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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Inoculating a chestnut with a slurry of hypovirus. © Robert Queen.
Inoculating a chestnut with a slurry of hypovirus. The virus is intended to kill off the fungus that causes American chestnut blight.

© Robert Queen.

August 2002

Chestnut's Last Stand

The world's largest remaining stand of American chestnut is under study and under siege in Wisconsin.

Gina Childs

The tiny organism that felled the giants
Tenuous survival in an isolated stand
Exotic invasives
Horse-chestnut vs. American chestnut
To visit the Wisconsin chestnuts

Each spring doctors come from all over the country, from West Virginia, Michigan, Maryland, and New York, to visit La Crosse, Wis. They come armed with the tools of their trade, a liquid slurry of fungi and hypovirus, a leather punch, and unrelenting optimism.

These are not medical doctors, but doctors of forest pathology and plant genetics. Their patients are not wriggling babies lined up in the halls of the local public health department; they are thousands of mammoth chestnut trees standing on 60 acres of private forestland in La Crosse County. These trees comprise the largest remaining stand of American chestnut in the world. The scientists are determined that these trees will not be the last.

Many baby boomers are too young to remember the "Redwood of the East," but the American chestnut once dominated the Eastern forest. One out of every four trees within the 200 million-acre forest that stretched from Maine to Florida and west to Ohio was a chestnut. Chestnut was so visible in the forest that during summer when the tree flowered, the Appalachians appeared snow covered. The tree earned its nickname because it grew to redwood-like proportions, sprouted readily after being cut, and its wood resisted rot.

Horse-chestnut vs. American chestnut
Horse-chestnut is often confused with American chestnut, and yet the two trees are not related. Even Henry Wadsworth Longfellow mistakenly referred to the blacksmith working under the spreading limbs of the chestnut tree when he really meant horse-chestnut.

The American chestnut, Castanea dentata, is native to the United States and belongs to the beech family. The tree has simple leaves with a serrate margin and a highly edible, one-inch nut surrounded in a prickly bur.

Horse-chestnut, Aesculus, is non-native and belongs to the buckeye family. The tree has palmately compound leaves with five leaflets. The shiny, one-inch nut is enclosed in a leathery capsule and is not recommended for human consumption.

The tree was not only prolific, it was majestic. Parks and town commons often featured chestnuts eight to nine feet in diameter. In forest situations, where trees compete stiffly for sunlight and nutrients, chestnuts could grow larger across than a dining room table and rose to heights as high as a seven-story building. Few tree species in the country today achieve this size and stature.

The tree was a staple of Eastern life. Turn of the 20th century recipes commonly included chestnut meats in their list of ingredients. Eastern farmers found harvesting chestnut fruit profitable and sent trainloads of chestnuts to Philadelphia and New York City to be roasted and sold by street vendors during the holiday season. At a time when money was scarce, the nuts sold for as much as five to eight dollars a bushel!

Native Americans and pioneers used chestnut leaves to treat whooping cough. The rot-resistant wood made excellent fence posts and barn beams. According to Don Willeke, founding member of the American Chestnut Foundation, the famed fence rails split by Abraham Lincoln were made of chestnut. On your next visit to the East, check out farms and houses on the National Historic Register – many boast beams and flooring made of chestnut. Pay attention to fine pieces of Early American furniture on the Antiques Roadshow – and you will gain an appreciation for the beauty and versatility of chestnut wood.

The tiny organism that felled the giants

So how did it happen that giant trees that were such a huge part of Eastern culture have all but disappeared from the American landscape? Dr. William MacDonald, Professor of Forest Pathology at West Virginia University, refers to the plight of the chestnut as "the single greatest catastrophe known in recorded North American forest history."

The great catastrophe began sometime at the turn of the 20th century when large, formal gardens incorporating exotic and unusual species of plants were the rage. It is likely that plant hobbyists inadvertently imported the fungus Cryphonectria parasitica when they introduced Asian chestnut varieties to the United States. In 1904, scientists discovered the fungus killing chestnut trees in New York City. Within 50 years, the fungus commonly known as chestnut blight spread throughout the entire range of chestnut, and destroyed almost all of the majestic stands of this glorious tree.

