Connecticut's beech trees

It's a sunny day in October, and Michael Klimaszewski is zipping along in a golf cart on the 458-acre Choate Rosemary Hall campus in Wallingford. The school’s arborist for four decades, the genial, bearded sixty-something-year-old comes to a stop in the northeast quadrant of campus and steps out. To his right, across an expanse of lawn, is an award-winning pin oak that has been recognized as one of the finest in the state. He’s proud of that one (he has the plaque in his office), but he feels connected to all the trees in his care, here and at home, where he has a small orchard in his backyard.

“I have a love for trees. I swear, they talk to me sometimes,” he says as he touches the boughs of the tree to his left.

Choate Rosemary Hall's "Elephant Tree."

Choate Rosemary Hall's "Elephant Tree."

It’s a monolithic 95-foot-tall European beech. Known as the “Elephant Tree” to generations of children in the community, it has a massive trunk of smooth, gray bark—over five feet in diameter — that rises like an enormous pole for this tall tent-of-a-tree. When the tree’s swooping branches are fully leafed out, the ground-brushing boughs make tent flaps that invite children — and adults — to pass through. Inside is a 700-square-foot, round “room” that feels like it might belong to Tolkien’s Middle-earth.

Estimated to be 245 years old, this venerable giant of the “cut leaf” variety was likely sprouting right around the time the Constitution of the United States was being ratified. But today its fate is uncertain. That’s because in the spring of 2023, Klimaszewski recognized some telltale signs: a canopy that didn’t seem to be filling out as much as in years past, and leaves that were abnormally curling. The Elephant Tree was suffering from beech leaf disease.

First observed in this country 12 years ago, beech leaf disease (BLD) is now attacking millions of trees in about a dozen states. The disease imposes a high mortality rate on beech saplings and young trees, and its devastating effects are putting mature beech trees into decline. Many of them will die several years after infection.

That’s a gut-punch to Connecticut, as the American beech is the third most abundant tree species in our forests, and it plays a pivotal role in whether or not those ecosystems thrive. Not to mention that many stately European and Japanese subspecies, which are also susceptible to BLD, beautify our backyards, school campuses and urban settings like Hartford’s Elizabeth Park. The total number of beech trees in Connecticut is estimated to be 57 million.

Twenty years ago there was no such thing — as far as any American forest pathologist knew — as beech leaf disease. But now, in our lifetimes, we can expect a wide-scale transformation of our state’s forest composition, a massive shakeup of natural habitats, and the potential loss of centuries-old giants like Choate’s Elephant Tree.

How did this happen? What can we do about it? And what does this existential threat to our beeches teach us about the historical, ecological and personal value of trees?

A new pathogen emerges

In 2012 a biologist working for a local parks system in Ohio noticed a strange phenomenon. Some American beech trees there had disease symptoms he’d never seen before: dark interveinal bands making diagonal stripes on the leaves, as well as bulging malformations. Soon more and more trees were not just afflicted, they were dying. Various specialists—plant pathologists, entomologists, mycologists—were consulted, but in the ensuing five years no causal agent was identified. The plague continued to spread regionally, and the scientific mystery remained unsolved.

The lucky break came in 2017. A plant pathologist who was examining some affected leaves with the aid of a microscope discovered the confounding presence of nematodes. Although these miniscule roundworms are commonly found in fleshy plants, ornamental flowers and garden staples such as hosta, it was unheard of for them to be feeding on trees. Scientists scrambled to make sense of it, and unlikely partnerships began to emerge. Forest pathologists who had negligible working experience with nematodes joined forces with nematologists with zero experience in forestry, along with scientists from the USDA and the US Forest Service, to create a working group dedicated to unraveling the mysteries and mechanisms of BLD.

Dr. Robert Marra, a forest pathologist with the Connecticut Agricultural Experiment Station in New Haven, was one of the early members of the group. He says it was difficult at first for many to believe these particular parasites were causing the demise of beech trees. Fungi, parasitic insects—these are types of organisms that forest pathologists are trained on. Not nematodes.

“We’ve never had a foliar nematode on trees before,” he says. “Ever, anywhere.”

While their host choice was unprecedented, the parasites were found to be behaving in textbook fashion, that is, hacking into and harnessing the host’s cell machinery to create ideal feeding sites. Undetectable to the human eye, nematodes will attach themselves to cells within the leaf’s inner tissues. There they will emit effector molecules that stimulate the cells to multiply and become enlarged. Using a body part called a stylet — sharp and hollow like a hypodermic needle — nematodes then puncture these cells and suck the precious juices out.

