2019 UWT GIS Certificate Capstone Project
Ecology-Forward Urban Planning
Is Single Family Residential Still the American Dream?
As a sustainable urban development major, I have become passionate about community-oriented development with a focus on improving local ecology. With the larger threat of climate change and rapid urbanization, cities are both the problem and the answer for future generations.
Pedestrian-friendly and mixed-use development are often pitched as the leading form of sustainable cities. Inspired both because of, and in spite of, revolutionary authors such as Jane Jacobs and Le Corbusier, I wanted to dive into what the ecology of the built environment looks like in our own backyard.
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The discourse of the urban environment has come to a decision point: to uphold urban legacies the
modern environment evolved from through status-quo decision making, or to create the nature we want
to see and generate more productive environments. Urban form matters. It significantly impacts our
mental and physical wellbeing, and dictates the pervasive perception of normalcy for future generations
(Cronon, 1995). The field of urban political ecology has been gaining traction over the last few decades
in urban planning, and its scholars express that ecological and social processes are not separate, but
integrated (Heynen et. al, 2006). As world urbanization continues to increase, it is essential to begin
implementing strategies that enable us to live with nature now, rather than resulting to ornamental and
ineffective landscapes.
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To produce the next generation of urban development, identifying the areas needing improvement is the first step. In Pierce County, where are we creating the most ecologically functional environments? In addition, what land use designations are associated with hot spots of ecological function and ecological deprivation?
From urban political ecology literature and data availability, the following factors were included in analyzing the ecology of Pierce County: tree canopy density, impervious surface density, and groundwater nitrate levels. Urban trees reduce heat island effects, decrease pollution and erosion, and increase biodiversity. Impervious surfaces significantly contribute to pollution and nutrient loading, and change the geomorphology of steams. Nitrates found in water are anthropogenically elevated from pollution, fertilizers, land conversion, and much more. The limit for nitrogen in public water systems is currently 10 mg/L (Morgan, 2016).
Creating an ecology index was the first step in this analysis. Canopy density and impervious surface density were gathered from 2011 USGS National Land Cover Database data and reclassified (Figure 1 and Figure 3). To prepare a
groundwater nitrate level layer, Pierce county well locations and nitrate priority area polygons were taken from the Washington State Department of Ecology. Nitrate excedances in groundwater were also utilized from the Washington State Department of Health. Well locations were given water quality designations ranging from 1 to 13 (an estimated approximation of mg/L) based on their relationship to known nitrate data using a spatial join. With Kriging interpolation, nitrate values could be estimated between well locations (Figure 2). Using the raster calculator, all three variables were added together to create the ecology index. The nitrate level layer was given a quotient of 0.75 to accommodate generalizations made during the analysis.
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Land use policies are not homogeneous across jurisdictions, so the scale of analysis was narrowed to the cities of Tacoma and Puyallup. Zonal statistics were calculated using the ecology index and land use designations of each city. This produced an ecology ‘score’ for each polygon. To better visualize the ecology-land use relationship, a hot spot analysis was run using the zone of indifference spatial conceptualization. For Tacoma, the threshold of indifference was set to 2964 feet, and the threshold for Puyallup was 1128 feet. The distances of analysis were verified with Morans Spatial Autocorrelation, and the differences reflect the different size and spatial relationships in each city,
respective The hot spot analysis was spatially joined to individual tax parcels, and the specifics of residential and commercial land uses were compared.
From an initial glance, ecologically deprived areas are largely concentrated in the Tacoma urban metropolitan region. The best ecology had a low value of 3, and the worst, a value of 21. Diving into a much finer scale of analysis, Tacoma ecology scores ranged from 17-19. Low density and high density residential land use had almost identical ecology, but low density ultimately scored the best. Commercial land uses were also similar across the board, but general commercial scored the best, given its Z-Score.
In Puyallup, low, moderate, and high density were ranked best to worst, although moderate density was found insignificant (p > 0.05). Auto-oriented commercial had the best ecology score, followed by limited commercial.
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Given that accurately measuring ecology is difficult to define, and some influential variables were unaccounted for such as soil toxicity, this analysis serves as a broad spatial pattern of local ecology in Pierce County as it relates to urban development. Prioritizing ecology looks different depending on a city’s unique history and characteristics. High density residential is producing some of the most ecologically-sound environments in Tacoma, while single family residential is still the American dream in Puyallup.
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Sources
​Cronon, W. (1995). Uncommon Ground: Rethinking the Human Place in Nature. New York: W.W. Norton.
Heynen, N., Kaika, M., and Swyngedouw, E. (2006). Urban Political Ecology, from In the Nature of Cities, Routledge.
Morgan, L. (2016, May). Washington Nitrate Priority Project (Rep. No. 16-10-011). Retrieved from https://fortress.wa.gov/ecy/publications/documents/1610011.pdf