In low-income Phoenix neighborhoods, the lack of shade trees is a question of equity
In central Phoenix, rows of multidecadal Aleppo pines and evergreens form lush corridors along residential city streets. Their canopies expand over roadways and sidewalks, diverting the Phoenix sun, allowing for a thriving ecosystem of human activity to form within its cover. Couples walk on sidewalks pushing strollers, a teenager rides his bike in the designated lane and an elderly man tends to a flowering rose bush in his front yard.
About seven miles away, a South Phoenix neighborhood built alongside a freeway bakes in the sun, its asphalt exposed from sunrise to sunset with limited tree cover across the residential area.
People find their way under the shade of the sparse tree population. In an adolescent rite of passage, three children climb and hang upside down from the limbs of one of few trees. Down the street, a man takes a phone call in his backyard as he leans his weight on a branch of a tree that is just a few feet taller than him. And construction workers tuck away in the shade, chugging root beer as they hide from the sun.
Some contrasting characteristics of the two neighborhoods are more apparent in terms of the green dome of leaves and their shade, but a bigger discrepancy is the root of their differences: income and race. And lack of shade can have serious effects for community health and resiliency in adapting to hotter and longer summers.
That’s, in part, why Phoenix is looking to revise its 13-year-old tree and shade master plan. The original and current goal of the plan is to reach 25% canopy cover across the entire city by 2030 to reduce heat stress and minimize negative effects to human health and activity.
But a blanket goal of 25% may not address the critical issue of where the shade is needed most. Some areas are more in need of trees than others, which means focusing on individual neighborhoods or even streets.
“The goal needs to be more nuanced,” said Lora Martens, the urban tree program manager for the city’s office of heat response and mitigation “Certain areas need more tree coverage, so I’m not sure a blanket 25 percent is the right goal to have.”
But the city still faces an array of hurdles to get more people in the shade. Phoenix’s messy urban design, heat islands and private land all stand in the way of reaching tree equity.
Urban areas are particularly vulnerable to climate change due to extensive concrete and asphalt, increased pollution, greater population densities and a concentration of infrastructure that intensifies effects from urban heat, drought and extreme weather. Urban forests and tree cover provide a critical role in helping cities address climate change by supporting greenhouse gas mitigation and reducing the effects of extreme heat and altered climate that impair human health.
Lowest tree canopy rates are in south Phoenix
Minimizing heat stress is a top priority for the hottest major U.S. city. Last year, heat killed at least 359 people across Maricopa County. Extreme heat is also linked to an increased risk of heart disease and stroke, among other health complications.
The city uses studies conducted by Arizona State University on tree equity, geographic system modeling, and the American Forests tree equity map to determine which areas officials believe need more trees.
The tree equity map calculates a score based on how tree canopy and surface temperature align with income, employment, race and health factors, and is broken down by census block groups.
“There’s a strong correlation between canopy cover and demographic,” said Ariane Midel a professor and researcher at Arizona State University “Neighborhoods that are lower income or Hispanic neighborhoods traditionally have less canopy cover to begin with, but they are also more vulnerable because they have less resources.”
The worst-scoring neighborhoods in Phoenix are mostly in the southern part of the city and near Sky Harbor International Airport.
The neighborhood with the lowest tree equity score in the city — where the children climbed trees — is bound by Buckeye Road to the north, 19th Avenue to the east, and Interstate 17 to the south and west. Most of the homes here are affordable housing units.
This region, which also houses an elementary school and a public park, has less than 1% of canopy cover. People of color make up 97 percent of the population and more than 90% of the people who live in the neighborhood live below the poverty threshold, with a median household income of $11,016.
Uptown, In the lush neighborhoods sprawling from either side of Central Avenue between Missouri and Dunlap avenues, canopy goals have been “achieved” with roughly 20% cover throughout the area. A cluster of neighborhoods in the area ranks the best in the city for canopy cover. In one census block, people of color make up only 3% of the population. The median household income there is $187,344.
The south Phoenix neighborhood scores a 32 out of 100 on its “equity score.” The uptown neighborhoods are the highest scoring in the city with a perfect 100.
Areas in the city with less tree cover tend to have higher concentrations of Hispanic populations, according to census data. Hispanic households make up more than 90 percent of the population in the lowest-scoring neighborhoods.
Urban heat island increases need for shade
Urban areas across the world are seeing rising temperatures, in part as a result to the urban heat island effect, which is caused by buildings and streets absorbing heat throughout the day and re-emitting it at night.
Phoenix’s urban design and sprawl maximize the dangerous effects of the heat island in an already sweltering city.
“The way Phoenix was designed is conducive to this urban heat island,” said Midel. “In order to get around we need cars because everything is so far away and in order to do that we need roads and parking lots.”
Phoenix is a sprawling city built on a grid street plan, and public transportation cannot serve every area equally, making commuting by car the most popular way to get around. Because of this, many city streets are wide, stretching across seven or more lanes. And to account for all these cars, Phoenix has a lot of parking spots. A 2017 study suggests that metro Phoenix had more than 12 million parking spots, making up about 10 percent of the entire region’s land use.
