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Thursday
Jul252013

Bringing back the giants

The effort to restore the American chestnut tree to Maine's forest

 

By Joe Rankin

Forests for Maine’s Future writer

The crew moves across the field, setting fiberglass poles, threading on plastic insulators, and stringing thick Fencing the Winthrop seed orchard (Photo: The Rankin File)black and white polywire around an orchard of tiny trees growing in flesh-colored, perforated tubes. The electric fence is to stop whitetail deer from nibbling on the young trees. 

“We thought we could get by with deer repellents and luck, but we didn’t. All of our orchards have been nibbled,” said Eric Evans of Camden, the vice president and breeding coordinator of the Maine chapter of the American Chestnut Foundation.

The irony is that most of the trees in this three quarter-acre orchard -- and thousands more that will be planted in adjacent plots across this field in later years -- will die a young death, sacrificed as part of the greater effort to restore a species that was once the bulwark of the eastern forests.

The volunteers stringing polywire and putting in posts are engaged in a noble cause, a decades-long effort to restore the American chestnut tree as the glory of the eastern forests. “We’re trying to reverse the greatest single species ecological disaster in the history of this country,” said Evans, who has been involved in the Foundation’s Maine chapter for 15 years.

The American chestnut, Castanea dentata, once grew from Mississippi and Florida to Maine and Ontario. One out of every four trees in the Appalachian mountains was a chestnut, and estimates of their population ranged as high as four billion. The tree was fast growing and sprouted vigorously from stumps, helping keep the populations up. A valuable timber tree, its wood was rot-resistant, straight-grained and easily worked. It provided huge annual crops of tasty, nutritious nuts for humans and wildlife. As you would expect of such a valuable tree, settlers took it with them when they moved, planting it in Michigan and Wisconsin, Oregon and British Columbia.  

The chestnut was a presence in American culture. Remember the poem that started “under a spreading Ripening chestnuts (Photo: Maine Chapter TACF)chestnut tree the village smithy stands” by Longfellow? Undoubtedly you’ve sung about “chestnuts roasting on an open fire” at Christmastime.

Disaster struck around the turn of the last century. It came in the form of a fungus -- the chestnut blight, Chryphonectria parasitica -- imported with a shipment of Asian chestnut trees. The Chinese chestnut, Castanea mollissima, was resistant to the blight; the American chestnut highly vulnerable. The blight was first noticed at what was then called the Bronx Zoological Park, now the Bronx Zoo, in 1904.

The hot, humid summers of the east provided the perfect environment for the fungus to reproduce. Riding the winds, transported by animals and birds, it spread rapidly, up to 50 miles in a year, leaving behind a forest of girdled and dead giants. In a few decades it had wiped out some three billion trees. Because of its propensity for stump sprouting, the chestnut didn’t become extinct, but the sprouts rarely lived long before becoming reinfected with the blight. However, some isolated pockets of bigger trees lived; and in the midwest and on the west coast there were chestnut groves of sizable trees not reached by the blight.

Maine was at the outer edge of the American chestnut’s range. And that might help in efforts to bring the tree back, said Evans, who’s been working on the project for some 15 years. 

Historical range of the American chestnut (Graphic: TACF) “Maine has, overall, probably the most big mature American chestnuts of any the states,” Evans said taking a break from putting up electric fence. “Indiana is right up there. But when you get into the center of the range there are so many chestnuts re-sprouting there’s a lot of blight. Trees don’t get to be big. But in Maine these that have come in since the blight are much more isolated. A lot of them have grown up in the absence of blight. There are roughly a dozen places in Maine where there are chestnuts over 75 feet tall and a foot and a half to two feet dbh (diameter at breast height).” 

In 2012 what is believed to be the tallest American chestnut in the east was found in Hebron, an isolated giant 95 feet tall. The state’s champion American chestnut grows in Atkinson. It’s only 74 feet tall. But it has a trunk 111 inches around and a larger crown than the Hebron tree.

The American Chestnut Foundation was founded in 1983 by a group of plant scientists dedicated to bringing back the giant of the eastern forests. It has 16 chapters. The Maine chapter was founded in 1998 and the next year began instituting a backcross breeding program that aims to transfer the Chinese chestnut’s blight resistance to the American chestnut and restore the chestnut to the eastern forests.

The Foundation’s backcross breeding started with a a cross between Chinese chestnut and American chestnut trees, with subsequent generations mated to native American chestnut trees with the dual aims of retaining the blight resistance of the Chinese chestnut and maintaining all the other features of the American chestnut, including its height. While the Chinese chestnut is a short, spreading tree, the American chestnut grows straight up to 100 feet.

The Maine chapter began its efforts to breed blight resistant chestnuts by manually pollinating wild Maine chestnuts with pollen from selected second-back-cross hybrids sent from the TACF Research Farms in Meadowview, VaIt has since bred 40 “lines” of hybrid chestnuts through backcrossing with native Maine chestnut trees. Two years ago it began creating “seed orchards” where thousands of seeds will be planted over the next several years. So far the group has 12 backcross orchards in 9 towns, and 7 seed orchard sites in 5 towns.

In the Winthrop seed orchard being fenced on this hot July morning, 1,200 seeds were planted two months earlier. Another seed orchard just down the road that holds 3,600 seedlings will be fenced later today.

