Taxonomy

Chestnuts belong to the genus Castanea, a member of the beech family, Fagaceae, along with beeches, chinkapins, oaks. There are about 8 species of chestnuts in the genus Castanea worldwide, with 3 of those occurring primarily in the Eastern United States and Southern Canada.

The American chestnut (Castanea dentata), the Allegheny chinquapin or dwarf chestnut (C. pumila), and the Ozark chinquapin (C. ozarkensis) are the three species indigenous to North America. Other species include the European chestnut (C. sativia) occurring from Southern Europe to the Asia Minor, the Chinese species (C. henryi, C. senguinii, and C. mollissima), and the Japanese or Korean chestnut (C. crenata).

Early Uses

Chestnut was a staple food and medicine for Native Americans as well as peoples in Europe and Asia.  Alexander the Great planted Chestnuts across part of Europe during political campaigns.  Overall evidence of cultivation dates earlier than 2000 BC.

Before the introduction of the potato from the new world in the 15^th century, the chestnut was a reliable source of carbohydrates.  Chestnut flour stored well.  In fact, so many common people relied on the chestnut for sustenance that European royalty declined their consumption, scoffing them as “food of the poor.”

Much of the world considers chestnuts a luxury food.  Every year, just before Thanksgiving, local farm stands and grocery stores display crates of fresh chestnuts.  Reading this, perhaps you can taste the subtle sweetness of  your family’s famous chestnut stuffing.  We are all familiar with the song… “roasting over an open fire”.  The roasted chestnut was so adored by Americans that it became one of the most recognizable symbols of old-time Christmas festivities (thanks to Robert Well’s and Melvin Torme’s 1945 jingle “The Christmas Song”).  Today, chestnuts are cultivated commercially across the temperate Northern Hemisphere.  Thanks to modern shipping technology, chestnuts are enjoyed by people all over the world.

The American Chestnut

American Chestnuts Were Large and Highly Valued

The most impressive of the North American Castanea species is the American chestnut. Its size was so huge, it was nicknamed the “redwood of the east”. They were the dominant species in the woodlands, and provided essential ecological functions such as food and habitat for thousands of species. It was estimated that before the 20^th century, over 25% of the trees in the Appalachian Mountains were American chestnut.

For millennia these massive trees provided food, medicine, and timber to Native Americans of Eastern North America.  Later, they did the same for  generations of European immigrants. A modern estimate, taking inflation into account, would put the 1920 chestnut lumber industry at half a billion dollars. Its strong heartwood provided perfect straight beams for houses, barns, and warehouses as well as furniture, flooring, ship piers, fence posts, telephone poles, and pulp.

In the 19^th century, the chestnut was referred to as “the perfect tree”.  Its wood was  “superior in quality to any found in Europe.” Its acidic bark was valued by the booming leather industry for tanning. Farmers and landowners in the East preferred forested land of chestnut for livestock forage, as pigs and sheep especially enjoy chestnuts. The ripening of the chestnuts each fall was perfectly timed for fattening animals for slaughter before winter.

The Chestnut Blight Fungus Found in 1904

A detrimental fungus, first observed by chief forester Hermann Merkel at the Bronx Zoo in 1904, was later identified by American mycologist William Murrill as Cryphonectria parasitica.  The fungus is referred to as the chestnut blight.

This blight, accidentally introduced on trees of Asian origin, would become the demise of one of America’s most valued trees. Due to their ideal orcharding size, Chinese and Japanese chestnuts had become popularized in the United States and Southern Europe for grafting and hybridizing in the late 19^th century. Unfortunately, somewhere in the thousands of shipments of imported trees, the blight came along and took hold in both North America and Europe.

At first, the origin of the blight was a mystery.  Then, plant explorer Frank Meyer discovered that the fungus occurred in China and Japan. Millions of years of co-existence with the blight afforded these Asian trees a natural resistance.   But its sudden introduction to a new continent meant that almost no American chestnuts had natural immunity; unfortunately, the same would be true for most European chestnuts as well.

