Institute of Energy and the Environment

'Growing Impact' explores urban forests, their impact on hot cities

The latest episode of the “Growing Impact” podcast discusses the barriers that cities could encounter when adding trees and studying if these plans for urban forests are enough to affect the warmer temperatures in cities as climate change intensifies. Credit: Brenna Buck / Penn State. Creative Commons

UNIVERSITY PARK, Pa. — The latest episode of “Growing Impact” features Travis Flohr, assistant professor of landscape architecture at Penn State. He and his team are working on a seed grant project titled “Connecting Policies to Actions for Creating Just, Biodiverse, and Climate-Resilient Urban Forests.” It is investigating the barriers cities could encounter when adding trees and studying if these plans for urban forests are enough to affect the warmer temperatures in cities as climate change intensifies. 

“Urban forests could be patches of forested land within an urban environment,” Flohr said. “But more broadly, when you talk about urban forests, you talk about the whole network of different kinds of trees and ways in which trees are represented in cities. It could be groups of trees in parks or individual trees located along streets.” 

According to Flohr, trees have been connected to reducing the urban heat island effect, which is the elevated temperatures in cities due to the replacement of vegetation with materials such as concrete or brick. These materials absorb heat from the sun and release it even after the sun has set. This can result in urban temperatures being more than 7 degrees Fahrenheit warmer than surrounding areas. 

“Because of the cooling effect of the trees and the shade they provide, we can reduce the amount of heat that is absorbed by building materials,” he said. “Additionally, that can result in less cooling, which reduces energy consumption.” 

Flohr said it has been documented that urban forests are in decline due to challenges such as pests, disease and limited access to soil and water. With fewer trees, the effects of the urban heat island will likely increase.  

But adding trees can have more impact than just reducing the temperatures in cities. Urban forests have been connected to multiple benefits, including improving air and water quality, helping control stormwater runoff, increasing real estate values, improving physical and mental health, and reducing crime rates. 

Similarly, Flohr sees a connection between urban forests and justice. For decades, many underprivileged urban communities saw disinvestments from leaders, he said. 

"The plan cannot be just going into these communities and planting trees,” he said. “It's also rebuilding relationships and trust through community work.” 

Growing Impact” is a podcast by the Institutes of Energy and the Environment (IEE). It features Penn State researchers who have been awarded IEE seed grants and discusses their foundational work as they further their projects. The podcast is available on multiple platforms, including Apple, Google, Amazon and Spotify.  

Last Updated May 1, 2023