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The trees aren’t native to the Pittsburgh area, but they’ve largely thrived in Fezziwig Grove, a research grove manned by the Pittsburgh Parks Conservancy.

As the conservancy’s horticultural project manager, Bruschi is tasked with caring for the yellowwoods and collecting data on how they grow, what form their branches take and when their leaves emerge each spring.

It’s part of an effort to see how well yellowwoods — which are native to Kentucky — can grow in Pittsburgh.

The goal is to diversify tree species in the area and begin identifying trees that could be better suited to a changing climate, said Phil Gruszka, who worked on the grove before retiring from his post as the conservancy’s director of forestry.

Some yellowwoods live in Pittsburgh outside of the research project now, Bruschi said. Researchers collected samples of local yellowwoods to use for the research grove.

The idea behind the effort is twofold: Examine yellowwoods as a tree that potentially could be well-suited for Pittsburgh amid global climate change; and encourage diversity to create an urban tree canopy that is more resilient to diseases and pests.

Gruszka said climate change could impact what kinds of trees are best able to live in the region. Some trees that do well here now may struggle to survive if temperatures continue to rise, he said, while other trees that now live in warmer climates might do well in this region as it heats up.

“We were looking at native species that grow south of the Pittsburgh area and beginning to look at which of those species could we be looking at for the future urban forest of Pittsburgh,” he said. “Yellowwood popped right to the top of our list.”

Because it’s native to southern parts of the country, he said, it can withstand warmer temperatures. It also has few insect or disease problems and doesn’t harm Pittsburgh’s native plants and animals, Gruszka said.

The concept of introducing trees like yellowwoods is known as assisted forest migration, he explained. That’s when researchers handpick trees that could sustainably replenish a region’s tree population, particularly if climate conditions impact which species would be best suited for an area over time.

Gruszka said they’re looking hundreds of years into the future.

“The people who live here 100 years from now are going to want to enjoy their parks and their urban forest as much as the people now,” he said. “We have an obligation to make sure that happens.”

Seeking tough trees

Already, Bruschi said, there are early signs that a changing climate — with warmer temperatures and stronger storms — could be stressing some local native trees.

Serviceberry trees, known for their white flowers and red berries, have been struggling in Pittsburgh parks recently, she said.

Increasingly harsh storms, she said, can damage trees with weak bark. And some trees here that already are on the warmer end of their spectrums may suffer during hot, dry summers.

There are indications that the Pittsburgh area is warming.

The average summertime temperature last year was 72.1 degrees, up from 69.9 degrees on average in 1950, said Colton Milbarek, a meteorologist with the National Weather Service in Moon.

During that same period, average overnight low temperatures rose to 62.3 degrees from 59.2 degrees.

Brian Wolyniak, an urban and community forestry expert with Penn State Extension, said studies have indicated the Pittsburgh region likely will see changes to its tree makeup because of climate change — but it’ll happen slowly.

“It won’t be like a flip of a switch, but that change in weather conditions is going to outpace the rate that you have adaptation within a particular species to adapt to the warmer temperatures,” Wolyniak said, so introducing species that are predisposed to warmer climates could help aid the transition.

The impacts of heat and drought are particularly harsh on trees in urban environments, Wolyniak said.

Urban areas with lots of development tend to be hotter than more rural areas, and trees planted along sidewalks and roadways often can’t build out extensive root networks to draw up water.

“In these cases, we’re looking for trees that are essentially tough, that can stand up to these conditions,” he said.

‘Crucial’ diversity

The second key element to the Fezziwig Grove project, Gruszka said, is to bolster tree diversity.

Diseases and insects can hurt some trees more than others. Having a variety of tree species — and genetic diversity even within the same species — ensures that not all trees are wiped out by a single threat, he said.

The yellowwoods at Fezziwig Grove come from several different mother trees, he said, so they’re not all identical, and thus not equally prone to the worst effects of diseases or other harms.

“The genetic diversity within a tree population is really crucial,” he said.

Wolyniak cited as an example how emerald ash borers wiped out huge swaths of ash trees — and if that was the only tree planted in an area, they could all be wiped out because of that one insect.

Similarly, American elms were hit hard by Dutch elm disease.

But other species, Wolyniak said, survive scourges that plague only specific trees.

“We’re finally learning we can’t over-rely on just a few species,” he said.

So far, Bruschi said, none of the yellowwood trees at Fezziwig Grove have succumbed to any type of disease.

Bud break

The first 100 saplings, about a foot tall, were planted in 2019. Another 100 were planted in 2022.

Now, the largest stands around 12 feet tall.

Half are alive today in their small grove off of Frew Street near the Bob O’Connor Golf Course, Bruschi said. The others were eaten by deer, bunnies, voles and groundhogs while still saplings.

Some of the trees that initially seemed to be dead after animals munched on them surprised Bruschi by rebounding. She said she had made notes that some were surely dead only to see them spring back to life the next season.

Bruschi said some of the trees show signs of chlorosis — identified by yellowing leaves — which is caused by nutrient deficiencies.

Bruschi is focusing on monitoring several elements that reveal which of the trees could be most resilient and easiest to maintain.

One key factor is bud break, or when leaves break dormancy in the spring. Trees that break bud later in the season, she said, may be more favorable in Pittsburgh, where late season frosts can hurt trees that bud too early.

She’s also looking at the form of the trees, or how their limbs take shape. Some yellowwood branches split off very close to the ground, making the tree more susceptible to wind and ice damage.

The trees that show the best traits, Bruschi said, are the ones that should be propagated.

Though Bruschi is looking at the trees mostly through a scientific lens, she noted they also have perks anyone could easily recognize. Once they’re mature, they present sweet-smelling white flowers that many people — and pollinators — enjoy.

They grow to about 30 or 50 feet tall, offering plenty of shade.

Bruschi said she was drawn to the yellowwood research because it’s a “more forward-thinking” initiative that lets her “think outside the box” about how to improve the tree canopy for future generations.

The research has other fans, including Tor Richter of Pittsburgh’s Oakland neighborhood, a retired Navy doctor who has donated to the conservancy to support this research. He described yellowwoods as “good-looking trees.”

He became interested in genetic diversity after reading about a similar study. He said he’s become passionate about trees and green space since he can see Schenley Park from his Oakland home.

Richter said he’s hopeful the research will help identify the best samples of the species and help the conservancy spread them successfully throughout the city so others can enjoy them, too.

Steel City magnolias?

When foresters plant trees, they often prefer native over non-native options like yellowwoods, Wolyniak said.

Native plants, he said, tend to be best adapted to live in an ecosystem. And it’s important to avoid introducing invasive species that can run rampant and harm native wildlife — though yellowwoods aren’t considered invasive.

But when planting in urban environments, Wolyniak said, sometimes non-natives from a warmer climate are a good choice, better able to withstand hotter conditions and reflected heat.

When it comes to planting trees in artificial environments — like in cement sidewalks — natives aren’t always viable options. Some local trees don’t hold up very well outside of the woods, Wolyniak said.

“We kind of joke, ‘What’s native to a concrete box cut out in the sidewalk?’ ” Wolyniak said.

When it comes to yellowwood in Pittsburgh, he said, “It may not be native, but it would do well.”

Over the next few years, Bruschi said, the conservancy could start to disperse the trees throughout Pittsburgh parks. The nonprofit will continue to monitor them and collect data from their new homes.

The conservancy also may look to conduct further studies on genetic diversity among the tree samples they’ve been analyzing, she said.

Yellowwoods may be just the beginning, Gruszka said. He said the conservancy could look to expand its research to other trees that could be good candidates for the city.

Magnolias, he said, seem like a promising lead.