What We Lose When We Lose Old-Growth Forests

The presence of absence is everywhere.

“Most people would walk through and think, It’s a beautiful forest. They don’t see what is on the way out,” said Neil Pederson, a senior ecologist at the Harvard Forest in Petersham, MA. He is talking about an old-growth forest in New York’s Adirondack Park that has probably never been cut. 

Pederson coleads a team of researchers working in old-growth forests in the Northeastern U.S., where they are uncovering a stark truth: even in protected forests, a siege is underway, waged by invasive insects and pathogens brought into the country inadvertently on packing material and nursery stock via global trade.

This is not an environmental crisis the public is used to: there are no loggers, no wildfires, no developers’ bulldozers. There aren’t even visible signs of people here. No buildings, no wires, no roads—not even trails. To the untutored eye, this forest looks fine. Some of the biggest, oldest trees are too wide at their trunk for human arms to reach around. Cathedral light filters through the tops of the trees, and sunflecks glow on deep forest duff. The quiet is velvety, dimensional. These trees, some standing for centuries, unspool their long stories uninterrupted by the noise of people.

Yet disease and death stalk this wood, coming for trees old and young. “I call it a quiet pandemic. We are working in forests that are in late stages of decline,” Pederson said. In forests all over the Northeast, the big beeches are already gone. The eastern hemlocks are gray and dying. Ash trees are succumbing to relentless attack. 

Change is normal in forests, and extinction is too. But these are not natural deaths—neither in the cause nor in the speed of destruction, with entire species being taken out in just decades. Scientists cannot believe the losses they are witnessing over their careers: losses of trees that should persist far beyond a human lifetime. Even in protected old-growth forests, elders that have stood for centuries have already passed—way before their time. These time scales, ancient and human, shock and reveal.

Old trees matter, explained David Orwig, colead scientist on the project and a senior forest ecologist at the Harvard Forest. “They feel different and look different, and they are different—they are rare,” said Orwig. “They have such a presence. There is that wonderment. I call them the magical forest.” Old-growth trees also are irreplaceable living archives, older than any instrument record, Orwig noted. And big, old trees are needed to help save the planet.

Orwig co-authored a 2018 paper that found that, across 48 forest plots around the world, the largest 1% of trees comprised on average 50% of the aboveground biomass. That points to just how important big, old trees are as carbon sinks blunting climate change. 

“They are the ones storing the vast majority of the carbon, and they also have amazing microhabitats in their crown, completely different plants up there you would never think of,” Orwig said. “Flying squirrels, raptors, they love being in big, old trees.” The research team last summer was astonished by a black snake climbing an old tree to get into its crown. Who knew snakes could climb?

Protecting mature and old forests is an essential strategy in the fight against climate change, but it has not received the attention it deserves, argued Beverly Law, professor emeritus in the Department of Forest Ecosystems and Society at Oregon State University. The world’s forests pull about one third of all human-caused carbon dioxide emissions from the atmosphere each year. Old-growth trees, in particular, store enormous amounts of carbon because of their tremendous mass above and below the ground. A strategic forest carbon reserve program that focuses on mature and old forests could protect biodiversity and blunt climate change, Law and her co-authors documented in a 2021 paper. Retaining and growing mature and old-growth forests is a key strategy to protect climate, biodiversity, and water and air quality, to provide flood and erosion control, and to offer unique beauty and spiritual refuge. 

Yet we are losing trees by the millions to invasive insects and pathogens. In a 2020 paper, lead author Kristina J. Anderson-Teixeira of the Smithsonian Conservation Biology Institute and her co-authors found that, in the Blue Ridge Mountains of Virginia, one in four tree deaths in the past three decades was linked to invasive species. 

The team feels urgency in their fieldwork. “It’s the rapidity of change people don’t realize. Old-growth trees that have been there for centuries are being wiped out—that is what is so sobering,” Pederson said. “We are catching the last whispers of beech. You see a hemlock and think, Oh, I’ll get that the next time, but it may be gone.”

Laura Smith was interviewing an elder who happened to be a tree. In a world of screen swipes and digital bytes, her tools for inquiry were low tech and hands on: wood glue, sand paper, masking tape. At the Tree Ring Lab at the Harvard Forest, her subject was PP317: a core she had carefully slid from the heart of an old-growth hemlock in New York’s Adirondack Park. I had watched her, weeks before, as she leaned into the tree’s trunk with a borer, shouldering its handle to press it deeper. The hemlock talked back with a loud creak at each turn.

