Want to beat the heat? Start with trees

People rarely give much thought to the trees around them — until there aren’t any.

Not when they're driving past them. Not when they're scrolling on a park bench. But on a sweltering Miami afternoon, when the sidewalk feels like a frying pan and the air itself seems to radiate heat, stepping beneath a tree can feel like walking into a different climate. A cooler, more welcoming climate.

That's exactly what Florida International University researchers have spent the past several years studying. Their conclusions could change the way people think about urban trees. They are more than just landscaping, according to FIU biologist Christopher Baraloto. Trees should be thought of as critical infrastructure, he said.

Baraloto is the director of the International Center for Tropical Botany at the Kampong — a collaboration between FIU and the National Tropical Botanical Garden. This summer, he has felt the heat. All of Miami has. Throughout Miami-Dade County, residents just experienced one of the longest streaks of consecutive 90+ degree days on record. Heat indices, which take into account temperature and humidity, have exceeded triple digits. Simply put, it’s hot. In neighborhoods dominated by asphalt, concrete and rooftops, the urban heat island effect can make it feel even hotter.

“I hope everyone can recognize the value of trees for their ecological benefits including cooling and stormwater mitigation,” Baraloto said. “If we start with that premise, I believe we can have the conversations needed to support healthy, vibrant communities.”

Baraloto leads a research team in FIU’s Institute of Environment comprised of scientists from the Departments of Biological Sciences and Earth and Environment. Their research indicates trees can cool urban areas by as much as 10 degrees, but not all trees are equal when it comes to cooling capacity. A young tree will not cool in the same way a large, older tree can, according to Madison Kinder, an urban ecology fellow in the Institute of Environment. She is currently researching the effects trees have on communities including how they can reduce UV exposure.

Drawing on more than two years of temperature monitoring, inventories of more than 9,000 urban trees, countywide canopy analyses, and a survey of 600 residents, FIU researchers say the benefits of trees depend on a variety of factors. It matters what trees are planted, how large they become, where they grow, and whether mature canopy is protected, according to Paulo Olivas, assistant professor of Earth and Environment. In other words, it’s about more than just planting trees.

Trees with large, dense canopies, like native fig trees, produce more cooling. Palm trees and ornamental trees like the royal poinciana produce less. For Baraloto, it’s all about balance. He led a comprehensive inventory of Coconut Grove’s street trees and found remarkably high species diversity. However, Miami’s street-tree diversity largely comes from palms and other species that contribute limited canopy. A smaller number of large trees, including native live oak and gumbo limbo, currently account for the disproportionate share of street-level canopy.

“A diverse urban forest is desirable, but diversity, tree numbers, and ecological function are not interchangeable,” Baraloto said. “Protecting existing large trees while selecting species capable of developing substantial crowns could matter as much as increasing the number of trees planted.”

Miami-Dade County has about 20 percent tree canopy coverage, according to 2022 data from FIU’s Geographic Information Systems Center. That is well below the 30 percent goal set by county officials.

“We urgently need an updated assessment of today’s urban tree canopy to understand where the tree-scape is changing, how it is changing and why,” said Jennifer Fu, director of the FIU Coastal Environmental Data and GIS Center.

Baraloto was recently appointed to the City of Miami’s Tree Ordinance Advisory Committee, which was established to review the city's tree preservation and protection regulations and provide recommendations to support healthy tree populations. The city is hosting five community workshops this month for residents to learn more, ask questions and share feedback. One thing Baraloto hopes to influence is mitigation policy that balances development and Miami's tree canopy.

“Miami’s urban forest is already doing important work protecting residents from extreme heat, but what we need now are mitigation requirements that better reflect what is being lost, smarter species selection and targeted investment in neighborhoods that need shade the most,” Baraloto said.

The FIU research is conducted in partnership with community organizations across Miami-Dade County. The work is supported by the William R. Kenan, Jr. Charitable Trust, the Korth Family Foundation, the Dr. Michael and Diane Rosenberg Family Foundation, and a Florida Urban and Community Forestry grant from the U.S. Forest Service.