By Allan Britnell

Reforesting vast swaths of eastern North America with a hybrid version of the American chestnut (Castanea dentata) could lead to a revival of this endangered species, as well as offer a potential solution to climate change.

The towering icon, which can reach heights of 30 metres, was once the dominant species in many forests throughout the eastern United States and southern Ontario. But in the 1920s, the chestnut blight fungus, probably introduced by imported Asian chestnut trees, reached Ontario, and by the middle of the century the disease had killed around four billion trees (1.5–2 million in Ontario alone), virtually wiping out the species in North America.

Today, fewer than 150 mature chestnut trees are estimated to remain in southern Ontario, all found in the narrow Carolinian band between Windsor and Niagara Falls, an area in which farming and suburban sprawl continually reduce the available habitat.

Forestry researchers have tried various techniques to help resurrect the species over the past century, but only now do they think they have a viable option. Douglass Jacobs, an associate professor at Indiana’s Purdue University, has hybridized blight-resistant Chinese chestnut strains with American chestnuts. By “backcross breeding” an initial Chinese-American hybrid with pure American chestnut trees, Jacobs has developed a hybrid that he estimates is 94 percent American chestnut. He expects that his hybrids will be ready for widespread planting within the next decade, and that within 50 to 100 years the species could again be a common sight in eastern forests.

While Jacobs readily admits that these hybrids “cannot technically be considered pure American chestnut” and that “could raise questions by those concerned with influences of alien invasions on ecosystem integrity …, compared to the alternative of losing American chestnut entirely … most people accept this backcross hybrid as a native species.”

Sean Fox, horticulturist at the University of Guelph’s Arboretum, says that he is on the fence about introducing hybrids. “It’s not the ideal solution, but I couldn’t come up with a better one to help save the species.” The problem with chestnuts, Fox says, is that, unlike with elms in the Arboretum’s famed Elm Recovery Project, with chestnuts “there’s very, very little genetic stock left to work with.” As a result, hybridization is seen to be a last-ditch effort to revive the species.

As an incentive for accepting the hybrid, Jacobs points out that since American chestnuts grow faster and larger than most other hardwood species, it is an ideal species for sequestering carbon.