That was the coring crew’s second day out during a week in the Adirondacks. An Eastern old-growth forest does not have the towering druidic gravitas of other old-growth forests, such as those in the Pacific Northwest. The Northeastern species the team was sampling are different: sugar maple, white pine, eastern hemlock. All survivors somehow missed more than a century ago in the cutting that took nearly all of the primary forest of this region.

But in 1894, the people of the state of New York declared 2.6 million acres of forestland off limits to future cutting or any commercial use, in one of the most adamant protective decrees ever anywhere in the world, setting aside a forest reserve to remain forever wild in the state constitution. In their rarity, the old-growth denizens of this forest command the respect—and the scientific interest—due survivors.

With each turn of the borer, Smith, a research assistant at the Harvard Forest, quested through the tree’s present to its deep-time past. Finally at the tree’s heart, she paused and gently slid the tray out of the borer. Cradled in it was the core: a slender, biscuit-colored wand of time and a panoramic window into the past. I leaned in close and saw the core was still moist with life. Smith paused and held the core in her palms, respecting the moment this tree’s story was first revealed.

She slid the core carefully into a plastic tube no bigger than a drinking straw, which was carried in a case with dozens of others gathered by the sampling crew that day for the long hike back to the car and the drive back to the lab.

It had been a good day for the crew at the end of a summer spent working on an ambitious mission to analyze cores from some 7,600 individual old-growth trees over more than 154,000 square miles of the Northeastern U.S. during the next several years. This is a wider geography and deeper timescale than has been previously attempted. Scientists hope to understand what the histories of these trees may tell us about how forests will respond to future shocks. Though such predictions are just that—no tree alive today has experienced what could be coming with the combined effects of globalization, climate warming, and invasive species.

It’s the dance of trees together over miles and centuries that these scientists are seeking, as well as the rhythms of growth and decline and synchrony across space and time. They are looking for clues in the past of these trees, written in their cores, to see how these forests have responded to big events. The killing frosts, parched droughts—disturbances large and severe enough to affect growth and regeneration, and even to kill.

Smith held up the core she pulled that day in the woods from the hemlock PP317.

Now mounted on a slender wooden block back at the lab, the core was ready to work up. First with a belt sander, then by hand with ever-finer sandpaper, Smith smoothed the core down, seeking its story. She gradually revealed clearly segmented rings of annual growth.

In any tree, tight and narrow rings show a tree biding its time, not doing much—something is holding it back. Wide rings show a release from constraint and growth spurt when some bonanza of fresh opportunity arises. Had a tree fallen nearby, bathing the tree in sun? Or was there an event of bigger impact and scale? One core shows these events in a particular tree’s history. To get the bigger picture, the team cores multiple trees in the same study plot, then across a wide area, to look for larger patterns. The forest for the trees.

Built to take it, trees can’t run away from whatever comes; instead, they are adapted to be brilliant strategists. Trees can resize as needed, dying back and stunting themselves in tough times, then releasing their growth when opportunities arise. And they are consummate diplomats.

Year by year, every tree writes its autobiography, and the elders in any grove record wisdom earned over many centuries. How they got along and managed with their neighbors, the changes in their community, the days of harmony, strife, and struggle, and seasons of feast and famine. Intimate diaries of their long years are recorded, in unstinting detail. Feats of solo virtuosity and brilliant synchronous enactments of agency across vast geographies are all forever inscribed. These are epic memoirs, told in the quietest of voices: the cores of old-growth trees. They recount the agency of trees. How they make their place. Stand their ground. Endure. We can learn from these mentors, here long before us.

Smith slid the sanded core of PP317 under the microscope and clicked on its light. She fed the core with her right hand under its lens, and with her left, she laid down a tiny dot with a pencil on the mounting block as she scanned through tree time.

Every decade got a tiny penciled dot. Fifty years got two dots, one hundred years three.

Her lips moved as Smith quietly counted off the years. “There’s a century, two,” Smith said. “We are back to 1850. 1800. 1774 is the earliest ring.”

This hemlock has abided since before there was a United States, before there was a state of New York or an Adirondack Park. Since the first people utilized this place—and since the time of their resistance against colonizers who would soon cut most of these trees. The colonizers are why today there are so few old-growth stands left anywhere, but especially in the Northeast of North America. Smith said she felt the weight of interpreting the tree’s story, as she logged images of the core in the digital database the team was building. The core itself would be stored in the permanent collection archived at the Harvard Forest.

After a day of hard searching last summer, purely by accident, the team located a stand of eastern hemlock on a preserve in northwestern Pennsylvania. When the team stumbled upon the trees, Pederson wept with relief. They were still there. Still standing. Still alive, for 500 and more years, some of the oldest eastern hemlocks known.