During the summer months, nematode-infested leaves interfere with the trees’ capacity for photosynthesis. But the greatest harm is inflicted later, in the fall and winter. That’s when nematodes make their way to the branches and enter the buds—the places from which new leaves will be created in the spring. Their feeding and reproductive activity in the buds is the reason that symptomatic leaves—marked by dark bands and malformations—emerge in the spring. Eventually, in subsequent seasons, damaged buds cease to produce leaves at all. The result is beech trees with once thick, leafy, dominant canopies now bare except for a scattering of raggedy leaves.

In a last-ditch effort to fulfill their energy needs, trees will sometimes put out second-flush leaves from as yet unaffected buds. But these pale, flimsy suncatchers — looking like hurried sketches of the idea of beech leaf — are not enough to compensate. Unable to sufficiently feed themselves through photosynthesis, the trees begin to starve. The tree tips that should be growing up and out begin to shrink and die, both above and below the ground. This process is known as tip dieback.

“Tip dieback leads to branch dieback, which results in a crown that is smaller than the root system was originally sized to support,” Marra explains. “So you get tip dieback in the roots as well.”

A devastating impact

How many trees in Connecticut will die from BLD? Tens of thousands? Millions? The US Forest Service reports that: “Beech tree saplings infected with BLD usually die within five years of infection. Mature trees tend to take several years to die of the infection.”

But Marra says that, technically, mortality can be difficult to characterize. Trees will certainly die, but there’s also the possibility that some beeches in Connecticut’s forests might end up only mostly dead, or moribund. This would be when, over time, the portion of a tree that lives above the ground dies, but some life remains in the roots, which may continue, in Sisyphean futility, to throw up new shoots that will never grow into mature trees capable of reproduction. Either type of death will drastically change the composition of the forest.

And there is no doubt that the large-scale loss of fruit-bearing beech trees in our forests will profoundly affect the ecosystems where they live. In more than a dozen types of forests, beech trees are considered a foundation species, meaning they are of supreme ecological importance.

In a 2019 paper published in the journal iScience, Harvard University ecologist Aaron Ellison stated, “Foundation species define ecosystems, control the biological diversity of associated species, modulate critical ecosystem processes, and often have important cultural values and resonance.”

Beech trees support a tremendous amount of life in the forest. They are central to a food web that encompasses at least 100 different species. In the category of insects, these include the beech leaf-tier and about two dozen other moth caterpillars; the beech girdler and about 20 other wood-boring beetle larvae; and several types of aphids, leafhoppers and plant bugs. Since most insects are specialists who favor, or are exclusive to, one species of tree, the loss of a significant number of beeches will decimate these insect populations.

And the insects sustain the birds.

Both nesting and migratory birds rely on beech-hosted bugs for food. Wood thrush, scarlet tanager, and black capped chickadees are among the species that prefer to nest in beech hollows, where their food source is both plentiful and in proximity. What will these birds eat when insect populations disappear?

Meanwhile a handful of birds and several mammals of different sizes rely on beechnuts — rich in fats and protein — for their sustenance. These include white-tailed deer, black bears, wild pigs, squirrels, chipmunks and mice.

When beech trees die, other tree species such as black birch will likely take their place. But birch trees don’t produce hard-mast fruits, so there will simply be less food available in the forests.

Nature writers have rhapsodized about the very specific way that beech leaves filter light to the forest floor. Aesthetics aside, any change in the beech’s leafy umbrella will have a huge impact on the flora and fungi of the forest understory.

“[Beeches] have a very thick, dense canopy, so the soil temps are going to go up, the microorganisms are going to shift,” says Heather Dionne, a tree expert and former urban forester for the city of Hartford. “There’s so many repercussions.”

Among the plants affected will be herbs such as witch hazel and spring ephemerals like common trillium. These are species that flower early in the season, before beeches leaf out, when direct sunlight is plentiful. In summer they thrive in the soft beech-created shade.

Epifagus virginiana, commonly known as the beechdrop, is a wildflower that does not possess the cellular machinery to conduct photosynthesis and relies exclusively on beech tree roots for sustenance. Like many of the insect types, the plant is co-adapted and cannot simply move to another species of tree.

Invasive species are notorious opportunists, and when the beech’s influence on the understory is disrupted, the chances are that non-native plants will move in and take over.

