Outdoors, TIMES UNION MAY 19, 2025
By Roger Hannigan Gilson, Staff Writer, Times Uniton May 17, 2025
Invasives have largely wiped out the American chestnut and elm, caused “hell” with the beech, and are now wreaking havoc on the eastern hemlock and white ash. Signs of beech bark disease on the bark of an American beech tree. It is one of five species in the region that have been severely affected by invasives in recent decades.
TANNERSVILLE — Marc Wolf steps off a trail at the Mountaintop Arboretum to examine a beech tree with mottled, bumpy bark.
“This is pretty typical of beech bark disease,” he said. “Beech trees would typically have a perfectly smooth, grey, beautiful bark … and then they start to see this puckering. To me, it looks like they start to have leprosy.”
Wolf is the horticulturist for the arboretum, overseeing more than 30 tree species over 200 acres. Five of those are being attacked by invasive species.
Over the past 140 years, fungi and insects from Europe and Asia have been introduced to ecosystems with no way of absorbing them. The invasives have spread across the region, chewing through native tree populations. Three arrived generations ago, while two hit recently and are still spreading.
Scientists have been trying to battle the invasive species and their effects on the trees, and the arboretum in Tannersville hosts some of their efforts. But mitigation attempts have failed in the past, and whether any of this work will help is yet to be seen.
Elm, chestnut and ‘beech hell’
The American elm and the American chestnut first flourished because of humans.
Michael Kudish, a botanist and the author of “The Catskill Forest: A History,” said elms were widely distributed in the floodplains of the Catskills and Hudson Valley before the arrival of Europeans, but settlers’ farming techniques helped the trees spread. The elm, which does not do well in shade, propagated at the edges of settler-cleared land, finding ample sunlight on the edges of farm fields and the sides of roads.
Then the disease came.
Dutch elm disease started devastating European elms in the Netherlands in 1919 and was first detected in New York in 1933. By World War II, it had spread throughout the Northeast, according to the National Park Service.
The disease is actually caused by two groups of invasive species: several varieties of elm bark beetle and two related fungi. The beetles spread the fungi from tree to tree, where they attack vascular tissue. The tree attempts to stop that spread by plugging the affected tissue, but that renders it unable to transport water along its length. It eventually dies of dehydration.
Kudish noted the opposing effects of humans on the elm. “You have an increase in elm population because of all the farming, and then following that, in the 1930s, you have the disease come along, which did the opposite — it reduced the population.”
Dutch elm disease is now found throughout the United States except in areas of the Southwest that have limited elm populations, according to the U.S. Department of Agriculture.
Native American tribes helped the American chestnut spread. Starting some 7,000 years ago, indigenous people would torch land west of what is now called the Hudson River to create better conditions for hunting, traveling and farming, Kudish said. After the fires burned the northern hardwoods that dominated the region, chestnut trees would often take their place, since their seeds sprout faster than competing species. The chestnut’s dominance stopped where the fires stopped: at the peak of the Catskill Escarpment, the steep eastern wall of the mountain formation.
The chestnut blight arrived in the late 1800s, when Americans seeking to introduce a chestnut tree with larger nuts inadvertently brought the blight along with it.
Erik Carlson, a postdoctoral associate with The American Chestnut Research and Restoration Project, part of the SUNY College of Environmental Science and Forestry, said the fungus arrived from Japan on a species called the Chinese chestnut. The fungus does not damage chestnut trees in Asia, since the two species evolved there together, but the American chestnut was different.
“It just started killing them wholesale,” Carlson said.
In towns and cities across the country, the soaring trees, which grow taller than 100 feet, were often planted along roads. Communities felled thousands of them, attempting to stop the blight’s spread. It had little effect.
The chestnut tree is now “functionally extinct,” Carlson said.
But there are still remnants of the elm and the chestnut in the Catskills. Charles Canham, a forest ecologist with the Cary Institute of Ecosystem Studies in Dutchess County, said there are still many elms at high elevations in the Catskills, where the trees are “managing to hide out” from the blight. But there is no indication that the bark beetle could not survive at high altitudes — which is to say, these elms may be living on borrowed time.
A map of American chestnut sprouts in the Catskills produced by researcher and author Michael Kudish. Though the mature trees are very rare because of the chestnut blights, some of their root systems remain because of the way the blight progresses.
The chestnut blight does not affect the tree’s root systems, so even after the trunk rots above ground, the tree can survive. The root system is capable of sprouting anew, Carlson said — only to again be attacked by the blight.
Some of these root systems “keep on reproducing for decades,” Carlson said. “But eventually, they run out of steam.”
Like the chestnut, the beech tree’s root systems survive its disease. Beech bark disease is caused by an invasive fungus that enters through holes bored by the beech scale insect, which is also invasive, according to an explainer by Gary Lovett for the Cary Institute.
