A lack of tree cover in parts of many cities contributes to the urban heat island effect, exacerbating the effects of climate change. (City and County of Denver)
How much of the open space, sidewalks and other land in your neighborhood is shaded by trees? It depends on where you live — and, environmental advocates say, on decades of inequities that break down along class and racial lines.
Only about 3% of Sun Valley, a west Denver neighborhood where 94% of residents live in poverty, is covered by tree canopy. Just a few miles away, West Highland has a tree canopy cover of 18%, with only 12% of residents living in poverty.
Why do these disparities occur? American Forests, a conservation nonprofit, recently launched a measurement called tree equity scores for thousands of neighborhoods in the United States. A tree equity score is based on the employment rate, age, health, income, race, population density, surface temperature, and existing tree canopy of a neighborhood. If a neighborhood has a score of 100, it has achieved tree equity.
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The tree equity score also includes the priority index, which was developed to “help prioritize the need for planting to achieve tree equity,” according to its website. The priority index includes the unemployment rate, the percentage of people who are white and non-Hispanic, the ratio of seniors and children to working-age adults, and the percentage of population below 200% of poverty.
American Forests says it created tree equity scores to be a resource for environmental advocates to “help make the case for more investment in neighborhoods with the greatest need for trees, jobs and protection from the effects of climate change.”
Tree cover can reduce temperatures and combat the urban heat island effect, which disproportionately affects low-income people and people of color. Research cited by the National Wildlife Federation states that trees in parking lots have been shown to reduce asphalt temperatures by 36 degrees Fahrenheit.
Generally, the tree equity scores show that the wealthier an area is, the more tree canopy it has, and the lower its temperatures.
“The reason why we created tree equity scores is because historically and nationally in many cities, trees have not been equitable,” Chris David, vice president of GIS and data science for American Forests, said in an interview.
How Colorado neighborhoods fare
The American Forests report highlights deep disparities in tree cover among communities along the Front Range.
Irondale, a neighborhood in Commerce City, has a tree equity score of just 25; about 84% of its residents are people of color, and 67% of residents live in poverty. Meanwhile, the area surrounding Country Vista Park in Broomfield, which comprises 12% people of color and has only 8% of residents living in poverty, has a tree equity score of 95. Despite this significant difference in tree equity scores, Country Vista Park is only about 17 miles from Irondale.
A section of Castlewood, a neighborhood in Centennial, earned a tree equity score of 100. Ten percent of residents in that section are people of color, and only 7% of residents live in poverty. Other high-ranking communities include Manitou Springs, a popular tourist location near Colorado Springs, along with affluent Denver suburbs Greenwood Village and Cherry Hills Village which both have a tree equity score of 100.
Denver’s urban forest covers 19% of the city and provides “$122 million in benefits to residents each year,” according to the Office of the Denver City Forester website. A Denver Parks and Recreation dashboard allows individuals to access “Treeport Cards” for neighborhoods in Denver, and see data regarding the number of trees in a neighborhood, the types of trees in a neighborhood, and the approximate ecosystem benefit savings.
According to the dashboard, Sun Valley has 412 trees and an annual ecosystem benefit savings of $29,910. Located approximately three miles away, West Highland has 4,768 trees and an annual ecosystem benefit of $533,590.
Northern Commerce City has a tree cover of just 3%, peak temperatures of 95 degrees Fahrenheit, and an overall tree equity score of 40, according to American Forests’ report. (The report analyzed average surface temperatures on the three hottest, clearest days within the last four years, David said.) Most of Boulder has a score of 100. La Salle, a statutory town in Weld County, has a tree equity score of just 43. Almost 50% of residents in La Salle live in poverty.
Such a low level of tree cover, such as in Commerce City, can lead to an exacerbation of existing health conditions, whether it’s asthma or other respiratory diseases, or heart disease, according to David. “It’s dangerous,” he added. A low tree canopy can also reduce air quality.
The tree equity score website states that its canopy goal for northern Commerce City is 24%. In many neighborhoods in Colorado, American Forests’ tree canopy goal is 24%. Some neighborhoods have a different goal because American Forests adjusts the goal based on population density, according to David.
When asked how long it might take for Commerce City reaching the 24% tree canopy goal, David said they cannot really put a time frame on it because it depends on several different factors, such as the level of investment each neighborhood has. “What we can say is we think every neighborhood should achieve tree equity and have a score of 100,” David said.
The tree equity score allows people to set their own targets, so one suggestion David had for increasing tree equity in areas is for city planners — whether that’s the urban forestry division, the mayor’s office, or the urban planning division — to set initial targets to get all neighborhoods up to a certain score, and then increase the target from there. If city planners can determine which neighborhoods have the lowest tree equity scores, they can focus on getting those neighborhoods up to the initial target threshold, and from there, city planners can adjust their targets to getting every neighborhood up to a higher tree equity score.
“You can set those interim targets so it doesn’t feel like a completely overwhelming or unmanageable goal to achieve,” David said.
What’s being done in local communities
Cities and local communities across Colorado are working to preserve and maintain tree canopy.