“The plan is to have 19 or 20 lines (at this site) and by lines we mean a different mother tree,” said Maine chapter board member Larry Totten. So far this year, he said, volunteers have planted 8,000 seeds in several orchards. Last year they planted 6,000. Those seeds represent the beginning of the fifth generation of the six-generation backcross breeding program. The goal is to plant 56,000 seeds in all.Sheltered seedling (Photo: The Rankin File)

The seed orchards will allow the chapter to select for the most blight resistant trees. When the trees get about as thick as a person’s finger, each will be innoculated with the chestnut blight through a wound made in the bark. Then it comes down to the survival of the fittest. The volunteers will select the two or three out of each plot of 150 that show the most blight resistance to harvest seeds from. The rest will be “rogued out” or culled, which is why this orchard plot of 1,200 trees will hold only a double handful of trees in a few years. The survivors will be the ones that produce seeds that, hopefully, will help return blight-resistant American chestnuts to Maine’s forests. 

Some of the delay in testing for blight resistance might be eliminated. Scientists have sequenced the Chinese chestnut genome and are now working on the American chestnut genome, said Evans. There’s a real possibility that in the near future DNA testing of a piece of a seedling’s leaf could reveal how blight resistant it Chestnut burs ready to go (Photo: Maine chapter TACF)is. Screening tiny potted seedlings could greatly reduce the number of trees that need to be planted in the seed orchards. 

Meanwhile, scientists at the State University of New York have taken a different angle, inserting a wheat gene into the American chestnut genome that provides blight resistance. Those could become the first genetically modified trees released into the forest.

In any case, bringing back a giant of the forest is a lot of work. It’s also expensive. Evans figures the Maine Chapter has spent $70,000 on its restoration work so far and could spend another $100,000. It cost about $500 just to run electric fencing around this  thee-quarter acre orchard. The chapter now has plans for eight fences in three towns, with the cost estimated at $8,000. The money comes mostly from dues or donations, he said, and the cost doesn’t include the thousands of hours of volunteer labor hand-pollinating trees, collecting nuts, planting nuts, laying down ground cloth and so on.

It’s also not a project for those who want instant results. It normally takes a chestnut tree seven years to bear Chestnut blight (Photo: Maine chapter TACF)nuts. So the trees planted in this Winthrop orchard -- or those left after their fellows are “rogued out” -- won’t begin bearing until 2019 or 2020. That’s the earliest Evans says the group would be able to release blight resistant Maine-grown chestnuts -- the sixth generation of the backcross breeding program. It might be later. All depends on how things go. “It will be a 10-15 year process to completely fill the seed orchards with all 40 breeding lines, evaluate, and rogue them,” said Evans. “I might call it the ‘home stretch’ 10 years from now when we are harvesting and test-planting seeds from the first several lines planted last and this year.” 

But even that’s not it. Having selected for blight resistance, it may be decades before anyone knows whether they’ve succeeded in their task to create a resistant American chestnut.Collecting burs (Photo: Maine chapter TACF)

“Probably not in my lifetime” seems to the common answer if you ask these volunteers, most in their sixties and seventies, when they’ll be able to pop the cork on the champagne and drink a toast to their work. Evans said he is “optimistic that 15 years from now we will be planting chestnuts that have blight-resistance good enough to compete and evolve in the Maine woods.”

Evans said he was always interested in trees. As a 16-year-old Boy Scout on a trip in the Blue Ridge Mountains he stumbled on a grove of standing dead chestnuts. Later, back at the cabin, he was able to figure out what they were through leaves on a stump sprout. Much, much later in life he came upon the work of the American Chestnut Foundation and founded the Maine chapter. He’s remained involved in the effort not so much because he wants to leave a legacy, though he acknowledges there may be a little of that, but to bring back something that is too good to lose. 

Totten’s introduction to chestnuts came some 10 years ago when he bought two trees from Fedco Trees and planted them at his place in West Bath. They lived three years, not succumbing to the blight, but probably to clay soil, said Totten. A friend gave him two more, which he planted at his camp in Jackman. They’re still growing strong and are about 12 feet tall. Totten said his wife gave him a copy of “Mighty Giants: An American Putting up deer fence around a Winthrop seed orchard. (Photo: The Rankin File)Chestnut Anthology” and he was drawn to the story of the tree and efforts to restore it. “Somebody’s got to do it,” he said.

Judy Stone is a fencing volunteer on this Saturday and a professor of biology at Waterville’s Colby College who teaches a popular course on forest ecology, including a section on the chestnut blight.

She said she was initially a little ambivalent about the idea of bringing back the species, thinking it smacked a little of hubris. But, as she learned more, “I became a convert,” she said. Stone said she’s impressed not just with the goal, but the high level of dedication and organization the ACF and its chapters evince. 

“I’ve done a lot of volunteer work. It’s very rare to see such a well organized volunteer effort. You think of the level of organization this requires. It’s complicated. It’s on a massive scale, on a continental scale, and these people are doing it,” Stone said. “To participate in something like this is epic. You’re making a difference that’s going to persist for eternity, essentially.”

Joe Rankin is a forestry writer, beekeeper and market gardener. He lives in New Sharon, where he has two American chestnuts growing in his backyard.