Let’s say you learn that your friend Beth is going to murder your other friend, Emily. You have two options: You can wait until Beth murders Emily, and then punish Beth. Or you can plant a tree and prevent the murder from taking place.
This thought experiment is of course fanciful. There’s no guarantee that a particular tree will stop a particular murder. But it does reflect reality on a broader scale—multiple studies have found a connection between the number of trees in a neighborhood and reduced levels of violence. Other urban features associated with reduced levels of violence include painted crosswalks, lighted walk/don’t walk signs, visible and available public transportation, and nearby public parks. So while the example of Beth and Emily may seem absurd, the tradeoffs made for models of individual punishment and deterrence at the expense of non-traditional, non-coercive crime prevention strategies are very, very real.
The relationship between trees and (the lack of) violence hasn’t received as much scholarly attention as it deserves, but the scientific literature that exists to date has been remarkably consistent. A 2015 comparison of tree canopy cover and “crime incident data” from the New Haven Police Department found that a neighborhood with 10 percent more tree canopy than another tended to have, after adjusting for other factors, 15 percent less “violent crime” and 14 percent less “property crime.” A similar study in Baltimore found that neighborhoods with 10 percent more tree canopy tended to have 12 percent less crime, and, notably, that the crime-stopping power of trees planted on public lands rather than private was increased by 40 percent. After an invasive species of beetle massacred ash trees in Cincinnati, a 2017 study found that areas where ash trees had been removed saw “significant” increases in crime. And the list goes on. Some studies compare apartment buildings within the same neighborhood, and some studies track tree cover and crime within specific neighborhoods over time, but all seem to support the proposition that more trees result in less crime. (“Crime” is not synonymous with violence and harm, but rather “things the state prosecutes.” However, crime is the most likely form of violence and harm to be tracked, and consequently the most likely to be used in tree canopy cover analysis.)
We don’t know why trees stop crime. The connection is not necessarily intuitive. Criminologists in the 1970s, 1980s, and 1990s actually insisted that vegetation encouraged crime by creating hiding places from which ne’er-do-wells might leap out and assault passersby (the “violent man hiding in the bushes” trope). Consequently, the conventional wisdom in urban planning was that in “high crime” (read: Black) neighborhoods, urban deforestation might actually be a positive.
Like most questionable legal ideas, the notion that trees cause crime can be traced back to England. In the delightfully titled “Trees Shed Bad Rap as Accessories to Crime,” environmental writer Richard Conniff reports that, some eight centuries ago, “King Edward I required English towns to clear the trees for 200 feet on either side of main roads as a precaution against highwaymen.” This anti-tree bias and its violent effects were resurrected in the 1970s through books with titles like Crime Prevention Through Environmental Design and Defensible Space, and reinforced throughout the 1980s and 1990s with a series of studies arguing that low, dense vegetation was associated with all manner of crimes.
The effects of this common “wisdom” can still be felt today. A study published earlier this year focused on redlining—the racially discriminatory housing policy established by the Home Owners’ Loan Corporation that was used to deny housing loans to people in majority-Black neighborhoods—and found that formerly redlined neighborhoods graded “A” (those set aside for “U.S. born white populations”) have twice as much tree canopy cover as neighborhoods graded “D” (where most residents were people of color.) This study is part of the growing science surrounding “tree inequality.” Poor, low-income, and historically Black neighborhoods are less likely to enjoy the many positive health benefits of trees, including their amazing ability to prevent violence and harm in our communities.
Does this sound ridiculous to you? It won’t if you’ve ever spent time in a city with a real summer. Not if you’ve taken one step outside of your home and felt heat hit you like a truck, like something solid. The kind of heat that makes trees want to pull up their roots and crawl under each other for shade.
Toni Morrison wrote: “You don’t know what heat is until you cross the border from Texas to Louisiana. You can’t come up with words that catch it. Trees give up. Turtles cook in their shells. Describe that if you know how.”
If you know what heat is, then I don’t have to tell you the difference between walking in direct sunlight on a black asphalt parking lot versus walking through a tunnel of enveloping green. If you know heat, you remember the difference on your skin. At some point, you’ve abandoned the shortest path to your destination in favor of the shaded path, and in that moment, you knew that trees were essential.
Once we crawl inside and pour ourselves a cool, refreshing beverage and sit for a minute, once our body temperature regains equilibrium, the misery of ten minutes before may seem a minor inconvenience. It seems ridiculous to say that it could be the cause of violence. But the entire structure of global capitalism orbits around ensuring convenience for people who can afford it. Countless nations have been ransacked so that other nations could season and sweeten their food, drink water from bottles, and enjoy bananas year-round. Our lives would look radically different without the thousand tiny conveniences shielding us from discomfort.
