As discussed in an earlier post, urban greenspace and biodiversity offers numerous benefits for urbanites. However, not everyone enjoys these benefits equally.
Socioeconomic disparities in urban greenspace and biodiversity are well-documented in many cities, with a growing consensus that these trends present considerable hurdles for urban rewilding efforts.
A stark contrast in tree cover between two areas in Washington: the richer University Place on the left and Tacoma on the right (Source: University of Washington Tacoma)
Unequal exposure to greenspace
Studies around the world have consistently documented a notable correlation between socioeconomic deprivation and greenspace exposure. In Porto, Portugal, researchers noted that the average distance of households to greenspace increased with deprivation. Interestingly, a review of German cities did not find similar inequalities in proximity, instead revealing substantial differences in greenspace area across neighbourhoods with varying income and education levels. In ethnically-diverse cities like London, inequalities in greenspace provision also manifest along racial boundaries. A recent survey found only 39% of non-white respondents living within a five-minute walk of greenspaces, compared to 57% of white respondents.
Spatial distribution of Porto's greenspaces projected onto a map of socioeconomic deprivation (Source: Hoffimann et al. 2017)
Inequality extends beyond mere access to greenspace. Studies of US urban parks showed that the quality of greenspace differed greatly between richer, white areas and poorer, non-white areas. Parks in predominantly non-white neigbourhoods were nearer to sources of pollution, deprived of upgrading, had fewer amenities like nature trails and aesthetic elements, and suffered from more park congestion with higher user density.
These inequalities regained prominence amongst urban scholars when these divisions were exacerbated by the COVID-19 pandemic. Interactions with nature offer a much-needed respite for people under lockdowns. Yet, households in underprivileged neighbourhoods are denied these opportunities, being deprived of quality greenspace in their vicinity and discouraged from travelling out to parks further away.
Furthermore, wealthier families can enjoy nature in private back gardens, a luxury unavailable to many poorer households. In Britain, 1 in 8 households lack access to private gardens during lockdowns, placing these communities at greater risk of mental health issues associated with prolonged isolation.
Public information poster urging the public to only visit parks that are within walking or biking distance (Source: Government of Mercer Island, Washington)
Unequal risks to environmental threats:
The case of "redlining" in the United States
Neighbourhoods deprived of urban nature in turn suffer disproportionately from environmental risks associated with less greenspace and vegetation.
We focus our attention on "redlining", a segregationist practice in the US during the 1930s which rated the risk level of each neighbourhood by the proportion of black and migrant residents. 'Redlined' neighbourhoods were, literally, shaded red on the map, denying them of favourable loan conditions and certain municipal services.
Map by the Home Owners' Loan Corporation in 1937 showing redlining in Oakland (Source: University of California, Berkeley)
This created clusters of poverty across the US, physically imprinting racial discrimination onto the map.
Report: An introduction to 'redlining' in the United States (Source: NPR)
Wealthier white families settled into well-maintained suburbs while underprivileged communities of colour were limited to concretized inner-city areas with poor municipal investment in greening efforts. These communities also lacked the political leverage to resist plans for industrial activity, major roadworks or denser housing near their neighbourhoods - contributing to more anthropogenic heat.
Although redlining was abolished in 1968, its oppressive legacy remains blatantly visible today. A 2020 study found previously redlined areas having around half the canopy cover of majority-white neighbourhoods. With disproportionately less shade and higher anthropogenic heat, these neighbourhoods turn into 'micro' heat-islands. An environmental survey of 108 urban areas across the US revealed that previously redlined neighbourhoods were consistently warmer than non-redlined neighbourhoods. In Portland, inter-neighbourhood differences in surface temperature reached as high as 7'C.
Differences between average city temperature and average neighbourhood temperature for each rating (Source: Portland State University)
These observations are especially pertinent as extreme heat causes more American deaths yearly than any other weather-related phenomenon. Furthermore, this threat is worsening with unabated climate change causing deadlier and more frequent heatwaves.
