View Our Woods
See Us On:
« Planting yourself in the forest “Green” burials are a growing thing | Make a Home for Wildlife with the Help of Author Charles Fergus »
Thursday
Jun272019

The American elm: Past, present . . . future?

Years ago I planted an American elm in my yard. I was creating what my wife likes to call an arboretum on the handful of our 75 acres that weren’t already trees. I wanted an elm. It was one of the cultivars said to be resistant to the deadly Dutch elm disease. It’s now about 15 feet tall, though growing more slowly than I would like.

But a couple of years ago, as my forester and I were walking through the woods, I abruptly stopped and asked. “Hey, Daren, what is that tree over there?” It was big, but not easily identifiable. This was late winter. No leaves out. And anyway, there wasn’t a branch for a long way up. “I think it’s an elm,” he replied.

An elm. And a big one. Probably close to 100 feet tall. I couldn’t reach all the way around it. About 100 feet from a paved road, a couple of hundred yards from the elm I planted in memory of the elms of my childhood. I later found other specimens along the old roads. Elms weren’t just a memory.

Dutch elm disease was one of the great ecological disasters of the modern age. It wiped out elms by the millions, clearing them from city streets they had shaded for decades, and from forests across a good chunk of the continent.

But not all.

Elms are still out there, healthy or unhealthy, growing and dying. Maybe tested by the fungus of Dutch elm disease, maybe not. Like small bands of humans surviving after a science fiction apocalypse. And some of these elms may hold the key to bringing back Ulmus americana in a big way.

Elms are, or were, one of the most widely distributed tree species in North America at one time. “They weren’t super abundant. If you look at the pollen record, there’s not that much elm in it. It’s usually listed under ‘other species’ or something like that. If you look at witness tree records it’s usually listed with the ‘other trees,'” said Andrew Barton, a forest ecologist and professor of biology at the University of Maine at Farmington and author of the book The Changing Nature of the Maine Woods.

 

Where the American elm was a major forest ecosystem player was in floodplains of rivers, said Christian Marks of the University of Massachusetts at Amherst and a researcher for The Nature Conservancy who heads a long-term project to breed resistant elms. European settlers, taken by the tree’s classic-vase shape, adaptability and fast growth, later made the American elm the king of street trees in the New World.

Nobody in the 1800s saw what was coming.

Dutch elm disease is believed to have originated in Asia, where some species of elms show resistance to it.

By 1910 the disease had come to Europe. In 1928 it emigrated to North America, a stowaway in a shipment of veneer logs destined for an Ohio furniture factory. The disease spread, felling elms as efficiently as Paul Bunyan did pine and fir.

By then the American elm was a fixture in eastern towns and cities. Their graceful arching branches turned city streets into a cool, leafy bower. Many U.S. towns and cities, proud of these trees, took the nickname “Elm City.” Waterville, Maine, for one. Old photos of Silver Street show the classic elm scene:  big trees, arching limbs, old houses.

Such scenes exist only in photographs now. The New York Times, in a 1989 article, estimated that, of some 77 million elms in North America in 1930, more than three quarters were gone. If you are a baby boomer, you probably watched as the trees died and were cut down. It was a rolling, slow motion disaster.

Main Street Calais PostcardBut, as the elms I’ve found in my woods in Central Maine show, there are elms still out there. Big and small. There are stately elms in city parks, some kept alive by chemotherapy. Fungicide treatments, in other words. But some just lived on. Barton said that, a few years ago, he was walking around the 100-acre woodlot he and his wife Sarah Sloane own in Farmington when he ran into an elm. Not literally. But, still, a surprise. “It was a very large elm. It was the last thing I expected to find in the middle of the woods. And . . .” he says it again. “It was a really good sized elm, maybe two feet in diameter, maybe bigger.”

Such elms may have survived because they’re resistant to the fungus. Or perhaps they were so isolated that they were never attacked by the elm bark beetle that spreads the fungus.

Barton is intrigued by elms. A decade ago, he started what he calls an informal research-cum-art project. He drove down the highways and byways around Farmington, documenting elms living in yards and along roadsides, taking their portraits. He says he wants to go back and catch up on how they’ve been doing, taking followup photos or, noting the deaths of those that didn’t make it.

Most living elms are not giants, like the ones in parks, or even the ones Barton and I found. Elms get three or six or 10 inches in diameter, then get noticed by the bark beetle, which descends like an angel of death and  . . . they die. But frequently they’ve already produced seed, thus ensuring the presence of the species in the forest.

There are three known strains of the Dutch elm disease fungus, so-named because researchers in The Netherlands did pioneering work on the disease: Ophiostoma ulmi, O. himal-ulmi, and the most aggressive, O. novo-ulmi. They are primarily spread by a trio of elm bark beetles, including the native elm bark beetle, Hylurgopinus rufipes, the European elm bark beetle and the banded elm bark beetle.

The bark beetle feeds on the tree, injecting the fungus in the process. The tree counterattacks by plugging part of its vascular system with gum. The result is that the tree, its plumbing stoppered, starves itself of water and nutrients. The first sign is generally yellowed foliage in the canopy. Death is not instantaneous, but it doesn’t take long either.

