The Trees of Tree Town
Ann Arbor, known as “Tree Town,” loves its trees. And why not? Those leafy sidewalk sentinels are important members of the community.
Consider this: According to the city’s urban forest management plan, each public tree is worth $47.55 in energy savings per year. Each tree reduces our annual energy bill by that amount when it shades a building in the summer, cools the summer air through evapotranspiration, and buffers chilly winter winds.
Energy savings represent the biggest monetary benefit that we get from our trees—a grand total of $2,250,000 every year in Ann Arbor, courtesy of the city’s urban forest.
Trees also improve public health, and not just because they provide shade. They intercept storm water, which keeps pollutants from contaminating the Huron River—the city’s primary drinking water source—and local streams at a savings of $10.98 per tree. They also improve air quality ($8.35 per tree) and offer natural beauty, which increases property values, encourages outdoor exercise, and reduces mental fatigue ($28.89 per tree). And they provide a slew of other benefits, both tangible and intangible.
But these health benefits and financial incentives are not equally available to everyone, because trees are not distributed evenly among neighborhoods in the city. Fortunately, people like LSA alumnae Jen Kullgren (’07, M.S. ’13, M.U.P. ’13) and Alyssa Yang (’10, M.P.H. ’13) spent time searching for solutions to this problem.
Kullgren, who graduated from LSA’s Program in the Environment, and Yang, who studied sociology and cognitive science, spent the summer of 2012 working on a health impact assessment of Ann Arbor’s trees. They helped figure out whether expanding the tree canopy in Ann Arbor could improve public health in the community.
During her internship with the city, Yang scoured scientific articles to see if research actually shows that trees have a positive effect on human health. The answer was yes, with the strongest evidence linking the presence of trees to lower rates of obesity.
Kullgren worked with a team of four other U-M master’s students in the Taubman College of Architecture and Urban Planning, poring over maps of Ann Arbor neighborhoods and creating a plan to fix the unequal distribution of trees.
“Ann Arbor is fortunate enough to have funding sources dedicated to data collection,” Kullgren says, and her team used maps of the urban forest that the city had drawn up a few years before. In 2010, the city got an aerial view of tree canopy cover across the landscape by gathering high-resolution photos on airplane flyovers. “The tree canopy cover is a bird’s-eye view of how much of a neighborhood is covered with leaves in the summertime,” Kullgren explains.
She and her team compared the tree canopy maps to human demographic maps of Ann Arbor neighborhoods. They used census data (including resident density, income, percent of residents receiving federal subsidies, and percent in poverty) to see where in Ann Arbor public health threats (like obesity and asthma) loom larger for people. Then, Kullgren says, they “overlaid those maps with tree canopy cover maps to look at: Where are the most vulnerable populations? And where’s the lowest tree canopy cover?” The two factors often overlapped. The more vulnerable neighborhoods tended to have fewer trees. In those areas, Kullgren’s group recommended that the city focus its tree-planting efforts to create healthier environments.
“The best part of the project was how multidisciplinary it was,” says Yang. “It was a great experience to work at the intersection of public health and urban planning.”
Last year, the city of Ann Arbor adopted an urban and community forest management plan that includes ideas stemming from Kullgren’s and Yang’s work. By planting new trees in strategic locations, the city can more equitably spread health and wealth among its residents. For every $1 spent on the forestry program, the community gains $2.68 in public health benefits.
While those are good returns, it’s a long-term investment. It takes about 20 years for each new tree to contribute meaningfully to the urban canopy. In the meantime, Yang and Kullgren have taken their efforts to other communities. Yang has a fellowship with Wisconsin’s Department of Health Services, where her work focuses on chronic disease and maternal and child health. Kullgren works with a nonprofit in Pittsburgh to support neighborhood organizations’ efforts to enhance the urban forest throughout the city.
“It’s cool to see the connection between tree canopy cover and health impacts,” says Kullgren. “Providing a connected greening experience to people who are living in a dense urban area is something that I’m really excited about and interested in.”
This article is part of a larger environmental series in honor of the 45th anniversary of Earth Day. U-M kicked off the first nationwide Earth Day in 1970 by hosting a teach-in that drew more than 50,000 people. Also in this series: