THEGREENGROK

The Return of the American Chestnut


by Bill Chameides | April 21st, 2009
posted by Erica Rowell (Editor)

Permalink | 5 comments
The American chestnut's range stretched from Maine to Florida. A fungus, brought to the U.S. from Asia, spread rapidly and quickly wiped out this important native tree. Now scientists are trying to bring it back. (American Chestnut Foundation)
The American chestnut's range stretched from Maine to Florida. A fungus, brought to the U.S. from Asia, spread rapidly and quickly wiped out this important native tree. Now scientists are trying to bring it back. (American Chestnut Foundation)

In honor of this week’s Arbor Day, here is the hopeful story of the American chestnut.

A Look Back

The American chestnut is a majestic, towering hardwood that once graced the landscape of the eastern United States. Growing to heights of 150 feet, the tree is noted for its long, serrated leaves; catkin flowers; and of course the chestnut itself — ever-roasting by an open fire thanks to the indelible image created by Mel Torme and Robert Wells in their 1946 tune first and famously recorded by Nat King Cole.

According to the American Chestnut Foundation:

“The American chestnut tree reigned over 200 million acres of eastern woodlands from Maine to Florida, and from the Piedmont west to the Ohio Valley. … An estimated 4 billion American chestnuts, 1/4 of the hardwood tree population, grew within this range.

The American chestnut tree was an essential component of the entire eastern U.S. ecosystem. A late-flowering, reliable, and productive tree, unaffected by seasonal frosts, it was the single most important food source for a wide variety of wildlife from bears to birds. Rural communities depended upon the annual nut harvest as a cash crop to feed livestock. The chestnut lumber industry was a major sector of rural economies. Chestnut wood is straight-grained and easily worked, lightweight and highly rot-resistant, making it ideal for fence posts, railroad ties, barn beams and home construction, as well as for fine furniture and musical instruments.”

All that changed at the dawn of the 20th century. A fungus — the Chestnut blight — was inadvertently imported into the United States on imported wood probably from China or Japan. The American chestnut had no resistance to this exotic disease and by the 1950s, its entire population had virtually disappeared.

Bringing It Back

But all is not lost. With the leadership of groups like the American Chestnut Foundation, scientists appear to be on the brink of bringing the American chestnut back.

The trick has been to go back to the place from where the chestnut blight first came: Asia. It turns out both the Chinese chestnut and the Japanese chestnut are resistant to the fungus — they can become infected but do not succumb to it (read more about this here and here). Maybe you’re thinking, then why not just plant the Chinese chestnut in place of the American chestnut? The thing is, it would hardly replace the America chestnut. For one, the Chinese chestnut lacks the stature of the American form — growing to a maximum height of about 60 feet instead of 150 feet. More critical is the American chestnut’s intricate, complex relationship to our ecosystem. For hundreds on hundreds of years, countless species of birds, mammals, insects and other organisms as well as soils and water have interacted with American chestnuts, tying them and their genetic properties to the land they inhabit. So instead, scientists have been busy creating a new chestnut hybrid that has the character of the American chestnut but with the blight-resistant properties of the Chinese tree.

Not being a botanist, I don’t know all the details of the hybridization process, but I gather that it involves painstaking experimentation with grafts of the trees until the desired properties are developed. A complication is that it does not suffice to develop a single tree whose seeds are used to propagate the hybrid throughout the region because that would produce a population of trees without any genetic diversity and would therefore be highly susceptible to other diseases. So scientists have been working to develop several variants of the disease-resistant American chestnut hybrid for propagation.

After many years of work, the American Chestnut Foundation believes it has developed a new strain of the American chestnut that will survive and has slowly begun planting seeds. If successful, the American chestnut may once again reign in the forests of the eastern United States.