It was perhaps a measure of how much elms were beloved that European researchers began working to breed DED resistant elms in the 1920s. The research focused mainly on crossing European elms with Asian species that showed some resistance, like the Siberian elm, the Chinese elm and the Japanese elm. That research continues.

Today a half dozen resistant American elm cultivars are available, the most well-known being Princeton and Valley Forge. Not one of these is immune to DED. They are resistant. Even resistant elms can be felled by the disease if, for instance, they are under other stress. Drought, say.Deerfield Elm, photo courtesy of Christian Marks

For the past 10 years Marks has been the lead scientist in The Nature Conservancy’s elm restoration project, working in partnership with the U.S. Forest Service’s Northern Research Station.

Marks’ TNC work focuses on using “survivor elms” to provide the genetic material rather than cross breeding with resistant species. This works as a way to keep the American elm a distinct species since other traits aren’t introduced along with the genes for resistance.

Marks said something like 1 in 10,000 American elms has some resistance to the deadly fungus. That resistance varies from “a little” to “a lot” with most somewhere in the middle. Kind of a classic bell curve, though one weighted toward the “little” end.

But how do you find those resistant trees?

While I’d like to think my big elm would be a contender, it probably wouldn’t. Marks, who personally leads the effort to suss out suitable trees, says he has some fairly straightforward criteria. Size is one. He’s looking for trees over three feet in diameter because they are so old that they were likely exposed to the disease at least once, if not several times. Also, whether they are thriving in an area where there are a lot of dead elms, which would be, pardon the pun, a dead giveaway that they’ve been exposed. Elms that are isolated in the middle of a forest or a field, at least 300 feet from other elms, or that are growing outside of prime elm habitat of rich bottomland soils, often attain a large size without ever being attacked by beetles and challenged by the disease. My elm, he said, may survive for decades.

Marks has concentrated on his search on the Connecticut River Valley, prime elm habitat.

Tip cuttings are taken from selected survivor elms by arborists clambering like monkeys high above the ground. Some are taken with flowers and their pollen is used to pollinate the flowers of resistant cultivars like Valley Forge; the seeds are then planted and grown out. Elms are easy to grow from seed, said Marks. Other tip cuttings are rooted, a time-consuming process that effectively creates a clone of the parent tree. Not every cutting roots successfully, though Marks’ program has had good luck with the technique.

Thousands of seedlings and cuttings have been produced and transplanted to trial plots. These elms will be tested for resistance by exposing them to the DED fungus.

The objective is to find another 25 to 35 resistant American elm genotypes. That’s the number Marks figures it will take to restore the species as a king of the floodplain ecosystem in eastern North America. The more genotypes researchers have the better the chance of success.

It is definitely a marathon effort that carries its own set of frustrations, including securing long-term funding and maintaining partnerships over the years and decades. “A team is much more likely to keep something going than an individual or a small group of people can,” said Marks.

Photo courtesy of Christian MarksOne possible game changer: new gene editing technology. Researchers working on creating an American chestnut tree that is resistant to chestnut blight have successfully used it. Whether regulators allow their creation to be released into the wild likely will have a big impact on whether scientists decide to use the technique on other tree species such as elm.

At the current rate, Marks predicts that well before the end of the century researchers will have their 25 to 35 resistant genotypes and be planting specimens not only along streets, in yards and in parks, but in natural habitats as well. They’ve already been doing some of that, of course. Interestingly, out in the wild, deer are as big a danger to elms as DED. At one time there weren’t so many deer. Now, if Marks and his team of volunteers and interns want to find out whether elms can compete in the wild they have to put up fence or the trees they’ve nurtured are likely to end up as fawn food. Ice is also a problem. Spring breakup on frozen rivers can scrape trees right off the face of the earth.

Creating a new elm is important for floodplain forests, and the birds, mammals and other creatures and plants that live in them, Marks said.

There are essentially three species of tree that survive and thrive in alluvial areas. The other two are ash and silver maple. Ash is under siege by the emerald ash borer. The niches left by the disappearance of elms and ash is being filled sometimes with invasives, like Japanese knotweed, known for taking over ground and holding it against all comers.

Floodplain forests thus affected are impoverished ecosystems, a shadow of their former selves, diminished in variety and in sheer size of trees. Knotweed is not the same thing as a 100-foot tall American elm. “The way I see it is that our forest, our trees, are shrinking, and in an era where people want to use trees to soak up carbon, big trees are critical," said Marks.

Marks thinks it is possible to bring back the elm, biologically it’s a matter of breeding resistant elms and flooding — pun intended — the floodplain forests with them so their resistant gene-carrying pollen swamps the pollen from non-resistant trees also growing there. It will take time, sure. But it’s possible.

The question is, in a world where attention spans are short and “progress” is measured in weeks or months, not by years and decades, do we have the will to hang in there for the long haul? Are bringing back the graceful elms of our childhood to the forests where they once grew worth it to us?

 

 

Joe Rankin writes on forests and forestry for websites and magazines. He, and his elms, live in Maine.