If you can bring yourself to remember what it’s like to be sweltering, dehydrated, and irritable, conjure that feeling now as I tell you that in the city of New Orleans, the temperature in some neighborhoods can be 18 degrees hotter than the official, recorded temperature. This is because of a phenomenon called “urban heat islands,” pockets of land that absorb and retain more heat than surrounding neighborhoods. In New Orleans, these heat islands are found in impoverished, largely Black neighborhoods like Hollygrove and Central City. There is a heat island covering the campus of Xavier University, a beloved historically Black school.
This is not merely inconvenient; it is dangerous. The U.S. Environmental Protection Agency reports both that heat waves claim more lives than any other type of weather event in the United States and that they are “expected to become longer, more frequent, and more intense” as climate change intensifies. In New Orleans, where summers are hot as hell but with more mosquitoes, it is not at all unusual for the recorded temperature to top 100 degrees on an August day—and, as I and other readers of the New Orleans Advocate recently learned, the machine that measures the recorded temperature for the city “sits in shade near heat-absorbing wetlands.” By the end of this century, according to an analysis by the Union of Concerned Scientists, Louisiana residents will have to endure three full months with a heat index of 105 or above.
Man-made climate change and also-man-made environmental racism will work in combination to ensure that the poor, Black neighborhoods of New Orleans are dangerously hot. People will die. It’s an example of what environmental humanities professor Rob Nixon terms “slow violence.” Slow violence, as defined by Nixon, is “a violence that occurs gradually and out of sight, a violence of delayed destruction that is dispersed across time and space, an attritional violence that is typically not viewed as violence at all.” For example, the accumulated effects of systemic racism result in shorter life expectancies for Black Americans, who can anticipate dying four years earlier than white Americans, on average. Slow violence is caused by structural injustice, rather than by one individual making a split-second decision. The absence of trees in formerly red-lined neighborhoods, and the consequent unbearable heat, is slow violence.
Even apart from the absolute certainty that people will die from the heat this summer and every summer after, and that the burden of that deadly heat will be borne unequally across racial and class lines, there are reasons to be concerned about heat island and shade inequality. The absence of mature, absorbent trees can lead to the flooding of streets and houses in low-lying areas. There is also a well-developed body of research showing that trees improve air quality by capturing pollutants, leading to lower prevalence of lung cancer and hospitalization for asthma, as well as reduced mortality overall.
Perhaps less known are the myriad ways that trees protect our minds. To quote the abstract of a 2001 study of residents in a Chicago public housing complex, “[c]onsiderable evidence suggests that exposure to ‘green’ environments can enhance human effectiveness and make life’s demands seem manageable.” The Chicago study sought to determine whether these effects were so great as to be noticeable in an urban public housing context where residents had very limited access to greenery. The results were striking: “Residents living in buildings without nearby trees and grass reported more procrastination in facing their major issues and assessed their issues as more severe, less soluble, and more longstanding than did their counterparts living in greener surroundings.” A companion study found, more relevantly for our purposes, that “[r]esidents living in relatively barren buildings reported more aggression and violence than did their counterparts in greener buildings. Moreover, levels of mental fatigue were higher in barren buildings, and aggression accompanied mental fatigue.”
City life is stressful and overstimulating. This is not just my opinion—it’s the conclusion of several studies indicating that mental health conditions are more prevalent among city dwellers, possibly due to “repeated exposure to strangers” causing “chronic engagement of the amygdala.” Whatever the cause, an emerging scientific narrative suggests that city dwellers are bearing a high mental load that reduces impulse control—and lack of impulse control can have deadly consequences.
Think about the moment you experience a surge of aggression. Think of the second before you lash out at a friend, when your mind hastily calculates whether maybe speaking in anger might have consequences down the line. It’s the moment in which you can decide not to act on impulse, a split second to reconsider that biting remark that would feel so good in the moment and so bad afterwards. If you are tired or hungry or dehydrated or uncomfortably hot, that opportunity to make a different decision becomes smaller and smaller, eventually dwindling down to nothing.
This moment of grace before you make a terrible decision occurs in the prefrontal cortex, the area of the brain that thinks ahead and calculates consequences. Recent research involving brain scans indicates that the frontal cortex, which is responsible for critical decision-making, is not fully developed until around age 25. From self-reported research, we know that “almost all adolescents” engage in criminalized behavior, and that rates of both official and self-reported delinquency “decline precipitously during the late teens and 20s” as the frontal cortex develops. All of us are most likely to participate in some form of criminalized behavior—from violence to drug use—between the ages of 15 and 19.
