How the Climate Crisis and Pests Are Impacting Four Tree Species in Vermont’s Woods | Environment | Seven Days | Vermont's Independent Voice

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How the Climate Crisis and Pests Are Impacting Four Tree Species in Vermont’s Woods


Published April 21, 2021 at 10:00 a.m.
Updated May 11, 2021 at 2:33 p.m.

Brewster Uplands Conservation Trust, looking south toward Mount Mansfield - CALEB KENNA
  • Caleb Kenna
  • Brewster Uplands Conservation Trust, looking south toward Mount Mansfield

As truck traffic groaned down Montpelier's Main Street one recent Monday, John Snell paused by a large curbside ash tree whose trunk was nicked and scraped. Street trees don't have an easy life: bombarded with road salt, climbed by children and dinged by the occasional front bumper.

But the 15 green ash trees in downtown Montpelier face a greater threat than overzealous parkers. The city's tree board, which Snell cochairs, has treated them with an insecticide to ward off the emerald ash borer, an invasive bug first found in Vermont in 2018. Unchecked, the beetle can kill an area's ash trees in the space of five years, turning a line of street trees into brittle wooden skeletons.

"To use pesticides downtown wasn't something we did lightly," Snell said, "[but] we just knew we had to keep them. If we cut this tree out and planted another tree here, what we'd have is a little short tree for however many years."

Like Snell, foresters and tree lovers across Vermont are struggling to understand, and respond to, the growing number of threats to the state's mountain forests and urban treescapes as we now know them.

The state's forests have never been static. Humans have played a role for centuries; by the close of the 1800s, loggers and sheep farmers had stripped 80 percent of Vermont of its trees. Human choices and practices changed and, by the close of the 1900s, forests had rebounded to cover 80 percent of the state.

The human-induced climate crisis — compounded by global trade patterns that invite non-native pests — may present the greatest challenge to forest management yet. Vermont is becoming warmer and wetter, creating conditions that benefit insects and diseases capable of wiping out a species. While a single threat might not be enough to bring down a tree, compounding pressures can. Less-than-ideal soil conditions, for example, might stress a tree but not kill it. But that stress could make the tree more vulnerable to an insect, drought or herd of browsing deer.

Learning about the emerald ash borer is like opening an attic hatch and unleashing a shower of bugs and blights upon your head. Dutch elm disease killed 75 percent of elms across North America in the 20th century and is the reason cities such as Montpelier have an Elm Street but few elm trees. Beech bark disease has been killing Vermont beech trees for decades. The southern pine beetle is steadily marching northward. The hemlock woolly adelgid has infested its namesake trees in southern Vermont.

"How hard are we willing to resist and fight? And when do we start saying, 'We're overwhelmed and there's just too many things'?" asked professor Tony D'Amato, director of the University of Vermont's forestry program.

"We're not at that point right now," he said. "But maybe in 50 years, add seven more beetles and 10 more invasive plants, and then that might be a pretty tough scenario."

To explore those questions, Seven Days looked at the current health and likely future of four species at home — or once at home — in Vermont. Because the climate crisis and other threats are human-driven, are we not obligated to help our forests adapt? Or would such actions constitute further meddling in natural processes? Should we work to maintain forest species as we know them now or strive to engineer forests better suited to Vermont's future climate?

D'Amato advocates "a big dose of humility." Humans who set out to alter a forest landscape should heed the words of conservationist and wildlife ecologist Aldo Leopold, who said: "To keep every cog and wheel is the first precaution of intelligent tinkering." In other words, value every plant and animal and keep your options open.

"When you're thinking about Vermont's forests and managing for the future, you're still trying to factor in that there might be some species, or there might be some attributes, that we don't even know are important," D'Amato said. "So let's make sure we're conserving those as we do some of these actions, because they might be pretty important as part of the ability of Vermont's forests to be resilient into the future."

Forest stewards can work to preserve plant species, trim back their competitors and even move them to new sites where they're better equipped to survive. But, as state botanist Bob Popp, who studies Vermont's rarest plants, mused, "At what point does it become gardening?"

Ash — Green, Black and White

Green Ash, Fraxinus pennsylvanica - JEANIE WILLIAMS
  • Jeanie Williams
  • Green Ash, Fraxinus pennsylvanica

Three species of ash — green, black and white — comprise about 5 percent of Vermont's forests. Little can be done to save many of those 150 million trees, foresters say, since most have no resistance to the emerald ash borer.