“When you lose one tree species in a forest, you really throw off so many things about the forest ecosystem dynamics,” says Marra.

This beech forest near the Choate Rosemary Hall cross country trail in Wallingford—shown here in late summer 2023—used to be shady with a dense canopy. But now leaves are sparse.

The cost for humans

Losing beech trees in developed areas will affect not only local wildlife but also people. In Connecticut’s urban settings every tree counts toward removing pollutants from the air, soaking up runoff that would otherwise flood city streets, and providing cooling shade during ever-more-frequent heat waves, thereby improving the quality of life for people who live and work in the city.

Hartford’s entire canopy of 23,395 inventoried trees can be appreciated via a software called TreeKeeper. The web-based tool enables users to search for trees by species and location. Green dots then appear on the map to show where trees are, and clicking on them elicits a pop-up window giving particulars of the tree or trees at that site.

Meanwhile, a side panel crunches some serious numbers related to the benefits of trees. Put together, all of Hartford’s trees are estimated to have a five-year ecological value of $680,933.

That number is based on such factors as carbon dioxide uptake, storm water mitigation and air pollution removal. In a hypothetical five-year period, Hartford’s trees will have sequestered the CO₂ equivalent of more than 10 million pounds of greenhouse gases. In that same period more than 19.4 million gallons of runoff will have been avoided. The amount of carbon monoxide, nitrogen dioxide, other pollutants and fine particulate matter filtered by these trees is in the neighborhood of 1.4 million ounces.

Neither science nor software has yet been able to put a dollar value on the feeling of sanctuary upon stepping into a tree’s shade on a hot summer day. Escaping the sun's burning rays causes immeasurable relief.

The benefits of trees — both calculable and intangible — are what Heather Dionne was talking about on a podcast episode produced by Hartford’s Department of Public Works in 2022.

Asked what her message would be if she could put anything on a billboard, she responded, “Trees are life.”

Trees are also history.

Hartford, perhaps more than any other American city, knows the incalculable value of a single tree. After all, this is the city of the Charter Oak. It was thought to be a thousand years old when Captain Joseph Wadsworth hid in its hollow the colony’s Charter of 1662, which England had revoked and wished to physically retrieve in 1687. Loved and venerated in life, the Charter Oak was mourned in 1856 when it was toppled by a violent summer storm. The city held a funeral and a parade for it, and any piece of it or artifact made from it was revered as a precious relic. Its acorns were planted across the state giving rise to its “scions,” which number about 100. The tree was also commemorated by a coin and a postage stamp before it became an official symbol of the state.

There is, of course, no tree today that is comparable to the Charter Oak. But Hartford’s inventoried trees do include just over 200 beeches, now threatened by BLD, and many are highly visible in the city’s most cherished green spaces.

Among them are a number of venerable European beeches that bring beauty to Bushnell and Elizabeth parks. Dozens of mature American beeches proffer shade in the wooded areas of Keney Park and several of them decorate the picturesque property of the historic Mark Twain House. It’s difficult to imagine how changed this city would be if it were to lose any of those trees.

One of Bushnell Park’s stately European beech trees, on the Elm Street side, is listed on the TreeKeeper map as Site 36451. It has a DBH (diameter at breast height) of 42 inches. Arborist math (multiplying the DBH by the established growth rate for the species) would indicate an estimated age of 168 years. Meaning that somewhere around 1856—the very year Hartford’s most famous oak crashed to the ground—this beech came to life to carry on the legacy of the city’s magnificent trees.

Will this and Hartford’s other beeches still be here 20 years from now? No one knows.

How did this happen?

Once American scientists realized that a foliar nematode was implicated in BLD, they started analyzing morphological data to identify it. That and DNA sequencing led them to the conclusion that it rightly belonged in the genus Litylenchus. The kicker? No nematode in that genus had ever been documented in the western hemisphere. So what was this new parasite doing here, and why were beeches its preferred host?

Unbeknownst to them, across the globe was a Japanese nematologist who’d known about this nematode since 2004. While walking in the forest one day he happened to notice some strange-looking leaves on a type of native beech called Fagus crenata. He determined that the causal agent was a previously unidentified nematode. Of the estimated one million species of nematodes in the world, about 24,000 are known and named. Like so many others, this one was doing nothing more than stealing some of the resources of the host plant like an annoying moocher. Its effect on Japanese beech trees was negligible.

This was boring, back-burner stuff, and it wasn’t until 2019 that Japanese scientists finally got around to publishing it. Their paper, appearing in an international nematology journal, officially named and established this new species as Litylenchus crenatae.