The science is so settled on this point that the U.S. Supreme Court, which is not known for being science-forward, has recognized teenagers as “less culpable” than adults in a series of opinions beginning in 2005, the year that the Court found it unconstitutional to execute children under the age of 18 (despite a sputtering dissent by Justice Antonin Scalia). The American Psychological Association has consistently filed amicus briefs in cases related to the punishment of children, reporting that “middle adolescence (roughly 14-17) should be a period of especially heightened vulnerability to risky behavior, because sensation-seeking is high and self-regulation is still immature.”
All of which is to say that for teenagers and young adults—for anyone below the age of 25—the moment of grace is already sharply reduced. This is before we factor in heat, or smog, or a lack of trees. Due to their brain structure, young people are biologically less capable of taking a moment to imagine the consequences of an irrevocable act.
Having been a teenager myself once, I don’t need scientists to convince me that teens are wired for bad decisions. I can easily bring to mind several moments where I made a decision that could have resulted in someone calling the police, and I know that their forbearance may have radically altered the course of my life. I know that the margin of error I have been afforded is a product of my race and class background. I know that my whiteness shielded me from regular interactions with police and the resulting violence: chokeholds, arrest, incarceration. But less visible than the consequences I’ve avoided when I made mistakes are the mistakes I’ve narrowly avoided making. How many times, on the verge of a poor decision, was I rescued by a cool gust of wind?
If I’d grown up in the same city, but in an urban heat island, would I have spent my summers sweltering and anxious? Could the airborne pollutants attacking my lungs also alter my mind and mood in near-imperceptible ways? Who would I have been in late August when the window unit broke, when my neighborhood was a tangle of frayed nerves, my community boiling and seething in the unrelenting and inescapable heat? In laboratory settings, people are more likely to display aggressive behavior when a room is uncomfortably warm. Studies using real-world heat and violence data show the same findings, in every region, across every span of time: where there is heat, there is violence. If urban heat islands don’t kill you with a heat wave, or with street flooding, or with air pollution that slowly destroys your lungs, they’ll kill you with violence.
For abolitionists, violence and harm are not the actions of sick individuals; they are symptoms of a sick community, blighted by oppression and need. And as recent epidemiological catastrophes demonstrate, when a community is sick, treating individuals who exhibit symptoms is not a sufficient response. To see results, we need to treat disease at the community level.
Angela Davis, former political prisoner and vocal abolitionist, wrote: “Prisons do not disappear social problems, they disappear human beings. Homelessness, unemployment, drug addiction, mental illness, and illiteracy are only a few of the problems that disappear from public view when the human beings contending with them are relegated to cages.”
As Davis indicates, abolitionists don’t see violence and harm as something you can root out by disappearing individual people. Over two million people are incarcerated in the United States, yet the social problems that are the root cause of violence continue to exist, and so the violence continues occurring. In fact, homicide rates in the United States are seven times higher than violence in other high-income nations that incarcerate far fewer people. If incarceration were an effective way to reduce violence, we would have seen results by now.
A public health approach to violence and harm emphasizes prevention. Our criminal legal system’s focus is the exact opposite: we invest mind-numbing amounts of time and money into isolating individuals, punishing them for acts of violence after those acts have already occurred through policing, prosecution, and incarceration.
We expend far less energy and effort combating the “slow violence” that often doubles as an underlying cause of criminalized violence. As the prominent abolitionist community organizer Mariame Kaba has observed, “crime” is not synonymous with violent or even harmful behavior: “All that is criminalized isn’t harmful, and all harm isn’t necessarily criminalized. For example, wage theft by employers isn’t generally criminalized, but it is definitely harmful.”
Our society’s approach to violence and harm deliberately ignores slow, systemic violence. It’s hard to know who to blame for air pollution, exactly—no one pulled the trigger. There is no individual to prosecute, penalize, or incarcerate. Yet the person who dies of lung cancer or a severe asthma attack is exactly as dead as the person who was shot.
The most catastrophic example of slow violence, of course, is climate change. According to the World Health Organization, climate change already causes over 150,000 deaths annually. When structural violence is the killer, no one is prosecuted. And no amount of prosecuting individual people will bring us any closer to ending, or even mitigating, climate change. We can throw all of the money in the world at police departments, and the death toll will continue to rise. The carceral state has no response to slow violence.
But we have protectors. While they are not a panacea, trees are multidisciplinary specialists in preventing slow violence. Trees cool and soothe. Trees drink carbon dioxide and floodwater. And in the instant that someone is about to make the worst decision they have ever made, irrevocably altering the lives of everyone around them, trees offer an extra fraction of a second, a moment of grace and the potential for something better.
In addition to cooling the street and removing airborne pollutants, some scientists have hypothesized that trees trigger the neighborhood’s natural immune response to violence—what urbanist Jane Jacobs called “eyes on the street.”