But in Vermont cities and towns, where ash are a valued shade tree in backyards and along roadways, towns and landowners are working to slow the insect's spread.

Once a tree dies, it becomes much more expensive and dangerous to remove. So homeowners and arborists have three choices: remove ash trees promptly, before the bug can get to them; wait for signs of the borer, then begin removing trees; or inoculate trees with an insecticide to protect them from the beetle.

Inoculation, which has to be done every two to three years, is not practical for a majority of trees, so cutting them down is the most common approach. In Williston, where 51 percent of street trees were ash as of 2014, officials began removing them and replanting other species in 2015. They've removed and replaced about 190 trees so far, according to Melinda Scott, the town's conservation planner.

In Burlington, arborists haven't yet removed many ash trees, but they're anticipating it, according to city arborist Vincent Comai. Currently, the Department of Parks, Recreation & Waterfront is planting other trees between the city's streetside ash so that when the ash are removed, established trees will remain. "To date, we have already planted replacement trees for just shy of 50 percent of our greenbelt ash," Comai said. "We've got a hell of a jump start."

Preventive cutting alarms Don Stevens, chief of the Nulhegan Band of the Coosuk-Abenaki Nation. The cure has the same effect as the disease, he said: "People cutting them down to try to prevent it — [they're] doing the work of the borer."

Black ash, which grows in wetter, swampy areas, is particularly significant to the Abenaki. The tree is part of the tribe's creation story and the source of the material its members use in weaving baskets.

"Trees have sap running through their veins like we have blood running through ours, which both contain life-giving water," said Stevens. "It connects us to that environment and web of life."

He and other tribal members have spoken with towns about the trees, encouraging them to salvage and protect rather than remove living trees.

"They're looking at it from a cost and liability standpoint," Stevens said of those ready to preemptively cut down the ash. "You have to look at it as preservation. What do these trees do? What do they mean?"

Trees in Shoreham - CALEB KENNA
  • Caleb Kenna
  • Trees in Shoreham

The emerald ash borer, the source of this dilemma, is a pretty bug. Metallic green with hints of copper and a reddish body under its bladelike wings, it's small enough to fit on a penny. In its native Asia, the borer feeds on Chinese and Japanese ash species and is merely a nuisance. The trees have developed natural resistance, and the bug's population is kept in check by predators.

But possibly as early as the 1980s, the emerald ash borer hitched a ride across the Pacific Ocean, likely in a shipping crate. Most North American ash trees had no natural resistance, and no insect predators hunted the bug. By the time it was discovered in Michigan in 2002, the borer had begun an unstoppable march across the United States — west into Colorado, south into Louisiana and north into New England.

In Montpelier, the borer has landed in a line of green ash outside the hilltop office of the National Life Group. The golden dome of the Statehouse is visible between the trees' branches. To the untrained eye of a reporter, there was no visible damage to the trees, which National Life Group is treating with insecticides.

Just down the hill, the city is using similar treatments to protect curbside trees that provide shade, an increasingly important service in the era of the climate crisis. Board chair Snell has taken thermal images of the corner of State and Main streets in the summer. On one sweltering day, the crosswalk had heated to 133 degrees Fahrenheit; in the shade of the ash trees, the sidewalk was just 77 degrees.

Human movement plays a huge role in how pests spread. On its own, the emerald ash borer would naturally only spread one to two miles per year. But the movement of ash wood by people, especially as firewood, has allowed the beetle to spread much more quickly, despite attempts at education and firewood quarantines.

Josh Halman, a forest health specialist at the Vermont Department of Forests, Parks and Recreation, said there may be biological controls for the emerald ash borer. A lab in Michigan is raising parasitoid wasps that feed on the borer's larvae and reduce populations, a method that "has been showing promise," Halman said, during trials in 30 states, including Vermont.

It might seem like lot of effort, but the impacts of ash on the landscape go far beyond shade on urban streets. Snell pointed out that dozens of insect species rely on ash for food.

"There are entire ecosystems that are based off interplay of many species of trees and plants," said Joanne Garton, technical assistance coordinator for the Vermont Urban & Community Forestry program. "You take out one piece, and you don't know what the reverberations are."

American Chestnut

American Chestnut, Castanea dentata - JEANIE WILLIAMS
  • Jeanie Williams
  • American Chestnut, Castanea dentata

The largest American chestnut in Vermont is dying.