In many cases the cankers were higher up than researchers could reach safely with their ladders. Tree climbers carried the cure into the treetops to inoculate the chestnuts. © Robert Queen
In many cases the cankers were higher up than researchers could reach safely with their ladders. Tree climbers carried the cure into the treetops to inoculate the chestnuts.

© Robert Queen

American chestnut, unlike Asian chestnut varieties, has no resistance to the fungus that causes the blight. The spores of the fungus spread readily by wind, birds and mammals. Once the spores land on an American chestnut, they cause cankers on the trunk and branches. As the disease progresses, the canker encircles the tree or limb, completely cutting off the tree's ability to transport water and nutrients. Eventually everything above the canker wilts and dies. This explains why one of the first visible signs of chestnut blight is a dead or wilted branch.

Since the blight kills only the portion of tree above the canker and the tree resprouts readily, chestnut is not likely to become extinct. However, the new shoots sprouting from the stump only live for a short time until they too become blighted and die. This tree that once towered above the forest canopy has now been reduced to a shrub, altering the ecology of the Eastern forest forever.

Tenuous survival in an isolated stand

If you want to experience the unique grace and beauty of a chestnut forest, one of the few places you can do so is in La Crosse County. Featured in National Geographic and studied by the best and brightest forest pathologists in the country, approximately 2,500 chestnut trees grow on 60 acres near West Salem.

These trees are the descendants of those planted by Martin Hicks, an early settler in the area. In the late 1800s Hicks planted nine or so chestnuts, probably as a fencerow, or maybe as protection from harsh winter winds. Perhaps he was trying to bring a touch of the East to his new home in Wisconsin. You can be fairly certain that Hicks did not know he was planting history.

Planted outside the natural range of chestnut, these trees escaped the initial onslaught of chestnut blight, but in 1987, scientists found blight in the stand. Early efforts to save the trees involved the immediate removal and destruction of any tree suspected to have blight. The fungus prevailed and a team of scientists proposed a new tactic – inoculating the trees with a debilitated strain of the fungus that had its own disease – caused by a virus!

The largest remaining stand of chestnut has now become the largest laboratory in the fight against blight. Scientists who once marveled at the large size and beauty of the forest are now working shoulder to shoulder to try to save the trees and prove their theories at the same time.

Fueled by the shared will to bring American chestnut back to the Eastern forest and funded by the American Chestnut Foundation, the Wisconsin Department of Natural Resources, the USDA Forest Service, and the universities of West Virginia, Michigan State, and Cornell, this team is making a valiant effort to save the La Crosse County chestnuts.

Scientist and Plant Pathologist Jane Cummings Carlson of the Wisconsin Department of Natural Resources serves as guardian, local arrangements coordinator, and liaison to the landowners. For the past 15 years, Cummings Carlson has watched over the forest with the protective eye of a parent. She has consulted with the best pathologists in the country, written research proposals to gain funding and continues to be a stalwart champion for the chestnuts in La Crosse County.

Landowners Ron Bockenhauer, and Karl and Debbie Rhyme know the trees are special and lend their support by granting access to the scientists and allowing tours and field trips on their property.

When removing blighted trees no longer proved an effective solution, Cummings Carlson sought the guidance of Dr. MacDonald. He suggested using a naturally-occurring virus to attack the fungus that causes chestnut blight. The two contacted Dr. Dennis Fulbright at Michigan State University. Dr. Fulbright had been studying a stand of recovering chestnut in Michigan and had isolated a virus growing within the fungus, (termed a "hypovirus") that weakened the fungus sufficiently for the trees to recover. Although the hypovirus had been previously discovered in Europe, this was the first time it had been found growing naturally in the United States. MacDonald's theory was that by introducing the Michigan virus into the West Salem stand, the virus would attack the fungus and the trees would overcome the blight.

Exotic invasives
Saving chestnut is just one thing that DNR plant pathologist, Jane Cummings Carlson worries about. Increased global trade has increased the number of insects and diseases entering our country and affecting forest health in Wisconsin. Always on the alert for a possible threat to the trees and forests of Wisconsin, she is also keeping a watchful eye on other exotic diseases like butternut canker, white pine blister rust, oak wilt, sudden oak death and gypsy moth.