Jacobs, a grassroots organizer and author who transformed the field of urban planning with her vocal opposition to “urban renewal” and “slum removal,” wrote that “[a] city street equipped to handle strangers, and to make a safety asset, in itself, out of the presence of strangers, as the streets of successful city neighborhoods always do, must have … eyes upon the street, eyes belonging to those we might call the natural proprietors of the street.” In order to do this effectively, Jacobs wrote, “the sidewalk must have users on it fairly continuously, both to add to the number of effective eyes on the street and to induce the people in buildings along the street to watch the sidewalks in sufficient numbers.”
We should distinguish this from more sinister models of surveillance, such as the proliferation of police cameras: Jacobs stresses the need for “a clear demarcation between … public … and private space.” It’s a kind of surveillance that only extends to our public life, which would mostly be taking place on the street anyway. Also, this surveillance isn’t the domain of prison officials, law enforcement, or some external authority—Jacobs is talking about communities watching each other, knowing each other, and holding each other accountable through a shared public life.
As Kuo and Sullivan, two scientists who changed the scientific conversation about trees and crime, speculated in 2001: “There is some evidence to suggest that in inner-city neighborhoods, vegetation might introduce more eyes on the street by increasing residents’ use of neighborhood outdoor spaces. A series of studies conducted in inner-city neighborhoods has shown that treed outdoor spaces are consistently more well used by youth, adults, and mixed-age groups than are treeless spaces; moreover, the more trees in a space, the greater the number of simultaneous users … Not surprisingly then, a recent study found that children were twice as likely to have adult supervision in green inner-city neighborhood spaces than in similar but barren spaces.”
Abolitionists have long said that a safe community is a community where members know, care for, and watch out for each other. Mariame Kaba’s June 2020 op-ed for The New York Times laid out a vision for a safer abolitionist society:
“When people, especially white people, consider a world without the police, they envision a society as violent as our current one, merely without law enforcement—and they shudder. As a society, we have been so indoctrinated with the idea that we solve problems by policing and caging people that many cannot imagine anything other than prisons and police as solutions to violence and harm.”
People like me who want to abolish prisons and police, however, have a vision of a different society, built on cooperation instead of individualism, on mutual aid instead of self-preservation. What would the country look like if it had billions of extra dollars to spend on housing, food, and education for all? This change in society wouldn’t happen immediately, but the protests show that many people are ready to embrace a different vision of safety and justice.
Trees are but one component of creating safe, accessible, sustainable, nurturing communities that acknowledge the slow violence of economic exploitation and environmental racism and that minimize its impact. They are a familiar, tangible example of how small changes to urban environments can result in safer communities.
At the end of Freedom Dreams, a book included in the open-source abolitionist curriculum “Study and Struggle,” Robin D.G. Kelley envisions abolition as a park: a tangible, public space where our collective needs and desires can be met. Kelley suggests that this “Freedom Space” be built on the site of the ruins of the World Trade Center (Freedom Dreams was published in 2002) and that it be funded with a percentage of each nation’s military budget. He writes: “This would not be just any park. Imagine a space filled with odd, beautiful play structures intended to force people to engage each other.” (Jungle gyms, he explains, were “originally designed in post-Nazi Germany as a way to enable free, unstructured, democratic play.”) He continues: “I can envision a section composed of large round picnic tables, a great lawn for playing and dreaming, sandboxes for kids of all ages, works of art that we can engage organically rather than as distant object … works of art that might spur us to talk to each other.” This is a space designed for us to interact in, to see and be seen by each other. And of course, “[a]ll performances are free. Indeed, everything should be free, including food and drink. And how about a row of nice, airy bungalows with beds and showers for the homeless?”
This is infrastructure as it should function—not in the service of capital, but in the service of community, working to maximize our bonds with and accountability to each other. The Freedom Space would be an accessible hub for mutual aid projects, community organizations, and study groups to gather. With a Freedom Space in every neighborhood, frequent visitors to the park might come to know each other, creating the strong communal bonds that keep us safe.
We can create Freedom Space. Liberation and joy are possible. But first we must be able to imagine ourselves outside of the confines of artificial scarcity. We must be able to imagine ourselves as part of a community that will care for us, even and especially during challenging times.
When I imagine myself in Freedom Space, there are no cops and no fences. Instead, there are people around me—people who care about me, who will intervene if they believe that I might be harmed. Instead of scarcity, there is abundance. And above my head, a lush canopy of trees.♦
Amelie Daigle serves as Editor-in-Chief of the NYU Review of Law & Social Change, the progressive law journal that all the cool kids are reading. She would like to thank Helen Campbell for providing comments on this article before anyone else was allowed to see it, and Lyta Gold and Cate Root for their editorial insight and labor to bring this piece to fruition. Find her at her urban tree canopy stan account, @AnomalousAmelie on Twitter.
This article originally appeared in print in the July/August 2021 issue of Current Affairs. It is republished here with permission.