Blight is Airborne

The blight established successfully in the new world because of the large population of potential hosts and a habitable climate similar to that of its native range of temperate Eastern Asia.  The spores of the fungus are airborne and spread easily by wind, on insects, and on birds. Its spread was rapid.  The gigantic chestnut canopies acted as huge nets for the airborne spores.

In Pennsylvania, the blight was first observed in Montgomery County in 1908 by the Forestry Commission, which reported it was isolated in the area. The Pennsylvania USDA scrambled for a solution in 1911 by proposing the Chestnut Tree Blight Commission. They had hoped to barricade the disease and prevent spread westward, since by this time it was already uncontrollable in the eastern half of the state.

The Commission deciding destroying trees just west of the Susquehanna River could prevent the spread further west, but by the time the efforts began it was too late.  The blight was already west of the river. However, hopes remained high in the scientific community, as many studying the disease believed there was a solution, but patience was necessary.

Even one prominent scientist involved, F.C. Stewart (New York) said “…other kinds of trees and plants have been threatened with destruction through disease…So far as known, no other plant has ever been exterminated by disease. It is unlikely that the chestnut will be exterminated.”

Demise of the American Chestnut

Four Billion Trees Lost in 40 Years

Unfortunately, the optimism of scientists dissolved with repeated failure to stop the blight’s spread.  By 1940, most of the estimated 4 billion American chestnut trees, from Maine to Florida, were gone. As these massive giants succumbed to the disease and fell, the appearance and ecology of Eastern North America’s forests changed forever.

Few people today have any memory of American chestnuts and have likely never eaten one. Even Wells and Torme, in their 20’s when they wrote their famous song in 1945, may not have had any memories of the American chestnut other than of its demise.  Mel Torme was born in Chicago in 1925.  Though not common in the Chicago area, the American chestnut was present in southern Illinois.  It probably made its way into the cities each year for the holiday market. I like to think part of his inspiration for the song was childhood memories of his parents roasting chestnuts every holiday season.

The American Chestnut is Critically Endangered, But Not Extinct

Many people today are under the impression that the American chestnut, Castanea dentata, is extinct.  Extinction is final, meaning there are no living individuals of the species left, such as  for example, the wooly mammoth. There are living American chestnuts, though they rarely (if ever) reach their former glory of 100-foot-tall-glory and 10-foot diameter trunks.

The IUNC (International Union for Conservation of Nature) Red List of Threatened Species (founded in 1964) is a comprehensive global inventory of the conservation status of living species.  It is considered the authoritative entity on species conservation.  There are precise criteria for evaluating the risk of extinction for living species of animals, plants, fungi, and other organisms.  Along with over 6,800 other species, the American chestnut is categorized as “critically endangered” — meaning it faces an extremely high risk of extinction in the wild.

Blight Stunts, But Does Not Immediately Kill the Chestnut

Interestingly, the blight does not kill the trees immediately, because it does not penetrate the crown and kill the roots of the tree. Many mature trees, with massive trunks, had their tops killed off by the blight but later continued pushing new sprouts from the crown, utilizing massive amounts of stored energy in the roots.

Usually, as these new shoots reach 10 to 15 feet tall, they show symptoms of the blight and deteriorate. They almost never bear fruit, partly because they are so jeopardized due to disease and depleted energy, but also because the forests have continued to grow around them and shade them out.  In their degraded state, the trees utilize energy reserves.  Without sufficient replacement from healthy photosynthesizing tissue,  the lingering crowns and roots eventually rot away.

Some Scientists Classify the American Chestnut as Functionally Extinct

Though not truly extinct, the jeopardized state of the remaining American chestnut has led many ecologists to recognize the species as “functionally extinct.” This is a term reserved for species that have too few individuals left to perform ecological roles and/or to sustain a long-term, viable population.