The scientists quickly consulted Dr. Michael Milgroom of Cornell University. Dr. Milgroom's expertise focuses on genetics and DNA fingerprinting of plant viruses. He tested samples of the chestnut blight fungus in La Crosse County and concluded, "Isolates of the pathogen revealed only one strain of the fungus was present in the stand. This lack of genetic diversity in the pathogen creates an ideal situation for introduction of one biocontrol agent." His conclusion gave the green light to the scientists – the hypovirus might work!

In a procedure that appears to be half science fiction and half outpatient surgery, the scientists set out to introduce the hypovirus into the chestnut blight. They collected the hypovirus from trees in Michigan. Back in their laboratories they created a slurry of fungus mixed with the virus.

Like a doctor inoculating a child with a vaccine, the scientists punched holes in infected trees' bark, injected the slurry, then "bandaged" over the holes with tape. In Michigan, the virus moves from tree to tree with the fungus. Every chestnut is infected with blight, but the virus keeps the blight in check and many of the trees eventually recover. The scientists hoped the same would happen in Wisconsin.

Will the blight end the chestnut? The farmers rather guess not. It keeps smoldering at the roots and sending up new shoots till another parasite shall come to end the blight. – Robert Frost

The treated chestnut responded immediately. Trees began to heal over their cankers. According to Dr. MacDonald, "It was very rewarding. Every tree with a canker had a great response." However, the Michigan virus proved to be too debilitating. The virus was so efficient at attacking the fungus that it prevented the fungus from moving from tree to tree. Only the treated trees were recovering.

In desperation in the late 1990s, the scientific team used an Italian hypovirus to treat infected trees. Again, the treated trees showed signs of recovery. However the fungus continues to spread through the stand at a rate much faster than the virus. In addition, Dr. Milgroom has now discovered several genetic variations of the chestnut blight fungus present in the stand, making a large-scale rescue of the stand improbable.

Will the stand survive? That depends on whether you are a pessimist or an optimist. "It also depends on what you consider success," says Dr. Fulbright. "Is success a breeding population of chestnut that can survive the blight or is success saving a few individuals from the blight?"

Because of these perspectives, scientific opinion regarding the future of the stand varies. It is a safe bet that 50 years from now chestnut will still be growing in La Crosse County, but all 2,500 trees may not survive. They may not be as grand or awesome as they are now, but some will endure. According to landowner Karl Rhyme, "The trees are quite unique, and we are all trying to do something about the blight. The scientists do their thing, but in the end, Mother Nature does her thing."

Using a hypovirus to attack chestnut blight is just one approach being tested to restore American chestnut. Another approach involves successive genetic crossing of the American chestnut with the Asian chestnut until the resulting tree retains 99 percent of the American chestnut characteristics and the genetic resistance of the Asian variety. The American Chestnut Foundation is essential to both efforts.

Founded in 1983, the American Chestnut Foundation is a nonprofit organization dedicated to restoring the chestnut to its former range. The Foundation exists almost solely on private donations and raises funds for its breeding program as well as other chestnut research. Membership has grown to over 5,000 and Honorary Board Directors include President Jimmy Carter and Nobel Peace Prize recipient Norman Borlaug.

The Foundation follows founding member Dr. Charles Burnham's recommendations for breeding a blight resistant American chestnut. Dr. Burnham, famous for his work intercrossing corn varieties, developed a new breeding plan for chestnut, correcting the mistakes of previous efforts. Although Burnham recently passed away, his work lives on in the work of Dr. Frederick Hebard at the Foundation's farm in Virginia.

Dr. Hebard claims he "got infected early" with the desire to develop a blight resistant chestnut and says, "I just didn't know this would be a lifetime endeavor." Although it has been almost 100 years since chestnut blight was discovered in the United States, within the next five years Dr. Hebard and his colleagues expect to test a breeding population of chestnut for both blight resistance and American characteristics. A century without chestnut may sound like a lot in human years, but it is only a moment in ecological time.

To visit the Wisconsin chestnuts
To find out more information about the American Chestnut Foundation, please contact the foundation by phone: (828)281-0047, by e-mail at: or visit The American Chestnut Foundation.

Gina Childs leads the Information Management group of the USDA Forest Service office in St. Paul, Minn.