In his career at the Harvard Forest, Orwig has centered much of his research on the effects of the hemlock woolly adelgid, an invasive insect that wasn’t even present in the Harvard Forest when he arrived as a senior staff scientist in the 1990s. He once used the groves of hemlock at the Harvard Forest as his reference point, Orwig said, for what a healthy hemlock forest should look like. But then the insect continued its northward march and the forest became, as researchers have come to call it, a hemlock hospice. They are studying what happens when a species starts to die out. It’s not just a sentimental matter; losing an entire species of tree resets a forest’s regime, from how much water it uses to the animals it can nurture. It will still be a forest, but it is a different forest.

Curation and preservation of some populations of ash, of beech, of hemlock are necessary at least at some scale, Orwig argued. And society has got to spend what it takes to be more careful in a globalized economy. Current practices have led to the introduction of more than two nonnative insects into U.S. forests every year over the last 150 years. Invaders are everywhere, not only in the East. In the West, white pine blister rust is killing whitebark pine, now in need of endangered species protection.

Trees have genius, they have agency. Their long stories show what they are capable of. But they are no match for the intertwined effects of global trade, invasives, and climate warming. The 10,000-year run of eastern hemlock is coming to an end, and other species are on their way out or already gone.

Hemlock. Ash. Beech. Chestnut. Elm. A roll call of the lost. “They are a monument to our capitalist system,” Pederson said of the epidemics of invasives. “Money comes first. These forest systems took millennia to develop. We don’t even know what we are losing.”

But the People of the Dawnland do.

People of the Wabanaki Confederacy have called the lands and waters stretching from present-day Newfoundland, Canada to Massachusetts home for some 12,000 years. The Wabanaki are comprised of five principal nations: the Mi’kmaq, Maliseet, Passamaquoddy, Penobscot, and Abenaki. The People of the Dawnland, where the sun first touches the North American continent, know these forests, the animals, and the rivers of their territory as their relatives. And the old trees that can still be found here are respected as elders.

“The ancient wisdom is there,” said Gabriel Frey, a Passamaquoddy basket maker. While he lives and works in Orono, Maine, he carries the memory of a visit to California’s Sequoia National Park. Being in an old grove of trees affects him the same way a cathedral would, Frey said. “I whisper. You are in the presence of giants. It’s a different relationship with time.”

Now he and other basket makers are in a race against time to pass their tradition—one of the oldest known art forms in New England—onto the next generation as brown ash trees are wiped out in state after state by the emerald ash borer. Probably introduced sometime in the 1990s, the borer is on a relentless death march across the country, killing millions of ash trees of every variety in at least 36 states so far. 

Wabanaki teachings of reciprocity and responsibility in living with all their nonhuman relations for the benefit of future generations are no match for this onslaught of invaders.

For the Wabanaki, the loss of the ash tree is a deep blow to their culture. The tree is uniquely suited to their basket making because of where and how it grows and how it can be worked. The Wabanaki call brown ash the basket tree. It also is at the heart of their creation story.

“Most people can’t comprehend the effects of climate change; it is too immense,” Frey said. “When I first heard about the emerald ash borer, it was like that for me—I could not grasp it. To come to grips with the death of this species, the emotional impact is just as immense. That after 12,000 years, my kids will not be able to pass this art form on to their kids.”

As we spoke, Frey was selling baskets at the Wabanaki Winter Market, an annual event that draws Native artisans from all over the region. Frey is a star of the younger generation of basket makers, and collectors were lining up to buy his work. I asked Frey what he thinks about when he thinks of the future. Frey paused his work finishing a piece, a fancy basket woven from ash strips with mussel shells set in silver and brass on the lid. It’s the sort of work he has become famous for: an artistry that spans both contemporary styles and traditional techniques and teachings.

Frey is descended from a long line of basket makers who have gathered their materials from these same forests for generations. The wisdom of his elders has always called for taking only what was needed, expressing gratitude to the tree, and preserving ash for the next generation so there would always be enough to carry on their culture. There is no substitute for this tree, or their work.

And now? 

Frey leveled his gaze, quieted his hands, and spoke his testimony of what comes in defying the wisdom of elders in their teachings of reciprocity, of responsibility.

He said he has had to make peace with a future that is potentially without ash.

“What else are you going to do? If there is a solution to the problem, worrying about it won’t find it, and if there isn’t a solution, worrying won’t help. I don’t have any answers. I’m still hopeful,” Frey said. 

“How can you not be? I think having the ability to see all the shadow as well as the sunlight is important because we don’t live in a black-and-white world, either wanting to be all doom and gloom or rainbows and butterflies. The Earth is going to be fine, that is the hopeful part.”