Mitigating Climate Change in Cities Requires More Than Planting Trees
Numerous scholars (1, 2, 3, 4) and commentators (5, 6, 7, 8) have lamented the loss of green cover and its inequitable distribution in many of America’s cities. The loss of trees is particularly significant considering their potential to mitigate the rising temperatures that accompany climate change and the excessive air and noise pollution that plague our cities. But simply planting trees to address the human toll from these problems -- which is most severe in low-income neighborhoods -- is not the solution.
Many of the wealthiest neighborhoods have a vibrant urban forest, whereas poor neighborhoods are much more likely to have busy roads, impervious surfaces and a paucity of parks and green cover. The absence of tree canopies, in particular, exacerbates the heat, noise and negative air quality effects experienced by those living and working in our nation’s most impoverished neighborhoods.
In some instances, these inequalities date back nearly a century to the redlining and other predatory practices that moved investment away from neighborhoods dominated by the poor and people of color. Several recent articles (9, 10) have used high-altitude airborne and satellite imagery to document the systemic lack of investment in urban greening over time in such neighborhoods.
Our work on the USC Urban Trees Initiative, which now includes multiple communities in South-Central and East Los Angeles, connects faculty and student researchers with local government and non-profits via the USC Dornsife Public Exchange. This interdisciplinary initiative uses various forms of mapping, air quality analysis, and landscape schematics to optimize where to plant trees, in what configuration, and which species to plant to mitigate air pollution and extreme heat. The initial work focused on the El Sereno, Lincoln Heights and Ramona Gardens communities in East Los Angeles and found more residents than trees and more trees on private than on public property.
We also proposed numerous scenarios to begin the task of greening these neighborhoods. However, one fear is that the greening of low-income neighborhoods may initiate their gentrification, forcing residents to move to other parts of the city with similar or worse conditions than they currently experience.
To minimize that risk, tree planting efforts need to reflect the needs and aspirations of the current community residents. Some may be homeowners and others may be renters, but all need to play an active role in the establishment of goals and the development and execution of the plans to accomplish those goals. We have developed a series of landscape schematics to show what is possible, and we are working now to use these designs to engage residents using community meetings and walking tours as a precursor to soliciting their help in preparing and executing tree planting plans.
The tree planting should span private property as well as public right-of-ways, parks and school campuses. The local residents -- those of working age as well as the children and the elderly -- need to be engaged from the start to ensure that the forest they create generates a sense of belonging and community pride. These bonds will be strengthened if parallel efforts are made to support workforce development so that local residents can be recruited and employed by city departments, non-profits, and other stakeholders with an interest in helping to plant and sustain this urban forest.
The relentless march of climate change also suggests an active role for science, because the trees we plant today will need to prosper in a much warmer world in 30-40 years when they reach maturity. We anticipate that the number of days with temperatures exceeding 95 degrees Fahrenheit in places like El Sereno and Lincoln Heights will quadruple from 15 to 60 days by 2060. The choice of trees we plant today needs to anticipate the warming climate and the paucity of water in Mediterranean climates like we find in Southern California. We can also choose to plant trees with a goal to optimize other outcomes. For example, some residents may wish to plant fruit trees on private lots or in and around community gardens, as a way to supplement their food supply and improve diets. Others may want to plant trees in specific locations and configurations to help reduce noise and air pollution near freeways and local streets. This is a topic where we need more study because it is not clear which tree species take particulate matter from the atmosphere and how the configurations (i.e., single vs. multiple trees) used to plant trees influence such outcomes. Similarly, some tree species should be avoided altogether given their propensity to exacerbate some residents’ allergies.
The story painted here calls for an all-hands-on-deck approach that enlists scientists, landscape architects, and local community residents as co-developers of more sustainable and resilient neighborhoods. The solution to address the human toll from air pollution and extreme heat -- particularly their disproportionate effects on low-income neighborhoods -- is more complex than simply planting trees.
About the Author:
Dr. John P. Wilson is a Professor of Architecture, Civil and Environmental Engineering, Computer Science, Population and Public Health Sciences and Sociology at the University of Southern California where he also directs the Spatial Sciences Institute and Wilson Map Lab. His research focuses on the modeling of coupled human-environment systems and makes extensive use of GIS, spatial analysis and various forms of environmental modeling. Most of his work is collaborative with the goal of improving our understanding of the factors connecting people, the environment, and human well-being.