Rooted in Research: Greening Cities for Health, Safety, and Well-Being

Could cleaning and greening vacant lots not only improve the look of neighborhoods, but have positive impacts on health, safety, and well-being? University of Pennsylvania researchers have been addressing this question, and they shared their most recent findings at a January 2023 online event co-hosted by Penn IUR, Analytics at Wharton, and Pennsylvania Horticultural Society (PHS).

With an introduction by Vice Dean of Analytics at Wharton, Eric Bradlow, and moderated by Penn IUR Co-Director, Susan Wachter, the conversation centered on the social and economic value of greening vacant lots. A panel of Penn researchers presented their work, including John MacDonald, professor of criminology and sociology, School of Arts and Sciences; Shane Jenson, professor of statistics and data science, Wharton; and Michelle Kondo, research social scientist with the USDA-Forest Service who completed her postdoctoral training in environmental health and epidemiology at Penn.  

PHS’s President Matt Rader opened the program with an overview of PHS’s LandCare program, which greens and cleans 13,000 vacant lots throughout Philadelphia, turning eyesores into community assets. PHS uses horticulture to positively impact healthy outcomes via social determinants of health, such as healthy food access, economic opportunity, livable environments, and social connections. Rader said he believes that a well-gardened public realm is not a nice-to-have amenity but a “must-have element of a healthy neighborhood.” Greening can also “affordably and equitably advance health and well-being.”

While new research bolsters the connection between greening, safety, well-being, and economic vitality, the collaboration of Penn researchers with PHS is longstanding. In 2006, Penn IUR and PHS co-hosted a conference, Growing Greener Cities, which resulted in a book of the same name, edited by Penn IUR’s co-directors, Susan Wachter and Eugenie Birch. In one of the chapters, “Green Investment Strategies and Urban Neighborhoods,” Wachter, Kevin C. Gillen, and Carolyn R. Brown showed that commercial greening, vacant lot management, and neighborhood greening all conferred additional value to homes and the desirability of neighborhoods, especially when deployed by business improvement districts.  While the conference explored green interventions in cities around the world, the connection between Penn IUR and PHS would continue as both organizations share a home base in Philadelphia.

Penn IUR faculty fellows have been at the forefront of showing how green infrastructure can contribute to a city, often using PHS’s data about greening initiatives around Philadelphia. For example, in their 2018 paper, “Effect of Greening Vacant Land on Mental Health of Community-Dwelling Adults,” researchers Eugenia South, Bernadette Hol, Michelle Kondo, John MacDonald, and Charles Branas showed that residents living with a quarter mile of revitalized lots had a 41.5 percent decrease in feelings of depression compared to those who lived near lots that had not been cleaned.

At January’s Rooted in Research event, John MacDonald noted that “the idea that there are benefits to vacant lot remediation is consistent with theories in criminology,” such as the “broken windows” theory that a lack of neighborhood maintenance can encourage criminal activity. MacDonald showed that in Philadelphia, the greening of 12,788 vacant lots between 2006-2018 resulted in a 5.59 percent overall drop in crime, with a 20 percent drop in robbery. MacDonald noted that in Philadelphia, 3 percent of streets contribute to 50 percent of shootings; in these locations, greening and cleaning vacant lots could have a major impact on violence in the city.

Michelle Kondo shared a meta-analysis of eight studies of vacant lot remediation. She explained that there is nuance to the kind of greening that is effective. For example, one study showed that mowing vacant lots did not significantly reduce firearm violence, but greening and gardening did by more than 5 percent. Kondo also shared her research co-authored with Eugenia South, Charles C. Branas, Therese Richmond, and Douglas Wiebe, which showed that tree cover could provide protection against gun violence, as tree cover was inversely associated with gunshot assault.

Finally, Shane Jensen presented research that he and Susan Wachter conducted using property sale data and sophisticated housing models, showing that PHS’s LandCare program can provide a benefit of $200,000 in real estate value to properties neighboring improved vacant lots far exceeding the several thousand dollar estimated cost. In a forthcoming paper to be published in Real Estate Economics, the team compares 4,651 lots that had been greened from 2007-2017 against a control group of 16,799 untreated lots from that same period. On average, properties within a 1,000-foot radius of a greened lot experience a 4.3 percent increase in value after the first year and a 13 percent cumulative increase after six years. Compared with the relatively small cost of greening, the LandCare treatment provides a substantial return on investment.

As the panelists took questions from the audience, Wachter asked about concerns that greening vacant lots can lead to gentrification. Jensen acknowledged that while the benefit of increased property values is focused on homeowners, the entire community reaps the safety and mental health benefits of an improved physical realm. MacDonald added that there wasn’t any evidence of greening causing gentrification in his studies. By contrast, the demographics of the neighborhood do not seem to change after the greening is done.

When asked why research matters, Rader said that there are still thousands of vacant lots that have yet to be greened. “Research helps us tell the story to residents and policymakers and other civic leaders,” he said, and helps reinforce the need to improve those untended vacant lots.

To learn more, watch this video on the research by Wachter and Jensen.