For years, it and two other chestnut trees near a road in rural Berlin were holdouts, the remnants of a species that once blanketed the eastern U.S. Today, only two of those 80-year-old trees are left. They stand in a patch of forest on ground so thick with leaves that it's soft and spongy underfoot.

The state record holder is tall and sprawling, but the bark has sloughed off its upper branches, now stark like scaffolding against the sky. Inside the deep-set rivulet patterns on its bark are hints of orange, a telltale sign. The tree is a victim of a fungus called chestnut blight, which eats away at the layer of cells just under the bark where new growth begins. Eventually it girdles the tree, cutting off nutrient flow and killing it.

Perhaps because they live at the northernmost edge of the tree's range, the Berlin chestnuts escaped the functional extinction of their species in the first half of the 20th century. But now the two remaining trees are "just about dead," said Burlington's Kendra Collins, the American Chestnut Foundation's New England regional science coordinator. And Collins would know — she spends much of her time with dying chestnuts as part of an effort to restore the species.

On a secluded parcel at UVM's Horticulture Research and Education Center in South Burlington this month, she stood among rows of planted chestnuts of varying sizes, many displaying blight in prominent orange cankers across the bark. As she walked, Collins talked about the 40-year, uphill battle to breed a blight-resistant American chestnut.

"You have to plant an awful lot of them, challenge an awful lot of them and keep very few," Collins said. "The hope from early breeders was that this [was] a really simple trait to pass on ... one gene, like giving your child your eye color. It is not nearly that simple."

Since the 1980s, the foundation has been cross-breeding American chestnuts with blight-resistant Chinese chestnuts, hoping to create a tree that looks and acts like an American chestnut but can withstand the blight. Researchers repeatedly cross the offspring of American and Chinese chestnut with other American chestnuts to recover American characteristics, Collins explained.

"We want to get as close to the American tree as we can, because we know that tree evolved to grow in our forests," she said. "That tree has the tools it needs to live in the eastern United States ... [Chinese chestnuts] don't compete in our forests."

Collins exposes trees from each crossing to the blight to understand how resistant they are. Resistance operates more like a continuum than an on-off switch. The goal isn't a tree that's immune to blight but one that can tolerate it and survive its attacks. After establishing a crossed species with the characteristics she wants, Collins will breed it with another crossed species and test those trees, too.

It's a slow process that requires countless hours of volunteer citizen scientists who plant chestnut crosses in backyards and parks and track their progress.

Researchers in New York have developed a different, more controversial tool. They've genetically modified a blight-tolerant American chestnut and are seeking U.S. Department of Agriculture approval to distribute the trees widely. It would be the first genetically modified organism designed and approved to reproduce in the wild, the researchers say.

"They've given [the American chestnut] one gene that imparts blight tolerance and, so far, does not look to have any other ill effects," Collins said.

Otter Creek in Middlebury - CALEB KENNA
  • Caleb Kenna
  • Otter Creek in Middlebury

Just as there are divisions about how humankind should combat the emerald ash borer, not everyone is happy with the genetic engineering approach. Two board members of the Massachusetts and Rhode Island chapters of the American Chestnut Foundation resigned in protest of the organization's support of the genetically modified tree, and anti-GMO groups led public campaigns against the New York researchers' petition for federal approval.

Even with a federal go-ahead, plenty of testing and controlled planting are still necessary before the trees are planted widely, Collins noted. "We would have to plant, I think, two and a half million trees every year for 200 years to actually restore the ecological function of [American chestnuts]," she said. "Right now we plant 30,000 a year, maybe, across the [species'] whole range."

Yurij Bihun, a forest resources analyst and former president of the Vermont/New Hampshire chapter of the American Chestnut Foundation, said some chestnut restoration volunteers have a personal history with chestnut trees.

"Then there are people like me, who are foresters or scientists, who see this as a challenge that hasn't been met," he said. "No one has taken on a large-scale restoration of a species like this ... There are people that are just willing to see if we can move this along — and are hopeful that, with some luck and science and hard work, we get here."

Collins hopes chestnut restoration will provide lessons in how to stave off pests that threaten other species.

"I think the possibility of working toward fixing something that we, as humans, broke — that piece appeals to a lot of people," she said.

