Chestnut trees to spread across landscape again, says Purdue scientist

A Purdue University researcher is working to restore the American chestnut, an important wildlife tree and timber resource that dominated the landscape from Maine to Mississippi before it was driven to near-extinction by a fungal disease introduced about 100 years ago.

Doug Jacobs, assistant professor of forestry in the Hardwood Tree Improvement and Regeneration Center at Purdue and director of the Indiana chapter of the American Chestnut Foundation, studies how well American chestnut trees grow in plantations, research essential to future reintroduction plans. He also is developing a blight-resistant hybrid to be used in future planting projects.

In a paper to be published in the April issue of Forest Ecology and Management, Jacobs reports that American chestnut in a study plantation grew as much as 77 percent taller and 140 percent wider than two other forest species – black walnut and northern red oak – in the same plantation over an eight-year period.

On average, the chestnut trees in the plantation grew to 6.4 meters in height, while black walnuts and northern red oaks only grew to 4.4 and 3.6 meters, respectively, in the same time period.

“This data tells us that American chestnut is such a fast-growing species that it should do very well in future restoration programs,” Jacobs said. “A lot of other species are much more sensitive, grow more slowly or just don’t make it, but this tree tends to just explode out of the ground.”

Jacobs’ research is part of a larger initiative by the American Chestnut Foundation to restore the tree to its historic range.

The species was nearly decimated by a fungal disease known as chestnut blight, which was inadvertently introduced in the United States on imported Asian chestnut seedlings. The fungus enters through injuries in the tree’s bark, spreads to the inner layers and blocks the flow of nutrients through the tree, eventually killing it.

Jacobs said the disease first appeared in 1904, and within 40 years, it had spread to every area of the tree’s range.

“Nearly every tree in the range was killed,” Jacobs said. “Ninety-nine point nine percent were killed in that 40-year period.”

The fungus persists to this day, killing chestnut trees that sprout throughout the former range. A blight-resistance breeding program, however, offers promise to re-establish the tree throughout the eastern United States, Jacobs said.

Isolated mature trees are occasionally found today in parts of the tree’s native range, and the American Chestnut Foundation’s state chapters use these trees as a resource in the breeding program, Jacobs said.

“It’s important to the program that we have trees from multiple areas,” he said. “The state chapters allow us to develop regional breeding programs to produce seed specific to the climate and other variables in different areas.”

Jacobs and his colleagues at the Hardwood Tree Improvement and Regeneration Center are developing blight-resistant hybrids for eventual planting throughout Indiana. He has established a large test stand of hybrid trees at Purdue’s Horticulture Park, and as part of his continuing work to develop a blight-resistant line, he plans to inoculate these trees with the fungus to determine their degree of resistance.

“By 2006, we expect to have blight-resistant chestnut seeds to release on a limited basis,” Jacobs said. “In another 10 to 12 years, we’ll see significant quantities of seeds planted throughout the landscape.”

The breeding program involves many generations of crosses between American chestnuts and the blight-resistant Asian chestnut, Jacobs said. By crossing hybrids, the breeding program will produce trees that are genetically 94 percent American chestnut and 6 percent Asian chestnut.

Trees with this genetic makeup exhibit the resistance of the Asian chestnut but have the growth characteristics of the American chestnut, he said.

American chestnut formerly played a vital role in the eastern forests of the United States, where it made up nearly one out of every four trees, Jacobs said.

“Chestnut is a wonderful wildlife tree,” he said. “It is unusual among forest trees in that it can be counted on to produce a good seed crop every single year – chestnuts were a valuable resource to many species of mammals and birds.”

It also was a highly prized timber tree, he said.

“Chestnut is an extremely rot-resistant wood,” Jacobs said. “Its rot-resistance, coupled with its fast growth rate and its straight form, make it an ideal tree for utility poles and mid-grade furniture production.”

Jacobs said he expects to see blight-resistant American chestnut become widely available in another 10 years and suggests that the majority of plantings be done in the Midwest, where there is an abundance of abandoned farmland.

Larry R. Severeid of the Walnut Council International Office also contributed to this research, and funding was provided by the American Chestnut Foundation and Purdue University.

Writer: Jennifer Cutraro, (765) 496-2050, jcutraro@purdue.edu
Source: Doug Jacobs, (765)494-3608, djacobs@fnr.purdue.edu
Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu
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