The urban forest on Penn’s West Philadelphia campus is populated by more than 6,500 trees and in excess of 240 species of woody plants.
Sylvan lands at the University must be resilient, and able to withstand the pollution, human activity, compacted soil, poisonous salt, increased heat, and lack of water that accompanies big-city living.
“It is a challenge because urban trees have a much shorter life expectancy, so it takes a lot of extra care to really help them survive,” says Chloe Cerwinka, a landscape planner in the Office of the University Architect in the Division of Facilities and Real Estate Services (FRES). “Urban trees can have a 15-year life expectancy compared to maybe a hundred years for trees in a natural setting.”
Since 2015, the Office of the University Architect has been partnering with the Morris Arboretum on a tree donation program in which specific species of trees from the garden are planted on Penn’s campus—an arboretum itself—in order to determine how particular trees fare in an urban environment, and protect University forestry from pests and diseases as the area experiences climate change.
Close to 20 unique, young specimens have been planted since the program began, including live oak trees, Chinese ash, cherry, and Jefferson elms. Planted in March or April, the trees are placed in the ground when they are between five and 10 years old, and put in protected, interior locations on campus away from vehicular traffic, such as on College Green, Locust Walk, and by Claudia Cohen Hall.
Chinese ash trees were sprouted from seeds brought back from China by Anthony Aiello, the Arboretum’s Gayle E. Maloney Director of Horticulture and Curator. Cerwinka says the trees may be resistant to the emerald ash borer, a destructive and aggressive pest that can kill ash trees in two or three years.
“That’s really important for us to try on campus,” she says. “Hopefully we can use more of those pest- and disease-resistant trees in the future because we have a lot of ash trees within College Green. If we lost all of those, that would be a big loss for our canopy.”
Planted last spring, the live oak trees primarily grow in the South. Wide and tall with long, low-reaching branches, the trees, collected by Aiello from their northernmost occurrence in coastal Virginia, are one of the ways the University is increasing its genetic diversity to adjust to climate change.
“What we’re trying to do is plant more Southern species on the campus because it’s already starting to get warmer and these species are starting to be able to survive farther north,” Cerwinka says. “It’s great for the Morris Arboretum to be able to use our campus as a living lab to see what will survive, and to better understand how to plan for the future.”
Jason Lubar, associate director of urban forestry at the Arboretum, says the climate at Penn’s West Philadelphia campus is much different than that of the Arboretum’s in Chestnut Hill, so they are testing the trees in both locations.
“The city is within the urban heat island, so temperatures can be, on the average, four to five degrees Fahrenheit warmer downtown than they are out here on the edge of the city,” he says. “It’s almost like living in an adjacent climate zone.”
Years or even decades will pass before Arboretum and FRES staff will be able to determine if the trees from the Arboretum are able to survive in Penn’s urban environment.
“One of the things that we’re taught in landscape architecture school or in landscape and planting is that you always look 50 years ahead, if not longer,” says University Landscape Architect Bob Lundgren. “All of the trees along Locust Walk were planted 50, 60 years ago, so we have to always think much further out. It’s a long-term mindset. Come back in 50 years and we’ll tell you what we learned.”
This story originally appeared in the Nov. 16, 2017 edition of the Penn Current.