By that time nematologists in places as far away as New Zealand were helping American scientists to connect the dots. The American subspecies has since been christened Litylenchus crenatae mccannii, after David McCann, the plant pathologist who first saw it under the microscope.

Polarized light microscopy of live *Litylenchus crenatae mccannii*. (a) female; (b) male; (c) eggs; (d) juvenile. Carta et al. 2020. *Forest Pathology,* Vol. 50, No. 2

Polarized light microscopy of live *Litylenchus crenatae mccannii*. (a) female; (b) male; (c) eggs; (d) juvenile. Carta et al. 2020. *Forest Pathology,* Vol. 50, No. 2

As is the case with other invasive species, this parasite appears to have co-evolved with the trees in its native habitat. That is why the beeches of Japan are weathering its attack just fine: They have developed some kind of protective qualities or mechanisms that beech trees elsewhere don’t have.

But how did L. crenatae get here? Did it stow away on a cargo ship that came into port on the Great Lakes, explaining why that region was the first affected? Did it hitch a ride on an imported ornamental tree species?

That mystery remains unsolved.

However, scientists have a pretty good theory of how the parasite has spread locally and regionally. Such a tiny invisible worm on the surface of a leaf could easily get stuck in the feather of a bird, the fur of a squirrel or on the leg of a beetle and be transported to another tree.

“We figure they move on anything and everything,” says Marra.

He also notes that nematodes can dry up and travel on the wind like pollen, only to be rehydrated and revived elsewhere.

A hypothesis currently being tested is that wet events increase the likelihood of spreading. In the same way that earthworms are stimulated to come out of the ground when it rains, nematodes start moving when there’s water on the surface of the leaf they’re feeding in. Rain causes stomates — the pores through which leaves “breathe” — to open up, providing a quick egress for the tens—sometimes hundreds—of thousands of nematodes crammed inside the leaf.

“It’s like opening the doors of a subway car,” says Marra. “If people are packed together against the door, they almost spill out.”

Once they are on the surface of the leaf wriggling around, the chances are good of getting picked up by an unsuspecting bird or bug.

Whatever the vector or vectors, the nematodes have caused BLD to spread from Ohio to the East Coast, prompting an alarmed US Forest Service in 2020 to consider it a national threat and to implement its “enhanced monitoring” protocol to engage cooperators in every state.

Connecticut was the first New England state to be affected, when in 2019 symptomatic trees were observed in Fairfield County. By 2022, BLD was confirmed in every county of Connecticut and Massachusetts and in portions of New Hampshire and Maine. So extensive and demoralizing was the spread that year that Marra still refers to it as “The BLD Hellscape of 2022.”

This map of the progression of beech leaf disease was produced by the USDA Forest Service and Cleveland Metroparks.

What can be done?

In the 2015 movie "The Martian," based on the book by Andy Weir, a stranded astronaut played by Matt Damon must figure out how to grow enough food on Mars to feed himself in the several hundred days before he can be rescued. He starts calculating such things as the caloric value per potato and how to alter the composition of the red planet’s soil to accommodate such a crop. In a video diary entry he declares, “In the face of overwhelming odds, I’m going to have to science the shit out of this.”

In the 12 years since beech leaf disease appeared in this country, a great deal of science has been applied in an effort to stop the overwhelming and disheartening infestation of BLD. Members of the BLD working group, who meet monthly by Zoom, have surveyed thousands of acres of forest. They and their partners have established more than 100 monitoring plots, including 11 spread across Connecticut, where annual data on crown density, tip dieback, and more is collected. They’re also looking at population genetics and whether nematodes in a particular area are reproducing sexually or via parthenogenesis—that’s when females lay eggs that are basically their clones.

Marra and three other colleagues will go to Japan this fall to learn more about the genetics of nematode populations there to better understand the origin of the ones in the US. They may also be able to gain insight into what specifically about the Japanese beech, F. crenata, confers protection against the parasites.

One of the major challenges is that a beech takes 40 years to become a mature tree capable of reproduction. It’s not possible to speed things up to find out whether different treatments, protocols or genetic modifications will result in beeches whose progeny is resistant to this particular pathogen. By the time we have enough data to create a rescue plan for Connecticut’s beeches, it will probably already be too late.

“Trees exist in decades,” notes Marra. "We don’t just grow beeches in the greenhouse like broccoli or lettuce.”

What does science have to offer?

