm. This is of particular concern because this field is adjacent to an apartment building, and residents appear to use this area to play, garden, and park their cars. Additionally, our study demonstrates that while hardwood O horizons provide a physical barrier to exposure for highly contaminated mineral soil, a significant amount of mineral soil Pb is mixed up into the O horizons. This relationship differed significantly between the upper O1/O2 and the lower O3 horizons. Pb concentration in the lower O3 horizon increased by 0.6 ppm for every 1 ppm increase in Pb increase in the mineral soil, with an adjusted R2 of 0.86. This means that the lower O3 horizon has about 60% of the Pb concentration of the mineral soil below. In contrast, Pb concentration in the upper O1/O2 horizon increased by 0.1 ppm for every 1 ppm increase in Pb increase in the mineral soil, with an adjusted R2 of 0.49. This means that the upper O1/O2 horizons have about 10% of the Pb concentration of the mineral soil below, Our results suggest limitations to phytostabilization as tool to reduce Pb exposure, particularly in hardwood forests where there is relatively rapid decomposition and bioturbation in the O horizons compared to many coniferous forests. Overall, the spatial distribution of soil Pb concentrations demonstrates the complicated land use history of these landscapes, pointing towards multiple sources of Pb inputs and outputs throughout the 20th century. Based on articles in historic newspapers from five cities across the USA, many municipalities may have public parks converted from historic waste incinerator sites; these sites may be contaminated with Pb and other metals that would have accumulated in ash and cinders, posing an exposure risk to residents who visit the parks.Item Open Access Planning a Sustainable Tree Canopy for Durham(2020-04-24) Hancock, Grace; Vanko, Alex; Xiong, MingfeiTrees are a vital part of a city’s infrastructure. The urban forest provides many ecosystem services to residents including health benefits, air pollution removal, extreme heat reduction, stormwater mitigation, and even lower violent crime rates. Durham, North Carolina is 52% covered by trees, but its canopy is declining from urban development, and it is unevenly distributed due to a history of racial and socioeconomic inequity. Parts of the city that are more urbanized, non-white, and poor tend to have far less tree cover than more rural, white, affluent areas. This Masters Project sought to help TreesDurham and the City of Durham plan a sustainable tree canopy that meets the city’s goal of 55% cover by 2040. Expansion of Durham’s urban forest must address the concerns of the community, maximize ecosystem services, and consider possible changes to city development codes. We addressed these needs by (1) conducting a community survey to understand Durham residents’ attitudes towards city trees, (2) creating a tree-planting prioritization map based on ecosystem services, and (3) modeling the future of Durham’s urban forest under multiple development scenarios. We recommend that TreesDurham and the City of Durham (1) incorporate input from Durham residents, (2) target tree-planting to the areas that need tree ecosystem services the most, including heavily urbanized areas and roadside rights-of-way, and (3) greatly increase tree protection requirements in Durham’s development code. This will ensure that all residents of Durham enjoy access to the benefits of the urban forest.Item Embargo Urban Tree Stress in Socio-Ecological Systems(2024) Poulton Kamakura, RenataUrban trees provide crucial ecosystem services for cities, and their health impacts how effectively they provide those ecosystem services. Urban areas present stressful conditions for trees that depend on social as well as biophysical conditions. Despite their importance, patterns of non-lethal tree stress are rarely studied in cities. Although some tree care practices are effective, the influence of the underlying socio-ecological context is poorly understood. In this dissertation, I use a literature review, field data collection, and remote sensing to assess: 1) which tree care practices are effective in mediating tree stress in urban areas and what elements of the socio-ecological context impact their effectiveness 2) how tree-level characteristics, site conditions, and tree care practices correlate to street tree stress, 3) what socio-demographic characteristics and patterns of construction are associated with street tree stress across neighborhoods, and 4) how added climatic stress from drought impacts urban trees. Analysis includes two cities (Chicago and Durham), which offer contrasts in city layout, density, climate, and historical development. When examined across neighborhoods with field data, the few tree care practices examined (mulching, pruning, landscaping) do not reduce stress for urban street trees. Despite the differences between the cities studied, urban tolerant trees consistently have lower stress. In both cities planting site type and land use can influence tree stress levels. Scaled up to a regional level, tree stress is higher in areas with more new building construction and fewer renovations or additions. Drought does not appear to differentially impact trees depending on land use or nearby construction. The relationship between tree stress and urban growing conditions is visible across scales and contexts, but some of the specific relationships, including the effectiveness of tree care practices, are more context specific.