Red Spruce

Red Spruce, Picea rubens - JEANIE WILLIAMS
  • Jeanie Williams
  • Red Spruce, Picea rubens

Hikers climbing in the Green Mountains ascend through a layer cake of ecosystems, from lower-lying hardwood forest to the nearly treeless alpine tundra atop Mount Mansfield and Camel's Hump. Between these two zones, at roughly 3,000 feet, hikers find themselves in stands of evergreens dominated by red spruce and balsam fir.

"When I pass that threshold where I'm now into the conifers — you're pretty late in your hike ... and you're getting kind of tired, but it's getting cooler," said Kenna Rewcastle, a doctoral student at UVM's Rubenstein School of Environment and Natural Resources. "It almost has this ethereal feel to it, because there's more mist. There's moss everywhere. The colors of the forest change. It's not just a change in tree species but a total change in the ecosystem."

Those red spruce, in particular, demonstrate that what humankind damages, humankind can, sometimes, help to mend.

Under the best conditions, a red spruce can live 400 years and grow 75 feet tall. Its wood is particularly valued for making musical instruments; the Abenaki used its sap to seal canoes and its needles for medicinal tea. A carbohydrate layer under the bark is edible, in a pinch, Chief Stevens said.

A dominant species in Vermont's precolonial forests, red spruce was largely cut off in the heyday of logging. As forests later regrew, hardwoods became more dominant; red spruce retreated to high elevation and parts of the state with poor soils in which species such as maple cannot thrive.

But even when timber cutters turned their attention to other species, humans weren't done with red spruce. In the early 1980s, UVM researchers began to sound the alarm: Red spruce, particularly on Camel's Hump, were dying. The blame fell on acid rain, created by emissions from power plants and gasoline-fueled engines. Scientists' warnings helped usher in the 1990 amendments to the Clean Air Act that began to curb those emissions and reduce the acidity of rainfall.

Stands of spruce responded. A 2018 study by researchers from UVM and the USDA Forest Service's Northern Research Station found that 75 percent of red spruce trees across five states had grown in size since 2001.

In 2008, UVM ecologist Brian Beckage was the lead author on a paper that estimated the boundary between northern hardwood stands and the spruce-fir boreal forest was moving upslope at a rapid clip (rapid for forests, that is, which "move" by depositing seeds and growing new trees).

But in 2015, D'Amato, the UVM forestry researcher, and a University of Minnesota forest ecologist conducted a wider survey and came to a different conclusion: that the softwood-hardwood boundary had remained stable or shifted slightly downward by an average 1.5 meters every year in the Green Mountains. The authors hypothesized that, though the warming climate was pushing the boundary upward, the recovery of red spruce and the decline of harvesting was counteracting the climate impact.

"Just driving around Vermont, when you look at where the hardwoods end and the spruce begins, it's often a pretty linear line," D'Amato said. "And that's a pretty human-generated line in some places, where people were cutting up the mountain and taking the spruce out.

"Next time you're out in the woods," he suggested, "look as you start to enter into that spruce-fir zone. Just downslope from that, you start seeing a lot of young spruce. So we've been seeing this passive recovery of that species into places where it likely was in 1850."

Tree in Weybridge - CALEB KENNA
  • Caleb Kenna
  • Tree in Weybridge

Of bigger concern to D'Amato is the balsam fir, which often grows with red spruce at high elevations and in the Northeast Kingdom. Vermont is the southern end of its range.

"That's a species that I think many of us are concerned will experience pretty significant impacts over time as things get warmer," he said. "It's already somewhat outside of the center of its climate niche, and so it's much more vulnerable to any slight change in that condition."

Mike DeBonis, a forester and executive director of the Green Mountain Club, said that the changes on mountaintops will likely be site-specific. More rain and heavier storms could cause blowdowns, create new openings in the canopy and affect soil retention. And the growing number of hikers — trail use rose by 35 percent last year — creates more wear and tear and more risk to the fragile alpine ecosystem.

"The species change is going to take time, but some of the things that people are going to notice now are the big storm events and maybe more invasive species," DeBonis said. "There's definitely real impacts [on] our management, like where we put trails, how we design them, how big infrastructure has to be, how we manage use and how we interact with the public."

Sugar Maple

Sugar Maple, Acer saccharum -  - JEANIE WILLIAMS
  • Jeanie Williams
  • Sugar Maple, Acer saccharum

At first, it might seem counterintuitive to plant red maple in a sugar maple forest. Red maples can be tapped, but the sap is a little less sweet, meaning it requires more boiling to make desirable syrup. Red maple doesn't live as long as sugar maple, but it has a few advantages: a broader range, more adaptability to different conditions, and characteristics unappealing to the forest tent caterpillar, a pest that munches sugar maple leaves with abandon.