Besides enhanced heat-island effects, formally redlined neighbourhoods also suffer from more severe pollution and associated health hazards, including higher risks of cancer, respiratory diseases, and weaker infant health. These results corroborate with findings from similar reviews in Europe and on a global scale, highlighting the indisputable correlation between socioeconomic status and pollution exposure.
"People designed (cities), which means that they were designed for particular people, and that means that not everybody was held in mind when plans for cities and communities were made"
Sarah Lillie Anderson, American Forests (Nonprofit organization on tree equity)
Is urban wildlife also drawn along socioeconomic lines?
Socioeconomic disparities etched into urban landscapes shape a corresponding variety of environmental conditions within the city, affecting the spatial distribution of biodiversity.
How systemic racism and residential segregation have a cyclical impact on urban biodiversity (Source: Schell et al. 2020)
The "luxury effect", a hypothesized relationship between household income and species assemblages, has been observed mainly in floral and avian diversity. In South Africa, species richness among urban birds increases with household income throughout various cities. Studies in Phoenix, Arizona, discovered richer bird diversity in greenspaces within wealthier neighbourhoods. Limited studies also apply the luxury effect to explain mesopredator distributions of coyotes and raccoons.
Urban ecologist Christopher Schell further cautions against wider evolutionary implications of systemic segregation. Spatial heterogeneity in vegetation cover and interconnectivity, driven by socio-economic differences, can influence long-term evolutionary patterns of urban wildlife. Fragmentation of greenspace and canopy cover in marginalized communities can inhibit gene flow and genetic diversity of wildlife populations - as observed in New York's white-footed mice. Highways and other manmade structures, more prevalent in poorer neighbourhoods, form potential barriers against inter-population mixing for bumblebees and predators like bobcats and coyotes.
White-footed mouse (Peromyscus leucopus) - where lower canopy cover has been observed to limit gene flow within urban populations
(Source: University of Kentucky)
Disproportionate exposure to pollution and heat-island effects in poorer neighbourhoods may also create selection pressures that influence evolution trajectories. Despite no explicit evidence linking environmental heterogeneity from systemic segregation to adaptive evolution, entomologists observed increased thermal endurance in urban arthropods from ants to damselflies compared to rural counterparts -- trends potentially reflected in intra-city temperature variations. Higher exposure to pollutants, however, caused higher rates of unfavourable genetic mutations in mice, suggesting adverse evolutionary consequences of increased pollution in segregated neighbourhoods on wildlife.
Interview: Christopher Schell, Assistant Professor of Urban Ecology at University of Washington Tacoma, explains how social inequality impact the distribution and health of urban wildlife (Source: The News Tribune)
Rethinking the way we look at urban nature
Seeing how societal inequalities are inextricably woven into urban ecology, there is a need to re-evaluate our scientific approach for examining urban biodiversity.
Schell notes how most research on urban ecology, intentionally or otherwise, focus on richer neighbourhoods with higher vegetation cover and lower pollution - which may perpetuate the oversight of how systemic inequality impacts urban biodiversity.
"That means fundamentally changing how researchers do their science, which questions they ask, and realizing that their usual set of questions might be incomplete."
Christopher Schell, Assistant Professor of Urban Ecology
University of Washington Tacoma
Advocates and scholars in environmental justice must hence integrate an understanding of how historical legacies of systemic racism manifest spatially through the built environment, and integrate this perspective into current practices of socio-ecological research. Attempting to comprehend urban ecology without appreciating these underlying socioeconomic structures permeating through our cities would be myopic and unwise.
With this added socioeconomic lens, planners and scientists can endeavour towards including these marginalized voices when shaping policy for wider ecological goals.
If you are interested in the latest research on how systemic racism and classism affects urban wildlife, I recommend following Christopher Schell on Twitter. He regularly posts updates on his work and other interesting news about urban biodiversity.
(Source: Grit City Carnivore Project)
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