And the blight isn’t everything the chestnut is fighting!  Ink disease (Phytophthora cinnamomi) is a lesser known but equally destructive disease.  It made its way into the United States from Europe in the early 19^th century. Mature trees die quickly from root rot due to ink disease. It was most destructive in the South-eastern United States.  It affected American chestnuts and Ozark chinquapins as well as other native trees such as shortleaf pine (Pinus echinata) and Fraser fir (Abies fraseri). This disease, along with the chestnut blight, persists in American woodlands and continues to disrupt forest ecology by killing off important tree species, including surviving American chestnuts.

Restoration of the American Chestnut

Small Populations Remain

While there are not enough resistant trees to sustain a robust wild population, isolated populations of healthy American chestnuts have survived. There are a few locations in Northern Michigan with large, unaffected trees.   It is not known whether these were planted or occurred naturally, or a mix.  It is likely the latter, since Northern Michigan is slightly out of the former natural range of the American chestnut. Because of their isolated location, and distance from most other wild chestnuts, these trees were able to escape the blight…at least, for now.

There are also a few  isolated populations of American chestnuts in the East.  They are resistant to the blight most likely due to random, natural mutations.  In Pennsylvania, a handful of these resistant trees are scattered across the state.

There are some large orchards in the Pacific Northwest. Western settlers took chestnut seeds with them on their pilgrimages.  These trees and their progeny have survived in the region. The arid environment of the West Coast is un-inhabitable to the blight, so the trees have remained safe from infection. However, they are thousands of miles away from the ecosystem that desperately misses their presence. While these isolated populations may seem like a saving grace for the species, it may only be a matter of time before they, too, perish.  It is likely only their geographic isolation from the blight that has kept them safe. If and when the blight reaches them, they will succumb.

Is There Hope?

 

Hybridization

The American Chestnut Foundation (TACF) was founded in 1983.   They have been hybridization, and how the infusion of resistance genes from the Asian species could save the American chestnut.

TACF uses an approach they call 3BUR: Breeding, Biotechnology, Biocontrol United for Restoration.   They began by crossing Chinese chestnut trees, which are naturally resistant to the blight, with their American cousins. The result was trees that were 50% American, 50% Chinese. They back-crossed these 50/50 trees to the American species, resulting in trees which were 75% American. They repeated this procedure and produced an American chestnut tree with no Chinese characteristics other than blight resistance.

After four generations of breeding, they have a population of American-Chinese-chestnut hybrids, which carry blight-resistance from the Chinese chestnut (C. mollissima), but most of their genetics from their American backcrosses.

Since the trees are wind pollinated, cross pollination between pure American chestnuts and Chinese chestnuts– hybridization – can occur readily in nature.  The differences in outward appearance between a true American chestnut and a wild hybrid can be minute.

With the infusion of genetics from the Asian species, it is a concern to some that the already jeopardized genetic diversity of the American chestnut will become contaminated.  If one day the American chestnut is completely replaced by hybrids, the original species essentially would be “extinct” and replaced by a genetically new species. Every American chestnut alive today, even if stricken with blight, is a valuable piece of the American chestnut gene pool.

CRISPR

Scientists at the State University of New York made an incredible discovery which may hold a new answer for saving the American chestnut. They discovered a gene in wheat that produces oxalate oxidase, an enzyme that enhances blight tolerance. TACF is now investigating CRISPR and other gene-editing processes. Using CRISPR, scientists can insert this gene from wheat into the genome of the American chestnut. The American chestnut then could be blight resistant with incredible accuracy. The efforts are strictly for restoration, and not for commercial production.  (They do not plan to patent any edited genomes.)

Biological Control of the Blight

TACF is also experimenting with natural biological controls. One method, hypovirulence, involves releasing a virus that would weaken the blight. This virus, combined with the natural defenses of the trees, could help prevent or stop infection before the tree dies.

