America has a tree problem. It may not be obvious, but as it turns out, trees are unevenly distributed, a situation known as tree inequity. Urban areas have fewer trees, while suburban areas have more trees. Although these different environments lend themselves to varying amounts of tree cover, the lack of trees in urban centers is harming people in many ways.
The Roots of Urban Heat Islands
Heat islands are areas where the temperature consistently exceeds that of the surrounding areas. This is generally due to an abundance of impervious surfaces, like concrete, brick and asphalt, that absorb heat and then radiate it back after dark. It seems obvious that no one would want this, especially in the summer, but there are deep historical and structural reasons that heat islands persist today.
“The main reason that tree cover is so unequal in the U.S. has to do with where we live,” says Robert McDonald, lead scientist for nature-based solutions at The Nature Conservancy. “Low-income neighborhoods have about 15% less tree cover on average than high-income neighborhoods and are about three degrees Fahrenheit hotter on average. Ninety-two percent of US communities have this pattern where high income neighborhoods have more tree cover than low income neighborhoods.” This is often due to neighborhood design and population density, McDonald explains.
“Most low-income households and most households of color live in the urban center, and more wealthy households have tended to move out to suburban settings. When you're in a suburban setting, you have a lawn, it might have some tree cover, and you're just settled less densely, whereas when you're in a city center, you're often in apartment buildings. There's more pavement nearby, so there's less green and there's more heat, because there's more pavement that's absorbing the energy from the sun.” Urban versus suburban areas are a structural reason for heat islands to exist, but researchers have been curious about the actual roots of these heat islands and have been comparing them to maps of traditionally redlined neighborhoods. Stephen Fong, a professor of chemical and life science engineering at Virginia Commonwealth University in Richmond, Virginia, and his team, for example, went street by street in Richmond, mapping heat islands that they later compared to historical maps. “You can see which areas were redlined and which weren't historically,” says Fong. “To me, one of the most eye-opening things was that you see that these policies that are 100 years old still have an impact today.”
What’s the Problem With Tree Inequity?
Although it can be argued that real estate prices are influenced by the presence or absence of tree cover and green space, larger functional issues are at play when it comes to tree inequity. Trees cure, or contribute to improving, several issues facing modern humans simultaneously.
“Trees cool primarily by shading impervious surfaces so they're preventing that pavement from absorbing the sun,” says McDonald. “They also cool because they transpire water. So just like on a hot day when you sweat, and the sweat evaporates off you, making you feel cooler, trees transpire water. That's about equally as important for cooling. There's also interesting work on how trees regulate air quality, they can help reduce particulate matter.”
However, it’s not just air quality or the heat island effect that trees can improve – they have actually been shown to enhance both physical and mental health, contributing to a sense of well-being for people. “When you ask people to think about some place that's peaceful and calm and quieting, that they can just center themselves and be away from the bustle of life, most of the time, people think of something that is quiet in nature,” says Michael Austin, senior associate with urban design firm Cooper Robertson in New York City. “A lot of people would think about a forest or a tree. It's just actually a mental relief, too, to be surrounded by trees.”
Solving the Problem of Tree Inequity
If trees are so beneficial to humans, shouldn’t it be as simple as having every person plant a few to improve the quality of life for everyone? Someone has to pay for the trees and commit to their upkeep, which requires major long-term investment. Unfortunately, simply planting trees doesn’t address some of the larger structural and socioeconomic problems that go hand-in-hand with urban heat islands.
“Even if there's an investment in an area that's typically been depressed or economically impoverished – you hear about the gentrification of certain neighborhoods – then it can actually push out the people that were living there because they can't afford to live there any longer,” says Fong. “Even for those that are well-intentioned, there are secondary unintended consequences.”
How does a municipality approach tree inequity without displacing residents who should benefit? Getting affected neighborhoods involved is a first step. “When it comes to residential communities, the first thing I would always ask is ‘Has anyone talked to the community?’” says Austin. “It’s important to ask questions like: ‘What does the community want? What are their goals and what are their concerns?’ Is it a concern that if we start to do a tree planting strategy that may improve the quality of life, will it increase the risk of displacement? Does it lead to increasing affordability, or increasing land value and decreasing affordability?
