A race is underway to save Ontario’s vanishing American chestnut trees, once a dominant species in the province’s southern forests.
This summer, two undergraduate students from the University of Guelph are trekking through forests to find, tag and assess the few chestnuts that remain.
An estimated two million of the trees — known for their spiny fruit husks containing edible, glossy nuts — once covered about 70 per cent of the canopy. Today, less than one per cent remain. Most are sick and unable to reproduce after a devastating fungus arrived in the early 1900s. Without intervention, they could vanish within 150 years.
Katerina Trieselmann, a bachelor of science student in environmental biology and Caitlin Barton, entering her fourth year in zoology, are tracking the health of survivors and searching for clues about why some endure — in hopes of preventing the species from disappearing forever.
The team’s work, part of a decades-long effort supported by the Canadian Chestnut Council, aims to identify traits or environmental conditions that help some trees survive. They are also testing for the presence of a naturally occurring “hypovirus” — a type of virus that infects the blight-causing fungus and can weaken it — to see if it may be contributing to the survival of certain trees. Their research will help scientists develop strategies to save the species.
“We don’t have a silver bullet yet, but there are some positive signs,” said Brian Husband, a Guelph professor of integrative biology, who leads the research.
An estimated two million of the trees — known for their spiny fruit husks containing edible, glossy nuts — once covered about 70 per cent of the canopy. Today, less than one per cent remain.
“A small number of Canadian trees appear to be tolerating blight at a higher rate than trees in some US populations.”
Husband said the research aim is to study whether the surviving trees’ resilience comes from environmental conditions, genetic traits or the presence of hypoviruses. Understanding these factors, he said, could help stabilize the population and support its recovery.
According to Husband, chestnut blight is a fungal disease that creates large wounds, called cankers, on the trunk and branches. These block the flow of water and nutrients, slowly starving the tree until it dies.
Although it may have been slow-moving and hard for the layperson to observe, Husband said the loss of the American chestnut was one of the big ecological catastrophes of the last century, devastating forest ecosystems and eliminating a valuable source of lumber and nuts in Ontario.
Efforts to save the tree include crossbreeding with more blight-resistant Chinese and Japanese chestnuts, traditional breeding programs in Canada and lab-based genetic modification in the US. While some trees with greater tolerance have been produced, Husband says they have faced setbacks when planted in the wild, as tolerance to blight doesn’t always protect them from other environmental stresses.
Another strategy — introducing hypoviruses that infect the blight fungus and weaken it — has worked in Europe, where chestnut forests have made a strong recovery, Husband said. In North America, however, it has shown only patchy results in a few local areas, and there’s no strong evidence it can work as a large-scale recovery strategy.
This summer’s research includes testing healthier-looking trees in Ontario for signs of the hypovirus, he added.
Much of Trieselmann and Barton’s summer was spent in Norfolk and Haldimand counties, home to one of the densest concentrations of remaining chestnuts. At Backus Woods, they had their most productive day — confirming dozens of living trees and even discovering new ones, which they tagged for future monitoring.
Trieselmann says many chestnuts were smaller than people expect — often around five metres tall, compared to the 20 to 30 metres they could reach before blight — because older trees have died back and new stems rarely reach maturity before the disease finds them.
She also worries that even healthy-looking trees often aren’t producing flowers, meaning they can’t reproduce naturally. “You can have healthy trees, but if they’re not reproducing, the population can’t come back,” she said.
Both students see the long-term monitoring as critical. By tracking survival rates, health trends and environmental conditions over decades, scientists can pinpoint which populations are coping better and why. That information can guide planting programs, targeted protection and other recovery efforts.
For Trieselmann, the work is also personal. She’s passionate about conservation and believes the public can play a role. Many remaining chestnuts grow on private land, often without owners realizing they’re endangered. “Learn what’s on your land and in your community,” she said. “Sometimes, protecting a species starts with simply knowing it’s there.”
For Barton, the summer gave her valuable hands-on skills in mapping, navigation and field research, while contributing to a bigger cause. “It’s only one species,” she said, “every species counts.”
“It is a beautiful tree, and there is a lot of passion behind the effort to save it,” Husband said. “With continued work, I’m hopeful we can make a difference.”