All of this asphalt absorbs heat and spits it back out in the nighttime, making the city hotter than surrounding rural areas. Midel says there are not enough trees to make up for all that extra heat found in the city’s urban core.
“Our roads are so wide, and the buildings are usually single-family homes and are set back with a front yard so there’s no way to create shade with buildings as well,” said Midel. “It’s much more uncomfortable during the day because there is a lack of shade, and the urban form definitely contributes to that.”
Midel says the car-centric city design is one reason why expanding urban forestry in Phoenix so important: Trees and vegetation lower both surface and air temperatures by providing shade and through evapotranspiration. Shaded surfaces may be 20–45 degrees Fahrenheit cooler than the peak temperatures of unshaded materials, according to the EPA.
“It’s really important to think about where to place those trees because city resources are limited,” she said “It’s really important to pick the locations where they have the biggest impact, and that’s where people actually are; where they walk, where people wait for the bus, maybe in parks. These areas where tree shade can have a direct impact on people.”
The city does not have a publicly accessible tree inventory, but Martens says they are working to plant trees in areas where people are moving around outside. The city’s Park and Recreation Department is working toward planting 1,500 new trees a year in parks.
In 2020 the city’s street transportation department implemented its cool corridors program. The $1.5 million project aims to plant 200 trees per mile for a total of 1,800 new trees planted across nine projects.
Martens says the transportation department is working to plant trees on the busiest and biggest streets in the city to reduce the effects of heat stress on pedestrians or people who rely on public transportation.
Planting trees adds expense, work for homeowners
In addition to greening a concrete jungle, getting more trees on private land is a hurdle the city has struggled to deal with. The city only has the authority to plant trees on municipal property and public rights of way, along city streets or public parks. This limits the resources available to reach their current goal of 25% canopy cover.
The city is hoping to start a grant program this summer, with implementation in the fall, to get more trees planted in neighborhoods to rapidly expand canopy cover.
“The city doesn’t own enough land to plant that many trees,” said Midel. “So you need people like you and me to chip in and plant some trees in our front yards and back yards. But lower-income families will probably not have the resources to purchase, maintain and water those trees.”
Adding trees can be a financial burden for a homeowner, especially for low-income families in neighborhoods where trees are needed most. Adding trees to a property would likely create a higher water bill and maintenance would be required to keep the tree alive and healthy.
“Trees are kind of like a pet, you can’t just get one and that’s it,” said Aimee Esposito, executive director of Trees Matter, a nonprofit based in Phoenix that aims to educate and promote increased tree canopy across the Valley. “When we go into a community that already has limited resources in time, energy, and financials we also need to show with resources to support them.”
Shade from trees may offset the cost of a higher water bill by reducing the need for air conditioning. A study that looked at homes in California found planting trees on the west and south sides of a home can reduce a household’s summer electric bill by about $25 a year.
“It’s kind of a double whammy, right? So people who don’t have enough money to run their air conditioning, they’re also then living in these neighborhoods that have less shade or less resources,” said Midel. “There are all these aspects that go into this vulnerability while there all of these things that happen at the same time that increase their vulnerability.”
The city says it is working with water services department to identify how much of an increase in water bills a new tree would represent.
“We are trying to get some real numbers to be very transparent about the cost of a tree for a private homeowner,” said Martens. “We are very concerned with asking people to take on a responsibility they don’t understand.”
‘It’s a matter of public health’
Trees Matter has its own prioritization map that differs from the city’s, one that looks at heat-related deaths and illness, income demographics and cardiovascular disease rates to determine areas that would benefit the most from expanded tree canopy. The group has mostly planted on school campuses but is in the beginning stages of doing neighborhood plantings.
Esposito says starting with schools can promote increased canopy cover in a neighborhood and get communities excited about adding more trees.
They group planted 33 trees at Mary Mcleod Bethune School in south Phoenix last month, in the heart of an area that severely lacks tree cover. The school already had an irrigation system in place, which allowed for this planting to be executed.
The school is a majority-minority, with 76 percent of the students at the school identifying as Hispanic.
They planted trees like desert willows and red push pistache inside the school’s campus to add vibrant colors for students on their walk to class, in hopes of improving mental health and atheistic value. Outside along the baseball fields and near bus stops, the group planted trees that will grow larger, like acacias, which will provide year-round shade for students.
Trees Matter and other groups recently worked with state Sen. Mitzi Epstein, D-Tempe, to introduce the “trees for kids bill,” an attempt to get more trees on school grounds. The state budget that passed in May includes $300,000 for planting trees at low-income schools across the state. The group calls it a major win for equity for children and communities across Arizona.
And while more shade is now found at Bethune, a lack of critical canopy cover still plagues the areas surrounding the school ahead of Arizona’s hottest months.
Across the street from the campus, a group of people wait for the Valley Metro bus. They wear big hats to block to the sun, and one man lifts his white t-shirt from the hem and dabs his forehead. The sun beats down on this part of town, with temperatures nearing 100 degrees in May as the asphalt and pavement absorbs the heat that it will release back into the atmosphere at night, fueling the urban heat island.
“These people need trees,” said Midel about the neighbors of south Phoenix. “It’s a matter of public health, it is so important.”