The urban canopy that blankets the Wasatch Front is more “supernatural” than “natural,” said Salt Lake City Urban Forestry Director Tony Gliot. Few trees existed across the valley when Mormon Pioneers arrived in 1847. But as the human-planted forest rapidly proliferated after settlement creating a richly diverse urban forest of mostly non-native tree species, the forest functions to shade, protect, nourish and beautify our neighborhoods.

As our cities become hotter with climate change, how can the urban Wasatch Front ensure that trees today will remain healthy and viable in the coming decades?

On Sept. 23, the Wilkes Center for Climate Science and Policy and Red Butte Garden and Arboretum co-hosted a panel discussion with urban tree experts to discuss strategies for maintaining a healthy urban forest in the face of increasing extreme heat events and climate change.

Sarah Hinners, director of conservation and research for Red Butte Garden and Arboretum, guided the discussion with Gliot; Red Butte Arborist Charlie Perington; and City & Metropolitan Planning Associate Professor Alexandra Ponette-Gonzalez.

“Supernatural forests”

Gliot said while we all want to save the Great Salt Lake, maintaining a healthy urban forest is a challenge coming to the forefront. “We have to engage with our tree stewards, which is every person in the city, to find that balance of maintaining one precious resource (our water) with another precious resource—our trees.”

“The cat’s out of the bag with species diversity. We can’t emphasize planting natives anymore,” said Gliot, who said except for the urban-wildland interface areas where native trees are still prevalent, planted non-native trees now comprise the vast diversity we live with.

Alexandra Ponette-Gonzalez, who is also curator of urban ecology at the Natural History Museum of Utah, shared her research studying how trees capture particulate matter air pollution in Salt Lake City, Eugene, Oregon, and Cleveland, Ohio.  “We’re asking, how much do the trees capture?  Where do they capture the most?  What species are the best for this? How does it vary from tree to tree?”

Challenges facing urban forests

The panel discussed some key challenges and some guidelines for solutions facing Utah urban forests and those caring for them:

How much to water?
Better research is needed to determine evapotranspiration—how much water a given tree moves water from the ground into the air. Gliot remembered a recent Utah conference of arborists, “where you had probably 150 arborists in the room, and nobody could agree on how to tell people how to water a tree! It’s not rocket science, it’s a little harder than rocket science!”

Stands over solitary trees
Perington noted that as the urban landscape changes, developers can improve project outcomes by preserving stands of trees that can collectively shade themselves to reduce the stresses as opposed to solitary trees. “For a future climate, having a group of trees that can maintain themselves would be a practical use of design,” he said. Gliot added that while it’s common practice to plant the largest tree species they can get at maturity, urban foresters are constrained by zoning, plots and political boundaries which don’t always allow growing large canopies. “Generally speaking, a larger canopy provides better benefits,” he said.

Air pollution hurts trees
Ponette-Gonzalez said we tend to focus on the services urban trees provide humans without asking how trees fare in harsh urban environments. “We know there is a spectrum. We know there will be plants that are more sensitive and tolerant (to air pollution). And sometimes they’re not native. And maybe we like them and maybe we don’t. Our preferences may not always match with the (resiliency) of the plants themselves.”

Tree inequity
Ponette-Gonzalez raised the concern of tree inequity, the uneven distribution of and access to urban trees across city landscapes. “Tree equity isn’t just planting trees on someone’s corner; it also means people can participate in those planting decisions. It also involves recognizing that people have different ideas for what trees they want, or maybe don’t want.” Gliot said tree equity has been a hot topic in the arborist profession and a lot of Federal funds have been invested toward future tree equity in cities.

Seeing the forest for the trees
“Plant blindness” is the phenomenon of overlooking plants as living organisms in one’s everyday life. The group agreed that personal connections to trees make a difference in the overall health and sustainability of urban trees. “Every tree needs a person,” quipped Ponette-Gonzalez. Moreover, an emphasis on long-term care for established trees versus planting new trees is needed. “Planting a tree feels good, but how do we make checking on the tree feel great?” asked Perington. Gliot added the average lifespan of an urban tree is 7~10 years. “We could grow trees that live longer if we pay more attention to them.”

Salt Lake City Urban Forestry provides a list of suggested trees and other information. They encourage residents to call with specific questions and concerns.

Watch the recording of the discussion here.

• Ross Chambless Community Engagement Manager, Wilkes Center for Climate Science & Policy
  (801) 646-6067 ross.chambless@utah.edu