The American yellowwood experiment, one year in

Almost exactly a year ago, 100 tiny American yellowwood tree seedlings were planted and stood whipping in wintry winds on a sloping hill behind Carnegie Mellon University in Schenley Park.

The Pittsburgh Parks Conservancy had created a living laboratory in which to monitor the future viability of this species in this climate zone.

The American yellowwood grows most naturally in the more hospitable zone that stretches from Oklahoma to North Carolina. But with temperatures expected to change in our zone over the next century, the gamble is that the yellowwood can thrive here one day.

Ten known specimens are already growing in the Pittsburgh area. The conservancy collected seeds from those trees to plant in the Schenley Park “Fezziwig” Tree Research Grove.

Fezziwig was a character in Charles Dickens’ classic “A Christmas Carol,” a generous mentor of Ebeneezer Scrooge. He was chosen as the namesake of this grove by the man who made the research possible — Tor Richter, a retired Navy physician who donated the money for the conservancy to undertake the long-term mission.

Dr. Richter, who lives in Oakland, decided several years ago to consider designating some of his money for a charitable project.

“I was thinking along the lines of stormwater run-off control, and I am interested in genetics,” he said. “I live a block or so from Schenley Plaza and I saw the conservancy make a park out of a parking lot. I got to talking to them.”

Phil Gruszka, the conservancy’s director of horticulture and forestry, said the existing mature specimens — in Schenley and Mellon parks as well as on private properties in the area — offer hope for the strongest of the saplings in the research grove.

Four-foot deep swaths of sand along a terrace above the grove absorb rainwater, and a network of pipes feeds that water to the trees.

A member of the pea family, the yellowwood has drooping, fragrant white blossoms and yellow autumn foliage. Its presence in northern states may indicate that the species once had a wider range and that the fittest survived conditions that pushed the others out, Mr. Gruszka said.

“The most important thing is when they break bud,” he said during a visit to the grove this week.

Yellowwoods that leaf out too early in northern states can develop a canker disease from being zapped by late frosts. This disease has kept nurseries from growing them for sale in the region, he said.

Late last April, conservancy staff checked the saplings and noted which ones had budded, which ones had leafed out and which ones showed no change.

“We came back right after Labor Day and measured their height,” Mr. Gruszka said.

Vigorous growth isn’t necessarily an indication of success, he said. More suggestive of success for selection is the shape that the tree is taking, including branches that emerge at a 70 degree angle.

“We’re not dismissing any trees yet because it will take years of data before we make our final selection,” he said. “The ones that are lagging will catch up.”

Research will include gene sequencing to determine how diverse this range of specimens is, he said. Each tree will have its own identity, the way people have individual fingerprints.

The conservancy will ultimately seek a patent on its results and expects to supply the nursery industry with its specimens. Proceeds of the sales will return to the city of Pittsburgh, Mr. Gruszka said.

He stopped to finger the leaf of one specimen that is three and a half feet tall already.

“The yellowwood is not known as a fast growing tree,” he said. “This one’s buds had broken in April and it was 34 inches tall on Labor Day. It has a good central stem and good branch angles.”

About nine of the trees appeared to be dead, and Mr. Gruszka said some may have been the victims of mice. The rodents like to nibble the cambium layer just under the bark surface. That’s where cell division happens, helping the tree to grow.

The conservancy’s gardener, Jaci Bruschi, has been caring for the grove, keeping the grass cut so that raptors can easily see mice that venture into it.

Ms. Bruschi also watered the trees the first year, but now they are on their own — left to prove which among them are toughest, Mr. Gruszka said.

Among the 100 saplings, the number that show the most resilient qualities will be chosen for continued research. The others will be transplanted throughout the park system, he said.

Mr. Gruszka said most nursery trees are propagated from cuttings, grafts or tissue culture to create certain qualities, which make them clones. The conservancy’s goal with the yellowwoods is to ensure that they have heirs, he said.

Dr. Richter hopes the grove “will be a place that will bring botanists, with potential for everyone from kids to college students to study and talk about plant genetics.”

Diana Nelson Jones:

First Published November 8, 2020, 6:00am