Group trying to restore chestnut trees

Thursday, July 1, 2010


Staff Writer

HUDSON – Until Bonnie McCarthy took a casual walk in the woods, nobody realized that Hudson is home to one of the rarest examples of a long-gone American giant.

“I found these odd-looking shells or seeds – I guess you call them seed pods – on the ground. I looked up, and there were some more hanging on the tree,” McCarthy recalled of that day in the woods near her Ridgecrest Drive home.

“I got a tree book and found it was an American chestnut tree, and learned how they had died out.”

Her interest was piqued, and then one day she heard a talk by Hudson resident Curtis Laffin about attempts to develop a strain of the American chestnut that could resist the blight that virtually exterminated the species almost a century ago.

In the talk, Laffin discussed rare “mother trees,” the American chestnut that lives long enough to produce seeds that are used in attempts to breed disease resistance.

“He said, ‘Unfortunately, I don’t know of any mother trees in Hudson,’ ” she said. “So I said, ‘I do!’ ”

That moment of serendipity eventually led to Laffin being 60 feet in the air – courtesy of a bucket truck from the Asplundh Tree Expert Co., organized through Public Service of New Hampshire – carefully tying paper bags around 100 female flowers on the chestnut tree to keep them from being pollinated by the wrong sort of pollen.

In the next week or two, when the flowers are at peak readiness, Laffin or another representative of the American Chestnut Foundation will go up in the air again, remove the bags, carefully cover each flower with pollen from crossbred chestnut trees that show signs of resistance to the blight, then cover the flowers again to protect them over the summer.

In the fall, they’ll return yet again to harvest the nuts, which grow inside a prickly green pod like a cross between a tennis ball and a sea urchin.

(The horse chestnut tree, which has a seed pod that’s even more prickly and spine-covered, is an unrelated species. It isn’t affected by the blight.)

Growing in Peterborough

In the spring, those nuts – as well as nuts collected from three other “mother trees” in New Hampshire, including one in a Milford subdivision – will be planted in a special orchard, probably in Peterborough, joining several hundred trees already growing in multigenerational rows.

These are great-grandchildren of crosses between sickly American chestnuts and healthy Chinese chestnuts, which are blight resistant; subsequent generations are crossed with American chestnuts in an attempt to create a tree that is 15/16ths American, yet still has Chinese resistance.

As they grow, they’ll be hit with deliberate inoculations of the chestnut blight fungus, which will kill at least seven out of every eight trees, and crossbred to produce new generations. Those generations will be weeded out with fungus and crossbred, and their nuts planted.

If all goes well, this process will produce a New Hampshire-specific American chestnut strain, able to stand the cold and the fungus that produces chestnut blight, and which will be ready for widespread planting in our forests – but not until the year 2022 at the earliest.

“To do this, you have to love the species, you have to love the promise of species restoration. … It’s not exactly a quick process,” said Grace Knight, of Vermont, head of the Vermont-New Hampshire chapter of the American Chestnut Foundation.

Once widespread, now gone

Many people know the story of the American elm tree, a glorious species that lined city streets around America until it was virtually wiped out in the early 20th century by Dutch elm disease, which came here from Europe.

Attempts to develop disease-resistant elms are well publicized, and the Keene-based Elm Research Institute plants hundreds of its cultivars around the Northeast.

But fewer know the similar story of the American chestnut, an equally important tree.

“It’s hard to get people to even think about it, it’s so far removed,” said Laffin, a retired Fish and Wildlife ranger who has been telling the story of the American Chestnut Foundation’s efforts. “If you’re younger than 60, you don’t even remember the chestnut.”

This is striking because the American chestnut was so valuable.

It formed as much as a quarter of the average hardwood forest throughout the eastern U.S., stretching from Mississippi to the edge of Maine.

Its fat-rich nuts fed wildlife, as well as people – “chestnuts roasting on an open fire” – while its wood was prized for being rot resistant, strong and light. For centuries, it was a bulwark of America’s forests and forestry industry.

Then the blight hit, arriving from Asia. A fungus carried from tree to tree by beetles creates cancers that eventually girdle infected trees, destroying the bark’s ability to carry nutrients and starving the tree. The disease spread like wildfire throughout the continent, and New Hampshire’s chestnuts were gone by the 1930s.

Actually, that isn’t quite true. The blight doesn’t affect roots, which can survive for decades. If these are exposed to sunlight, such as when trees near them are logged, these roots can send up shoots that live for a couple of years, perhaps getting as tall as a person, until the blight kills them.

“There are little American chestnuts all over Hudson, all over (New Hampshire),” Laffin said.

Every now and then, perhaps because little fungus happens to be nearby, those shoots get big enough to produce nuts, becoming the rare “mother tree” before finally succumbing to disease.

Few, however, get as big as Hudson’s.

Genetic diversity

Kendra Gurney, the northeast regional science coordinator for the American Chestnut Foundation, came down to Hudson for last week’s flower bagging.

Delighted as she was by the size of Hudson’s tree, a foot across at chest height and standing at least 60 feet high, she wasn’t optimistic about its future, pointing to bark riddled with cankers.

“Getting nutrients now is like sucking through a straw with a hole in it,” she said. “I’d be surprised if it hangs on more than a year or two.”

This adds to the urgency of the collection process. The American Chestnut Foundation is eager to collect nuts from as many trees as possible, from as many different parts of the chestnut’s historic range, to increase genetic diversity.

“Each state is developing its own resistant line from its own trees,” Gurney said.

This is a different approach than one being used in American elm programs, which create as many descendants as possible from a few naturally resistant trees carrying names like Liberty and Princeton. There are also separate attempts to genetically engineer resistant strains of both trees.

Spencer Brookes, of Wilton, is one who helps oversee New Hampshire’s main chestnut tree orchard in the state-owned Shieling Forest in Peterborough, a role that includes having to individually water 400 trees each week that doesn’t have at least an inch of rain.

“The U.S. Forest Service is very interested in this,” he said.

He noted that new threats to other forest species in the Northeast – notably the wooly adelgid that’s threatening hemlocks and the emerald ash borer threatening ash trees – makes it all the more important to bring back the American chestnut.

“They’re going to survive global warming because we’re at the northern end of the range,” Brookes said. “They’re really more of a Virginia tree. I feel they’ll spread very quickly once we get a resistant tree.”

The foundation thinks it needs six generations of backcrossbreeding before it’s confident enough to create a “seed orchard” of trees whose seeds will be planted in the wild.

The first Peterborough trees were planted in 2008, and since the final generation has to be about 6 years old to produce mature seeds, widespread dissemination of New Hampshire strains won’t happen until 2022 at the earliest.

“I’m doing this for my grandchildren,” Knight said.

David Brooks can be reached at 594-5831 or dbrooks@nashua

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