At the moment only some existing agricultural products that can be applied in a sort of off-label use. Some arborists are spraying these pesticides or fungicides on trees to kill off nematodes in the leaves. But there is concern that the pests will become resistant to this treatment, that these chemicals could have detrimental effects on the ecology of nearby streams and rivers, and that killing nematodes in leaves doesn’t necessarily eliminate the most harmful ones embedded in the buds.

The most promising intervention for BLD, one recommended by Connecticut’s DEEP, is a kind of potassium phosphite or polyphosphite fertilizer. This ground-soaking treatment, applied to the base of a tree a couple of times a year, does seem to curtail the nematodes’ ability to do damage to leaf buds. It was first tried in 2013 in Ohio, and over several years treated trees were documented to be healthier than untreated controls. Like some kind of super vitamin, the solution seems to invigorate the trees’ defenses.

Many urban foresters, including in Hartford, have already begun applying it to their most valued trees. Tree care companies, like the one Heather Dionne currently works for, also get requests from beech owners in the suburbs who are seeking the treatment.

Wherever they are, tree stewards will have to make decisions about which trees are worth saving and how much they are willing to spend.

Jack Schneider can’t really put a price on history. That’s why he is making a heroic effort to preserve the rare maritime beech habitats on Fishers Island, that nine-mile-long sliver of New York located about two miles off of Groton Point. Schneider is the steward of the Henry L. Ferguson Museum’s land trust, which owns three of the island’s five beech groves. Planted on what was originally pastureland, the beech trees on Fishers Island are about 100 years old and iconic. Schneider is loath to imagine a Fishers Island without them.

He says, “It’s almost a heritage issue—to keep the aesthetics for future generations.”

He first observed BLD symptoms on the island in 2021 and began treatments the following year. The topography of the place presents some challenges. Schneider’s system involves placing a 35-gallon vat for mixing the fertilizer and water at a higher elevation, running hoses downhill and using a measuring cup to apply the right dosage at each tree’s base. The recommended protocol is to apply it in May when leaves are most abundant, then again in June or early July.

Jack Schneider, steward of the Henry L. Ferguson Museum’s land trust on Fishers Island, applies a ground-soaking treatment. Photo by Kate Stevens

Jack Schneider, steward of the Henry L. Ferguson Museum’s land trust on Fishers Island, applies a ground-soaking treatment. Photo by Kate Stevens

He’s treating about 200 trees in total, a job that costs $1,500 for the product annually, plus $600 for the equipment and 150 hours of labor. A conservationist, not a scientist, he doesn’t have a control for this experiment. He just wants to save all of these trees, and he’s giving them supplemental water as well to help them weather the stresses of both parasitic infection and climate change.

This past March Schneider joined Marra for a workshop at the annual conference of the Connecticut Land Conservation Council. Marra is developing a pilot program through which volunteers associated with the state’s many land trusts and conservation areas can learn to do what Schneider is doing on Fishers Island.

Many of these entities won’t have the manpower or resources to treat more than a small number of trees in their land trusts. But keeping alive even five or 10 trees in a few dozen locations across the state would go a long way toward preserving the genotypic diversity of Connecticut’s beeches. Beech trees that are unrelated to each other have different genetic variations. Perhaps some will turn out to be more resistant to this parasite than others. The project would be like a seed bank, keeping some minor differences in the genotype from going extinct.

While the phosphite treatment provides hope for individual trees, this kind of intervention cannot be scaled up to address the beeches in acres and acres of state forests. What would such a thing cost? How could it be executed? Not to mention that messing with ecosystems is unwise.

As Marra notes, chemical control is not in the forestry toolbox.

“We’re not going to save thousands of acres of beech forest,” he says. “This is the most we can do right now.”

Hoping against hope

Seated at a long conference table in the Facilities Department office at Choate Rosemary Hall, Michael Klimaszewski looks over his tree master plan. It is a large satellite map of the campus, with green circles of various sizes representing trees and their relative sizes. He points to a small number of them that are marked with a red circle with an X through it. Those are the trees scheduled to be removed in the next year or so, either for disease or campus betterment. Klimaszewski hopes against hope that the Elephant Tree will never be marked as such.

Which is why he has a new BLD line item in his budget. He's willing to spend thousands of dollars for twice per year treatments for the Elephant Tree and handful of other prized European beech trees on the campus. To Klimaszewski, it’s a worthwhile investment.

“I try to do everything that I can to hang on to these old boys,” he says.