Residential Housing Segregation and Urban Tree Canopy

Research Issue

Leafy Pine Street in Center City is contrasted with treeless North 5th Street in Hunting Park.

According to the EPA, “urban heat islands" occur when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat.  This effect increases energy costs (e.g., for air conditioning), air pollution levels, and heat-related illness and mortality.  The urban heat island effect may be more severe in areas where tree canopy cover is low.  Researchers are beginning to unpack the ways in which tree canopy cover in neighborhoods is a reflection of a complex suite of factors.  Specifically, a long history of local, state, and federal policies have promoted residential segregation and preferential investment in certain neighborhoods in communities. Redlining was one such policy that was established by the federal government’s Home Owners’ Loan Corporation (HOLC) during the 1930s. For decades, redlining limited access to homeownership and wealth creation among racial minorities, contributing to a host of adverse social outcomes, including high unemployment, poverty, and residential vacancy, that persist today. While the multigenerational socioeconomic impacts of redlining and other similar local and state policies are increasingly understood, the USDA Forest Service is among the organizations leading the research to examine the environmental impacts and legacies of institutionalized discrimination.  Neighborhoods affected by such policies typically have substantially lower tree canopy cover than wealthier neighborhoods.  Policymakers can use this information to address persistent injustices that make some communities more vulnerable to extreme heat and other climate-related stressors.

Our Research

Urban trees provide many ecosystem services, such as mitigating the urban heat island effect and improving the quality of life in cities.  In the most vulnerable communities that may lack access to air conditioning, the cooling effect of trees may provide cooling  that can literally save lives.  However, neighborhood tree canopy cover is often a reflection of investment, advocacy, preference, or other factors that are more likely in neighborhoods with higher home ownership and wealth.  Redlined neighborhoods that faced divestment and disinterest from large swaths of society may have had a different trajectory, ecologically, than whiter and wealthier neighborhoods. 

As society examines and addresses issues of institutional racism, the lingering, dynamic, and ongoing effects of redlining’s impacts on urban environments and ecosystems are currently being examined by combining and analyzing multiple data sources, including Urban Tree Canopy Assessments (high-resolution tree canopy that includes LiDAR and parcel-level data), historic redlining maps, and/or high-resolution current ambient temperature data. 

One study examined how the HOLC policy administered 80 years ago may relate to present-day tree canopy at the neighborhood level. In our prior research in Baltimore, MD, Forest Service and other researchers discovered that redlining policy influenced the location and allocation of trees and parks. A subsequent analysis of 37 metropolitan areas shows that areas formerly graded D, which were mostly inhabited by racial and ethnic minorities, have on average ~23% tree canopy cover today. Areas formerly graded A, characterized by U.S.-born white populations living in newer housing stock, had nearly twice as much tree canopy (~43%). Results are consistent across small and large metropolitan regions. The ranking system used by Home Owners’ Loan Corporation to assess loan risk in the 1930s parallels the rank order of average percent tree canopy cover today.

Another study, from Philadelphia, PA, suggests long-term links between urban planning, disinvestment, and urban greening. Some redlined, predominantly black neighborhoods experienced depopulation, housing demolition, and redevelopment projects as part of broader urban renewal policies in post-industrial cities in the 1950s-60s. While these neighborhoods continue to have lower canopy cover compared to wealthier, whiter neighborhoods with lower housing density, there were actually substantial late 20th century increases in tree cover in neighborhoods that experienced urban renewal, like North Philadelphia. Such gains were due to a mix of plantings by non-profit programs and redevelopment authorities, as well as unintentional forest emergence on abandoned properties. The latter phenomena is an important mechanism of tree cover increase for cities located within forested biomes. There are complex connections across many decades between redlining, urban renewal, redevelopment, and urban greening initiatives.

Outcomes

While the data analysis and research have demonstrated the lingering effect that segregation has had on neighborhood tree canopy cover, there are also intervening factors such as urban renewal efforts and/or unintentional growth of “weedy” tree cover in abandoned lots.  It is important to note that there are complicated ways in which redlining, urban renewal, and other major urban land use and planning policies have and continue to impact tree cover.  A better understanding of these factors can inform strategies to remedy past injustices and prioritize tree planting to protect ecosystems and society, especially those that are most vulnerable to the effects of extreme heat and other climate-change related factors. With many US cities attempting to elevate environmental justice in urban greening and urban forestry, it is critical to better understand how our cities grew the tree cover patterns that exist today.

Research Results

Grove, Morgan; Ogden, Laura; Pickett, Steward; Boone, Chris; Buckley, Geoff; Locke, Dexter H.; Lord, Charlie; Hall, Billy. 2018. The Legacy Effect: Understanding How Segregation and Environmental Injustice Unfold over Time in Baltimore. Annals of the American Association of Geographers. 108(2): 524-537. https://doi.org/10.1080/24694452.2017.1365585.

Grove, J.M.; Cadenasso, M.; Pickett, S.; Machlis, G.; Burch, W. 2015. The Baltimore School of Urban Ecology. In The Baltimore School of Urban Ecology: Space, Scale, and Time for the Study of Cities. : Yale University Press.

Locke, Dexter H.; Hall, Billy; Grove, J. Morgan; Pickett, Steward T.A.; Ogden, Laura A.; Aoki, Carissa; Boone, Christopher G.; O'Neil-Dunne, Jarlath P.M. 2021. Residential housing segregation and urban tree canopy in 37 US Cities. npj Urban Sustainability. 1(1): 15. 9 p. https://doi.org/10.1038/s42949-021-00022-0.

Berland, A.; Locke, D.H.; Schwarz, K.; Herrmann, D. 2020. Beauty or Blight? Urban Greening in the Presence of Disinvestment. Frontiers in Ecology and Evolution – Urban Ecology. https://doi.org/10.3389/fevo.2020.566759

Pickett, S; Grove, M. An ecology of segregation. 2020. Front Ecol Environ. 18( 10): 535– 535, https://doi.org/10.1002/fee.2279

Roman, Lara A.; Catton, Indigo J.; Greenfield, Eric J.; Pearsall, Hamil; Eisenman, Theodore S.; Henning, Jason G. 2021. Linking Urban Tree Cover Change and Local History in a Post-Industrial City. Land. 10(4): 403. 30 p. https://doi.org/10.3390/land10040403.

Research Participants

Principal Investigators

  • Dexter Locke, USDA Forest Service Northern Research Station, Research Social Scientist
  • Morgan Grove, USDA Forest Service Northern Research Station, Research Forester
  • Lara Roman, USDA Forest Service Northern Research Station, Research Ecologist
  • Jarlath O'Neil-Dunne, USDA Forest Service Northern Research Station/University of Vermont, Spatial Analysis Lab Cartographer

Research Partners

  • Christopher Boone, Arizona State University - College of Global Futures, Dean
  • Laura Ogden, Dartmouth College - Department of Anthropology, Professor
  • Steward Pickett, Cary Institute, Plant Ecologist
  • Hamil Pearsall, Temple University - Geography and Urban Studies, Associate Professor
  • Theodore Eisenman, University of Massachusetts Amherst - College of Social & Behavioral Sciences, Assistant Professor of Landscape Architecture
  • Last modified: October 6, 2021