A new study ranks live oaks and American sycamores as the champions among 17 affectionately-named “super trees,” based on their ability to facilitate infiltration, stabilize the landscape during floods, mitigate urban heat, and soak up carbon dioxide and other pollutants.
The research comes from a collaborative group of Texas universities: at Rice University, the Houston Health Department’s environmental division and Houston Wilderness.
The open access study in the journal Plants People Planet — led by Houston Wilderness President Deborah January-Bevers and colleagues at Rice and in city government — lays out a three-part framework for deciding what trees are the right ones to plant, how to identify places where planting will have the highest impact and how to engage with community leadership to make the planting project a reality.
Using Houston as a best-case example, the collaborators determined what trees would work best in the city based on their ability to drink in water, stabilize the landscape during floods, soak up carbon dioxide and other pollutants, and provide a canopy to mitigate heat.
With that information, the organizers ultimately identified a site to test their ideas. With cooperation from the city and nonprofit and corporate landowners, they planted 7,500 super trees on several sites near the Clinton Park neighborhood and adjacent to the Houston Ship Channel. Along with planting native trees, the partners conducted a tree inventory and removed invasive species.
Rice alumna Laura Campos, a data scientist in the Department of Statistics, was brought into the project to create maps that showed where mass plantings would have the most impact.
“These maps help people understand that their little pocket neighborhoods are connected to the bigger picture,” Campos said. “They help us bring in all the players to get them to realize how everything is interconnected and how public health can benefit with every step forward.”
Ranking the species’ talents to soak up pollutants, provide flood mitigation and cool “urban heat islands” helped them eliminate most of the 54 native trees they evaluated. Ultimately, they narrowed the list to 17 super trees, with live oak and American sycamore on top.
Live oaks were No. 1 for their ability to soak up pollutants across the board. The No. 2 sycamore was less able to pull in carbon but excelled at grabbing other pollutants, flood remediation and reducing heat on the ground with its wide canopy.
Some super trees — particularly live oak, American sycamore, red maple and laurel oak — are adept at pulling ozone, nitrogen oxides, carbon monoxide, sulfur dioxide, and particular matter 2.5 microns and smaller from the air. That helps determine where they can be deployed to have maximum impact on neighborhood health.
“We’re still running the program, with over 15,000 native super trees now planted along the ship channel, and it’s incredibly popular,” January-Bevers said, crediting Hopkins with the push to issue a study that could help other communities. “It’s benefiting our city in regions that are critical for air quality, water absorption and carbon sequestration.”
Hopkins said the contribution by Rice — a “Tree Campus USA” and an arboretum in its own right — was important in setting a tree-ranking method that could influence environmental strategies just as well in other cities.
