ByNancy Sheehan

PETERSHAM — Soon, there won’t be much snow dusting down on anyone from hemlock trees — at least not in Massachusetts or most of the Eastern U.S. A tiny insect has been encroaching ever northward sucking the green lifeblood out of any hemlock it finds, then moving on leaving behind only wooden skeletons on the forest floor.

It’s not a slow demise. The still verdant but thinning stands of hemlock you can see on a stroll through local forests today will virtually disappear from Massachusetts by 2025, scientists say. Climate change has opened the door for the insect, the woolly adelgid. The only thing known to stop its progression is extreme cold and, with warming temperatures, that thwarting threshold is in retreat.

A new outdoor site-specific exhibition at the Harvard Forest, called “Hemlock Hospice,” tells the story of the demise of the eastern hemlock within the context of climate change and the future of our New England forests.

David Buckley Borden, an interdisciplinary artist and designer, created the exhibition in collaboration with internationally noted scientist Aaron Ellison, Harvard Forest’s senior ecologist. It is designed to use art to communicate the latest scientific research being done at the forest, which serves as Harvard University’s center for forest research and education. “Hemlock Hospice” comprises 13 sculptures installed along an interpretative trail through the still magnificent, though now ailing, hemlocks on the forest’s Prospect Hill Tract.

The miles of peaceful pathways at Harvard Forest are always open to the public for hiking but they will be especially engaging when “Hemlock Hospice” opens Oct. 7. The opening event will feature talks and tours through the woods at a time when fall foliage is beginning to create a colorful backdrop to the ferny green of the hemlocks. The forest is about a 50-minute drive north of Worcester on Route 122, designated a Massachusetts scenic byway as it winds through Paxton, Rutland, Oakham and Barre before reaching Petersham, which has one of the most picturesque town commons in the state.

Borden, who has been in residence at the Harvard Forest for the past year, said he wanted the “Hemlock Hospice” trail to be an immersive experience that tells the story of the hemlock’s demise through a blend of science, art, and design. The aim is to encourage conversations among all the forest’s interested parties including ecologists, artists, foresters, journalists, naturalists and citizens seeking a woodland respite, all while getting everyone a little closer to being on the same page around ecological issues.

“This is in many respects a global warming issue,” Borden said, as he gave a tour to members of the press recently while the installation awaited finishing touches in preparation for opening day. “People always see the big storms, the hurricanes, the sea level rise, the flooding, but this is another example and it’s not as dramatic. It’s a slow burn as opposed a quick storm. But though it’s happening slowly, it has no less of an impact.”

About 90 percent of the materials used in the exhibition are recycled, including wood discarded by foresters and round saw blades rescued from an old mill. One of two sharp-toothed saw blades has been repurposed to show enlarged drawings of the adelgid, an aphid-like insect, while the other shows a wavy line in a two-toned design. The line is actually a graph representing how much average temperatures have warmed since records started being kept in 1880. It’s one of many ways Borden has embedded scientific research and data into some of the pieces to help tell the hemlocks’ story.

“This is about the idea that the forest is really suffering from a double assault — one, it’s the insect, and, two, it’s global warming,” he said. “So, on the saw blade, 1880 is the starting point of the data set for average temperature, and you can see after that it’s a really clear uptick.”

As the climate warms, the woolly adelgid has been moving steadily north. “You can basically track the northward progression by the last time in the winter that it reached minus 25 Centigrade (minus 13 Fahrenheit) at night. The next year, the adelgid shows up,” Ellison said. “So, in Groton, Connecticut, that was about 1981, and in Storrs it was about 1988 and at the Harvard Forest that’s about 2004. Now the adelgid is in the Adirondacks and Maine and it’s into Vermont because, as the climate warms, it can keep moving north.” Also, climate change is stressing the trees out, making them more susceptible to the adelgid, he said.

Throughout Harvard Forest, trees are rigged with cords, wires and various scientific monitors that measure everything from carbon uptake to sap flow. On one level, the show tells a sad story of loss, including the decline of scientific data that can no longer be gleaned from hemlocks because they are dying.

But there is a range of work in the show. One of the more fanciful pieces is a section of hemlock carved into the shape of a computer data stick that can be plugged into a hemlock stump. The center of the piece is an outsize version of a core sample, the plugs of wood scientists extract from the center of trees, although in actual practice they do so in pencil-slim pieces. The samples are used to determine a tree’s age among other things.

“It’s about the tree as a data source so this is designed as a hemlock data stick, or a memory stick,” Borden said. “It’s an abstraction of a tree core in exaggerated form. We made a really big one you can just plug in” to the stump.

The delightful “data stick” is meant to lighten the mood as visitors walk along the trail taking in other sculptures that foreshadow the end of the hemlock forest as we know it.

“We didn’t want it to be a doom and gloom project so we tried some hopeful and kind of fun things as interesting ways to look at something that could, potentially, be a downer, so there are a few kinds of campy pieces like this,” Borden said.

Another piece points out the species that will thrive in a hemlock-less forest. It is an open construction designed as an abstraction of a fast-forward sign that also can be viewed as a bunch of interlocking delta symbols from the Greek alphabet. The red, yellow and white painted piece shares the same color scheme as a lot of global-warming maps, which Borden says he has become obsessed with over the course of his residency at the forest.

The piece leads the eye to a nearby patch of low, tangled growth — black birch saplings eagerly taking hold in a forest that is becoming more open and sunny as the hemlock canopy thins. The scrappy birches are the first volunteers in a successional wave that will wash through the forest as the hemlocks die off. Eventually, the birches will be joined by oaks and maples as well as non-hemlock pines, forming a forest that will seem just fine to the casual observer out for a restorative walk in the woods. How many of us miss the majestic elms and mature chestnut trees we never knew because they were killed off by disease so long ago?

So, the forest will someday redefine itself but it will have to go through a rather awkward stage before getting there 30 years or so from now. “First, it’s going to be a big impenetrable birch thicket,” Borden said. “It’s impossible to move through it without getting slapped in the face and it’s a far cry from an open forest like this.”

Changes are always happening to forests, but usually at a pace far too slow to be noticed in one person’s lifetime. With the hemlocks, however, just a couple of decades after the insect first moves into an area, a beloved tree that has formed a foundation of our New England forests will all but vanish.

The culprit behind this disconcertingly quick change is not native to the U.S. The woolly adelgid originally came from Japan, arriving in Virginia in the 1950s on plants imported by a nursery.

“Some people brought a Japanese hemlock to some nursery in Virginia and someone bought it and put it in their back yard and the adelgid escaped,” Ellison said, “so it’s non-native and considered an invasive species.”

The insect has no natural enemies in the U.S. and so has been able to gorge itself in a predator-free environment all up and down the eastern part of the country.

Ellison is careful to stress that, from the scientific viewpoint, the adelgid didn’t intend to cause such havoc. “It didn’t get up and come here and apply for a visa and start spreading,” he said. “It was carried here and then it was, like, ‘I’ve got to eat’ just like if you moved to a new city or were refugee somewhere. You’ve got to figure out how to live and eat and this is what it does. It lives, it eats, it reproduces and then it moves on. It’s just another organism doing its thing.”

Not that Ellison is a big fan of losing all our hemlocks.

“It’s not that the adelgid isn’t a problem. It’s that the forest will be very different,” he said. “And if you want to walk through the hemlock forests that Robert Frost wrote poetry about, that Emily Dickenson wrote poetry about, they won’t be here. Is this a good thing or a bad thing? That’s for every individual to decide for themselves, but I think there is definitely something lost by taking this kind of forest out of our landscape.”

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