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5 Comments

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  1. Matt
    Apr 22, 2009

    I have read just a little about the American chestnut and have a quick question. I understand the American Chestnut Foundation has crossed the tree with a Chinese chestnut and then crossed the hybrid back with the original chestnut stock, trying to eliminate all characteristics of the chinese chestnut except resistance to the fungus. I have also heard of the Chestnut Cooperators’ Foundation, which seeks to cross American chestnut trees that have managed to survive the blight to create a resistant tree that is all-American (pardon the pun). Are than any advantages to one of these methods over the other? Thanks. I would love to see the American chestnut thrive again.

    • Fred Hebard
      Apr 23, 2009

      If everything works as hoped, backcrossing will yield more genetic diversity from the American side than crossing pure American chestnut trees, in the short term of the next 10 to 20 years. This is because fewer crosses and progeny are needed for backcrossing, and the American chestnut trees don’t need to have resistance. However, there will always be some fraction of Chinese chestnut remaining in the backcross trees. Testing will reveal whether the Chinese fraction has a negative impact on forest performance; it will be a matter of opinion whether or not the American chestnut has been adulterated by the remaining Chinese genes. Numerous questions remain unanswered about either procedure, enough that it may be wise to pursue both.

      • Ken Blenk
        May 29, 2009

        I have been growing American Chestnuts for many years. I am pleased to see Mr Hebard acknowledge the possibility that hybrids may have some unforseen problems in the American forests. It is good that there are efforts to maintain the original tree. The pool of remaining viable American chestnut trees is essential to bringing back the American Chestnut. It took millenia for this tree to establish itself….it may take a long time to bring it back in a natural way.

    • Brad Stanback
      Apr 23, 2009

      The American Chestnut Foundation (TACF) is implementing a backcross breeding program to capture as much genetic diversity as possible from the existing population of surviving American chestnuts. After the initial crosses to Chinese trees, the resistant portion of the offspring are successively backcrossed to many different American chestnuts. This program is repeated by local chapters of TACF throughout the native range of American chestnut to insure that the resulting trees are adapted to all the climatic conditions where chestnut once grew. The American Chestnut Cooperators’ Foundation is conducting a breeding program using only large surviving American chestnuts. This program is taking advantage of the finding that some American chestnuts appear to have a low level of blight resistance compared to the vast majority of blight-susceptible Americans. These trees still become infected with chestnut blight and are often quite deformed by it, but they nevertheless survive for many years as opposed to the 4 to 5 years that is common with most infected American chestnuts. It is hoped that by crossing these American trees with a low level of blight resistance, offspring will be produced that have a higher level of resistance. This is somewhat of a long shot, but it avoids the introduction of non-native genes into the species. The American chestnut has been through a genetic “bottle neck” as a result of the introduction of chestnut blight and the death of so much of the native population of chestnut. However, there are still millions of surviving American chestnut sprouts growing on the forest floor throughout the native range. The possibility of capturing more of this genetic heritage would seem to be an advantage of the backcross breeding program of TACF.

    • Tim
      Apr 23, 2009

      That question has created much debate and contraversy. The fact that the two groups are cooperating in restoring the American chestnut indicates that each one sees value in the other approach. Personally, I lean toward the TACF approach, simply because the resistance genes in question evolved to fight this species of blight and their approach is capable of restoring a much more extensive gene pool than represented by the few large survivors. It is important not to confuse resistance with vigor and overall competitiveness. The non-resistant American chestnuts are every bit as vigorous and competitive as the large survivors until they die from the blight. Also, there is some question regarding the source of the resistance genes in the large survivors. I think it would be safe to say that any large survivors over two or three hundred years old do not have any non-American genes confering resistance. But how many of them are there? There are other concepts of “purity” that lead some to object to the hybrid method. Some do not like the idea of “polluting” the pure American genetics by introduction of foreign genes. But consider the issue in human terms – if it were possible to eliminate sickle cell anemia by introducing a non-African gene into the chromosome, would this even be an issue? I believe that TACF and ACCF are obligated to determine whether the resistance genes from the two programs are additive, and if so, to incorporate both in the restoration population. Besides, the genetic engineering guys will probably leave us both behind like “Methusala’s Children”; and that’s another ball of wax for other purists to debate.

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