In 2019, Colorado Springs conducted an Urban Tree Canopy Assessment, in which PlanIT Geo, an urban forestry consulting firm, analyzed aerial images of tree canopy in Colorado Springs from the 1990s and in 2015 and 2016 to compare how the tree canopy has changed. According to the assessment, Colorado Springs had 17% urban tree canopy in 2015, up from 14% in 1999. Of the 83% of Colorado Springs that was not covered by tree canopy in 2015, 29% was deemed suitable for future tree planting.
As part of the assessment, the Colorado Springs City Forestry division released the proportion of Colorado Springs tree canopy that each ZIP code had as of 2015. The areas with the lowest proportion of Colorado Springs’ tree canopy were southeastern Colorado Springs and the area surrounding Peyton, a rural unincorporated town. The affluent neighborhood of Broadmoor in southwestern Colorado Springs had one of the highest percentages of tree canopy.
Since 1977, the report noted, Colorado Springs has been certified under the Arbor Day Foundation’s Tree City USA program. To qualify for Tree City USA certification, cities must meet four standards: having a tree department or board, having a community tree ordinance, spending at least $2 per capita on urban forestry and celebrating Arbor Day. Many cities in Colorado have achieved Tree City USA status, including Boulder, Commerce City, Steamboat Springs, and Pueblo.
The city is not the only one working to preserve the environment in Colorado Springs. Students for Environmental Awareness and Sustainability (SEAS) is an organization at the University of Colorado, Colorado Springs that works to implement sustainable practices, according to its website.
Jenna Morrow joined the club in August 2019 and was the co-president during the spring 2021 semester. During Morrow’s time at SEAS, the group was focused on the Colorado Springs Utilities Electric Integrated Resource plan.
“We were focused on making sure that for the next five years there would be a just transition to renewable and sustainable forms of energy,” Morrow said.
Morrow also focused on working to ensure that the Tree of Peace on campus was not moved, as there was talk of moving the tree. According to The Scribe, the student newspaper at UCCS, the Tree of Peace “symbolizes and solidifies the relationship between the Native American community and the entire campus community, representing a link to cultural continuity and peaceful, supportive, ongoing relationships.” The Scribe wrote that the Tree of Peace was planted in 1988 but died, and the new Tree of Peace was recognized in its place in the early 2000s.
Asked why the original Tree of Peace died, Murrow said that she was not on campus when the tree died and cannot give a definite answer, but that if she had to guess, moving the tree may have been related to its death. “Anytime you move an older, established tree, the chances of survival are not very high,” Murrow said. She reiterated that she was not sure of the exact reason.
Much of Boulder, especially the areas surrounding the University of Colorado Boulder, has a tree equity score of 100, but the city still has some disparities.
University Hill, a popular neighborhood for CU students, has a tree equity score of 100 and peak temperatures of 88 degrees Fahrenheit. Marshall, an unincorporated community located south of the university in Boulder County has a tree equity score of just 42. Peak temperatures in Marshall are 92 degrees Fahrenheit.
The PLAY Boulder Foundation established The Tree Trust, which is a program that works with Boulder residents to “promote a healthy urban canopy for years to come,” according to its website. As part of the program, a Tree Tender will go to a resident’s house and assist them with tending to current privately-owned trees or planting new trees.
Why are there such disparities
Ean Thomas Tafoya is the Colorado field advocate for GreenLatinos, a national nonprofit organization of Latino leaders that work to address issues impacting the health and welfare of the Latino community.
Tafoya, who ran for Denver City Council on the issue of tree equity in 2015, suspects that the lack of trees in some parts of Colorado has to do partly with the fact that some people are renters rather than owners, and the decision to plant a tree usually comes from an owner, not a renter. Tafoya also mentioned business accountability and cost as potential partial reasons why there is a lack of trees in some areas of Colorado.
“I do think we need some sort of strategy that brings business, government, and the people together to improve tree canopy cover,” Tafoya said. The block Tafoya grew up on had only one large tree.
Austin Troy, the chair of the Urban and Regional Planning Department at the University of Colorado Denver, said that one reason Commerce City specifically may have such a low tree canopy cover could be because Commerce City has more non-residential land use than other areas of Colorado.
“Trees often don’t survive very well in areas that don’t have a strong residential component,” said Troy. This is because industrial areas often don’t have as much of a demand for trees as residential areas, and because there may not be someone to take care of the trees in non-residential areas. Additionally, industrial areas might not have planting conditions that are as good as in residential areas.
When asked what could be done to combat the tree canopy cover disparities between high-income and low-income areas, Troy mentioned planting more trees in areas with lower socioeconomic status, but also acknowledged that simply planting more trees is often not enough, as there needs to be someone to take care of the trees. Troy said that getting stewardship organizations that have professional experience with tree care and maintenance involved in areas with low tree canopy could help.
A paper published in the scientific journal PLOS One found that low-income census blocks have, on average, 15.2% less tree cover than high-income census blocks. The study also found that the low-income census blocks are approximately 1.5 degrees Celsius hotter than high-income census blocks.
Driven by climate change, average temperatures in many parts of Colorado have already risen several degrees above pre-industrial levels, and are expected to continue to rise in the coming decades. That’s why many advocates believe that improving tree cover and reducing the urban heat island effect is an important component of climate policy.
“Trees have a broader, global effect by helping mitigate climate change and slow down the increased temperatures,” David said.
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