Saving the trees: Decades of work lead to UTC faculty publication in Science

Hill Craddock stands among rows of young American chestnut trees inside a greenhouse, examining the plants as part of ongoing research and restoration efforts. White identification tags mark individual seedlings growing in black pots beneath the curved greenhouse structure.

Dr. Hill Craddock stands among American chestnut tree saplings in the Fortwood Street Greenhouse. Photo by Angela Foster.

The first American chestnut tree Dr. Hill Craddock ever saw was one he grew himself.

He was about 15 years old, working out of a small greenhouse his father built beside their home. A neighbor gave him a handful of chestnut seeds and suggested Craddock try growing them.

Craddock followed the instructions he found in a gardening book, storing the seeds in the refrigerator to mimic winter conditions before planting them. Months later, something took root.

“The tree in my dad’s yard got very large, eventually about two feet in diameter and maybe 40 feet tall,” Craddock said. “It got blight, which killed it back to the ground.”

When he planted it, it was just an experiment. It didn’t stay that way.

More than four decades later, Craddock, now a UC Foundation Robert M. Davenport Professor of Biology at the University of Tennessee at Chattanooga, is part of a team whose work was published in Science, one of the world’s leading scientific journals.

The paper, “Genomic approaches to accelerate American chestnut restoration,” shows a major step in a decades-long effort to restore a species that once dominated forests across the eastern United States.

“It really is the culmination of 30 years’ work,” Craddock said about the publication.

The American chestnut’s disappearance is one of the most significant ecological losses in North American history. The fungal disease was first identified in New York in 1904.

“It was a forester who noticed that the trees at the Bronx Zoo were dying,” Craddock explained. “He collected some samples and sent them off and nobody knew what was killing them. Nobody had ever seen anything like that. The trees in the Bronx Zoo were a hundred years old, giant trees.”

By the 1930s, the blight had spread to Chattanooga. Within a few decades, billions of trees were dead.

“It’s difficult for us to imagine the scale and the scope of the disaster,” Craddock said.

While the species has not vanished completely, it fell into the category of “functionally extinct,” he said. Root systems survive underground, sending up shoots that grow before dying from the same disease.

Over time, the cycle had prevented the trees from reproducing in a way that would sustain the population.

“There’s been a cycle of sprouting and blighting over the last hundred years or so,” he said.

The research published in Science is part of an effort to change that outcome. Using genomic tools, scientists are working to identify and breed trees with stronger disease resistance.

Craddock’s work starts at the very beginning.

“My main contribution is growing the plants,” he said. “When the genetic engineers or genomics experts need the plant, they would come to me to get it.”

It involves collecting plant material, cloning trees and carefully controlling conditions so researchers can track how different varieties respond to infection. For one phase of the study, Craddock and his team monitored changes in the trees before and after exposure to the fungus, capturing their responses at the molecular level.

The results pointed to the same solution.

“It’s complicated,” he said.

Instead of one gene flipping the switch, resistance comes from hundreds of genes working together. Some are always active and others kick in when the tree is under stress. The complexity slowed progress, but it’s also why newer genomic tools are making such a difference.

These tools are used by the next generation of researchers, who have also found a passion for the American chestnut through their work alongside Craddock.

Two researchers stand among rows of young American chestnut trees inside a greenhouse, discussing the seedlings as they monitor plant growth. Hundreds of potted trees fill the greenhouse, with white identification tags marking individual plants used in restoration research.

Alex Harb (left) and Zach Anderson in the Fortwood Street Greenhouse.

Zach Anderson, a graduate of both the bachelor’s and master’s in environmental science programs at UTC, now serves as the southern regional science coordinator for the American Chestnut Foundation.

Anderson is responsible for coordinating research and breeding efforts across multiple states.

“Basically, I kind of oversee the science of the south,” Anderson said while working at the Fortwood Street Greenhouse on UTC’s campus.

That involves managing large trials designed to compare how trees perform under different environmental conditions.

“This is a common garden study because we’re trying to tease out environmental factors such as sunlight, temperature and rain variation,” he explained. “We tease out those variables and then we get the data to make selections.”

The selections are heavily guided by genomic data, allowing researchers to identify promising trees earlier and move them into the next stage of breeding more quickly.

“Based on the genomic tools … we can predict which ones have the most resistance and not even inoculate them at all,” he said.

Anderson first encountered the tree in class.

“It wasn’t even a tree that I was aware of,” he said. “It wasn’t until Dr. Craddock’s dendrology class when he mentioned he was having some volunteer days.”

Over the next few years, he went from a volunteer to a leadership role in regional research.

“I fell in love with the tree and fell in love with the people,” Anderson said.

Alex Harb is also a graduate of both UTC programs. He started as a volunteer and now spends much of his time working in the greenhouse as a plant waterer.

“Well, that’s the official job,” Harb said with a laugh. “It’s more of do whatever Dr. Craddock says.”

During the summer, the work becomes constant.

“It is every single day, seven days a week,” he said.

The day-to-day tasks like watering, moving plants and helping with trials are repetitive, but it’s what the research and restoration depend on.

“I’ve always really liked plants and trees,” Harb said. “Then I took some of Dr. Craddock’s classes and he gave the whole spiel: ‘Oh my gosh, American chestnuts, they’re the best tree ever.’

“Then I came up here, volunteered, and now I’m here every day. And I don’t regret it.”