Biological controls are common in the horticultural and agricultural industries.  By using one organism to combat another, the need for chemical pest controls can be reduced.  In many instances biological controls are very effective.

Many people have concerns over new advances like transgenics.  Others worry that using biological controls in the natural environment may have unknown hazards to other organisms.

Gene editing and biological control organisms, despite the concerns, are incredible options.  They are rigorously tested for environmental and human safety. In a situation so bleak, it is uplifting to see so many options presented for potential restoration.

The American Chestnut at Edge of the Woods…and Your Garden!

The American Chestnut Foundation has planted numerous orchards. The organization has 16 chapters across 4 regions in the Eastern United States, partnered with state universities including Penn State. At Edge of the Woods, we are happy to have one of these orchards on the nursery grounds, planted with the help of volunteers in 2012.

The orchard is comprised of approximately 80 wild, pure American chestnuts. The seedlings planted were from parent trees that were somewhat resistant to the blight. We have numbered each tree with a specific code that indicates its parentage and ecotype.

Over the first several years, the trees grew fast and seemed healthy.  Now, chestnut blight is infecting many of the trees.  Others are showing little to no signs of infection.  Some bear fruit and so tall they are hard to measure!

All the trees in our orchard came from a seemingly resistant parent, but many apparently did not inherit the resistance gene.  Each tree in the orchard has a unique combination of genetic material, so we let them live even as they decline.  They are part of a depleted gene pool and could hold other valuable genetics yet to be known. So, best they hang around as long as possible!

American Chestnut Seedlings

Because some of our trees are fruitful, we can propagate these chestnuts and sell them at the nursery. It is important that customers understand there is no guarantee that these trees will not fall victim to the chestnut blight. In fact, the chances of them surviving long term are rather slim — but not impossible!

At worst, the trees will grow 10 to 15 feet tall and appear healthy for the first 6 to 10 years.  Then they may show symptoms of infection and die back.  When they do, either remove them or allow them to continue to re-sprout until they die.  Even as a multi-stemmed shrub, an American chestnut can still fulfil some ecological functions.  They provide larval food to approximately 125 species of moths and butterflies.  Many small mammals eat the nuts. Birds will use the tree for nesting.

At best, your tree will survive and grow into a tall stately tree. Because of the chestnut’s wind-propelled pollination, it is difficult to ensure pure pollination, as any nearby chestnut trees could cross-pollinate.

That said, we cannot guarantee purity.  But, given the planting density of American chestnuts in our orchard, we assume most pollination occurs between trees in the orchard, rather than from a chance Chinese or Asian chestnut further afield.

Why Plant an American Chestnut?

Plant an American chestnut is to honor the memory of a once magnificent species, and as a reminder of society’s  ignorance of that which we do not understand or consider.

The chestnut blight, ink disease, wooly adelgid (Adelges tsugae), emerald ash borer (Agrilus planipennis), and butternut cankers (Sirococcus clavigignenti-juglandacearum and Melanconis juglandis) were all introduced into our ecosystem accidentaly.

The American chestnut moth (Ectoedemia castaneae) and other insect species went extinct after the decimation of their primary host, the American chestnut.  Some scientists even link the extinction of the passenger pigeon (Ectopistes migratorius) to the disappearance of the American chestnut.  Losing their prominent food source may have been the final nail in the coffin for the already over-exploited species.

The American chestnut’s demise is sad.  We should remember it, though, for generations to come. In a world of growing global trade and commerce, the risk of accidentally introducing new pests is ever increasing.

The Spotted Lanternfly is one of the newest of these accidental introductions.  Concerns are growing about its potential for harming native plants and competing with native insects, as well as its detrimental effects on agricultural crops.

We won’t be using American chestnut timber for building foundations anytime soon.  Nevertheless,  its story is the foundation for modern knowledge on the power of introduced pest and the importance of risk evaluation.

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To learn even more about the American chestnut and efforts to restore it, visit https://patacf.org/.