At UVM's Proctor Maple Research Center, researchers have tapped more and more red maples; the trees now account for some 25 percent of taps, according to Mark Isselhardt, UVM Extension's maple specialist.

"Sugar makers absolutely pay attention to the species mix," Isselhardt said. "It's been heartening that there has been an increased approach of adding diversity in their woods. The [forest with] classic, widely spaced, big legacy sugar maples with very little understory is really an image from the past."

A diverse forest is more resistant to the impacts of invasive species and diseases, whereas a monoculture is vulnerable to a single, sweeping threat.

David Marvin, founder of Butternut Mountain Farm, an international maple supplier based in Morrisville, is also a consulting forester whose team assists landowners in managing 100,000 acres of woods. In a conversation about sugar maples, he spoke of the importance of the butternut trees on his family's 1,650 acres. Butternut trees were never a dominant species there, but now their numbers have been greatly reduced by a deadly fungus.

"Even a native insect like the forest tent caterpillar that has a preference for some species over others can just move through a whole stand very rapidly," Marvin said, "because there are no other species to interrupt that stand and to break up the banquet."

Sugaring has been integral to Vermont's identity since Indigenous people taught white settlers how to tap maples. The state is the country's top maple producer. The UVM Center for Rural Studies found that the maple industry contributed more than $300 million to the Vermont economy in 2013 — not including the spending of leaf peepers in the fall.

The importance of the sugar maple has led in recent years to a flurry of studies and news articles about whether and how the climate crisis might affect Vermont's maple industry. They often posit a gloomy future: Sugar maple forests may slowly retreat north; warmer winters mean a shorter sugaring season. But the UVM researchers say the story is more complicated than that.

"Everybody wants to lump trees into either being a winner or a loser," D'Amato said. "The way I always look at it, because I am a sports fan, is that the last team in the standings still wins some games sometimes."

Isselhardt, too, thinks many stories on maple are "unnecessarily" gloom and doom. Despite the fact that between 1965 and 2015 Vermont lost about 3.3 days of the sugaring season due to warmer weather, syrup production in Vermont has increased steadily since the 1990s. Vermont sugar makers are tapping more trees and using new technology to get a higher yield from each tap.

Another concern is that tree species acclimated to warmer weather will spread their range north as climate temperatures rise and will displace sugar maples until the maples' ideal range shifts northward out of Vermont. But this theory of species migration, Isselhardt pointed out, assumes individuals on the ground aren't doing anything to counteract it.

"Sugar makers are not going to wake up one day and be like, 'Why are all these oak trees growing in my sugar bush?'" Isselhardt said. "They are very active managers." Marvin and his employees, for example, pull out invasive Japanese honeysuckle by hand or burn it off with a propane torch.

Warmer late-winter weather can cut short sugaring season, as it did this year. Eric Sorkin, co-owner of Fairfax's Runamok Maple, estimated that most producers in the region saw only 50 to 65 percent of their average annual crop. Even if average temperatures change only slightly, he said, weather volatility worries him.

Isselhardt said the most likely immediate effect of the climate crisis on sugaring is an increase in these weather anomalies. The trees won't die, but the sugaring yields may become inconsistent.

Marvin said he's relatively optimistic for the sugar maples but concerned about the other species that have faded in his forests. He saw the decline of the elm trees, is watching beech and butternut disappear, and knows the future of the ash is bleak.

"I only can think of a couple of trees that are healthy now," Marvin said of the butternut. "But it's not valuable enough for people to care that much ... It never had the value, either aesthetically or economically, to engender the kind of research and work that ash and maple and elm have had."

As Marvin knows, the story of the climate crisis and Vermont's forests can't focus only on maples. We have to think about the overall forest and its individual species at the same time and learn to look at the world through both a micro and a macro lens.

"As long as you can look out the window and see a forested landscape and, in the summer, see that it's green, you're very likely to say, 'So what's the problem?'" Marvin said. "A healthy forest here is not just maple syrup and timber and toilet paper and newsprint. It's water quality and production of oxygen and sequestering carbon. These ecosystem services are critical to life — human life."

Find out more about the health of Vermont forests at, and

The original print version of this article was headlined "The Forest and The Trees"

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