The disease spread slowly, reaching the Catskills in the 1960s after being introduced in Nova Scotia in the late 1800s. Ironically, the total biomass of beech trees has increased in the Catskills since then, Canham said. That’s because the surviving root system of the beech usually sprouts anew. Their large, shallow root systems can produce many tree trunks, and the sprouts can soon grow into a large, dense cluster of saplings.
This is referred to as “beech hell,” Canham said, because of its impact on the surrounding forest. The saplings crowd out other species. Beech leaf disease takes out the trunks before they reach maturity.
Ash and hemlock
Two more recent invasive species are wreaking havoc on two key trees in upstate New York: the eastern hemlock and the white ash.
The hemlock woolly adelgid first came to the East Coast from Japan in 1951, hitting near Richmond, Va., before spreading across the eastern U.S. It was first discovered in New York in 1985 in the lower Hudson Valley and Long Island, according to the state Department of Environmental Conservation. The adelgid is now found throughout southern New York. Its range stretches north to Schenectady County, and the invasive was found in isolated spots in the Adirondacks in 2017.
The aphid-like insect lays eggs on hemlocks in large “woolly” masses. Once hatched, the juveniles feed on the trees for the rest of their lives, severely damaging them, according to the state Department of Environmental Conservation. The decimation of hemlock is especially concerning since it is considered a “foundation species,” which Cornell University defines as one that “creates the ecosystem in which it resides.” Hemlock is also the third-most-common tree in New York.
An eastern hemlock. Hemlock is considered a “foundation species,” which Cornell University defines as one that “creates the ecosystem in which it resides.”
Though in most cases, invasive diseases and insects have a broader climatic tolerance than the species they attack, this is not the case with the adelgid. Very cold winters can kill the insect, but temperatures do not drop low enough in the lower Hudson Valley. In the Catskills, adelgid populations wax and wane depending on the severity of the winters.
The white ash, as well as less common varieties of ash found in the Catskills, are being attacked by the emerald ash borer. The vividly colored insect was first discovered near Detroit in 2002, according to Michigan State University. It was first observed in New York in 2009, according to the Department of Environmental Conservation, and is now found throughout the state.
Canham said the borer spread faster than almost any other invasive species, and he expected ash populations in the Catskills to be “literally decimated,” with a loss of more than 90%.
Treating trees
At Mountaintop Arboretum, Wolf walks through a grove of ash trees, each with a colored ribbon tied around its trunk.
The trees are being injected with pesticides by a trio of scientists led by Cornell University forest entomologist Mark Whitmore. The different colors indicate which years they were treated. The first cohort received the injection in 2014.
So far, the outcomes appear positive. The pesticides’ effectiveness only lasts two or three years, so the trees must be reinjected. The arboretum hopes to save its ash trees by this method.
The treatment is unfeasible in larger ecosystems, since finding and injecting thousands of trees on a scheduled basis requires too much money and time. But researchers have been working, some for decades, on ways of defeating invasive species.
Marc Wolf, director of horticulture and environmental stewardship at Mountaintop Arboretum, points to ash trees that are being treated against emerald ash borers.
Carlson, the associate with The American Chestnut Research and Restoration Project, said efforts began with researchers trying to replace decimated native chestnut populations with Chinese chestnuts, the species that naturally coexisted with the blight in Asia and brought it to these shores. But the Chinese chestnut trees did not perform well. They grew slower and shorter than their American counterparts and were outcompeted by other, taller trees that stole sunlight.
The next major step came in 1980, Carlson said, when the American Chestnut Foundation was formed and began breeding American chestnut trees with Chinese chestnut trees. The goal was to “capture genetic variations related to blight … from Chinese chestnuts by selectively breeding American/Chinese hybrids while maximizing American chestnut ancestry,” according to the foundation.
The theory was that only a few genes controlled the Chinese chestnut’s resistance to the blight, Carlson said. But it turned out that many, many more did, derailing the effort.
The foundation is now trying a new approach. Researchers analyze the DNA profile of an American chestnut for genetic similarities to disease-resistant trees in the field. Researchers then breed the most disease-resistant trees available and repeat the process with their offspring, “until the average disease resistance is high enough for long-term survival in the wild,” according to the foundation.
The American Chestnut Research and Restoration Project also has a method for saving the American chestnut. Researchers took a gene from wheat that produces a detoxifying enzyme and inserted it into the genome of the chestnut. The resulting tree can break down a toxin created by the blight fungus that would otherwise kill the tree.
The organization calls the new tree the “Darling chestnut.”
Researchers found the gene about 15 years ago, Carlson said, and the blight-resistant tree started going through a federal regulatory process in 2020. The process is lengthy for genetically modified organisms, and the Darling chestnut must pass muster with the U.S. Department of Agriculture, the EPA, and the FDA, since chestnuts are edible.
Carlson estimated they had a year or two left.
“I’m looking forward to it, when I can plant (a chestnut tree) on my own property,” he said. “It’s something that we all look forward to.”