Why Old-Growth Trees Are Crucial to Fighting Climate Change

Nature is already socking away a lot of carbon for us. It could soak up a lot more—if we help.
37%: The part that “natural climate solutions” could play between now and 2030 to keep global temperature rise below 2 degrees C.Video: Cody Cobb

Ken Bible steps over a carpet of bracken and vanilla leaf to get closer to the big Douglas fir. He gives its furrowed bark an affectionate slap, as if introducing a prize racehorse.

“It's about 70 meters tall and 2.6 meters in diameter,” Bible says, leaning back to take in the behemoth stretching above him. From way down here on the shady floor of the forest, he has no hope of seeing all the way to the tree's top. But thanks to a 279-foot-high tower that rises above the trees, Bible, who helps manage this site on behalf of the US Forest Service, has had the chance to know this old Doug from above as well as below.


Illustration: Alvaro Dominguez

From hundreds of feet up, at canopy level, he says, you begin to get a new vision of the complexity of structure that defines an old forest. “It looks like a mountain range,” Bible says. “You've got ridges and peaks and valleys.” Singular trees like the big Doug reach high over their neighbors. At around 500 years of age, it isn't the oldest tree in the forest, but a lucky location near a wetland has made it one of the biggest.

The Doug is lucky in other ways too. Once upon a time, its particular seed happened to fall from a particular drying cone into what, hundreds of years later, would become a small section of protected old growth inside the Wind River Experimental Forest, a research area in southern Washington state originally created to study the best ways to exploit forests for human use. Just outside the confines of this 1,180-acre remnant of old forest, the trees of the Doug's generation are long gone. Some were killed by fire, others by pests, and others were removed by foresters who, for more than a century, had been using the area as a testing ground in their attempt to find the best ways to turn the great forests of the Northwest into profit.

It was here at Wind River, on the slopes of an ancient volcano above the Columbia River, that Northwestern forest researchers began in the early 1900s to engineer the protocols that would govern the industrial-scale removal of the region's trees. It was here, in large experimental plots, that they compared the merits of different timber species and tree genetics, of novel methods for replanting and spacing; here that their experiments convinced them that Douglas firs would be the cash crop of a new industry and that the industry's methods should favor large clear-cuts and burns; here, too, that more than 800 million seedlings were reared to replace all the forests that would be systematically logged across millions of acres of the Northwest over the coming decades. Those seedlings served to solve a problem the industry would know not as “deforestation” but as “inventory depletion.” According to the new protocols, the transplanted seedlings would be grown and harvested in plantations where every tree was the same age.


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Bible's big Douglas fir, and the old-growth acres around it, survived only because one of those early researchers, a Yale Forest School graduate named Thornton Taft Munger, insisted on establishing a control for their experiments. The purpose of research at Wind River was to improve on the efficiency of nature by replacing forests with human-engineered tree plantations, he argued—so of course the experimenters needed to maintain a bit of nature against which they could compare their success. (The idea of the reserve nevertheless seemed odd to at least one Forest Service director, who responded with incredulity that anyone would bother to protect something as mundane and inexhaustible as old growth. “We've got 20 million acres of virgin timber in the National Forests,” he wrote. “Why set up this special area?”) In the end, Munger got his permission and set about measuring tree growth within the protected forest as well as outside of it.


It was a visionary act, but even Munger—for whom the reserve is named—saw no inherent value in its quiet, needle-dusted acres of firs and hemlocks and cedars and alder, beyond their use in research. According to the orthodoxy of the day, old trees were worthless and wasteful: effete, slow-growing, and decaying relics that ought to be ripped out and replaced with young and vigorous plantations. “There is little satisfaction in working with a decadent old forest that is past redemption,” Munger told a conference of loggers in 1924. (He had a particular hatred for standing dead trees, known as snags, which are a common feature in mature forests. He once wrote an entire essay about snags, in which he argued that they deserve “outlawry”: “They stand, fringing the skyline like the teeth of a broken comb, in mute defiance of wind and decay, the dregs of the former forest, useless to civilization and a menace to life.”) This general contempt for old growth defined the field of forestry for decades. “We grew up thinking of old forests as biological deserts or cellulose cemeteries,” says Jerry Franklin, a forest ecologist now renowned as the father of a very different school of thought. “We climbed over huge piles of downed logs and woody debris, and we didn't think about anything other than how to get rid of it, how to liquidate it.”

The Doug is one of the oldest trees in the Wind River forest.

Photograph: Cody Cobb

By late in the 20th century, the timber industry and its methods were well established and, according to the historians Margaret Herring and Sarah Greene, Wind River “began to become almost a backwater of forest research, a museum of old experiments.” A large tract of Munger's old-growth section was nearly clear-cut in the 1960s—foresters agreed that its utility for research was exhausted, and it was still understood to have no other value—and the area was again threatened in the 1980s, when Congress decided it would be a good spot to test whether a military surplus balloon, lifted by four helicopters, could be used for logging in remote areas. (The project was abandoned when the contraption crashed during a test flight in New Jersey.) The Doug stayed lucky, and the forest stayed intact.

Excess brush and timber in forests can be removed to prevent wildfires and then slow-baked in a low-oxygen environment to create charcoal-like biochar. When buried, biochar can nourish parched agricultural soil, promote food production, increase water efficiency, and hold carbon in the ground for centuries.

It wasn't long before researchers were glad it had endured. Where once foresters had worked to study how to most efficiently remove wood from a landscape, a new generation of scientists began to study the efficiency with which a forest, by creating wood, could remove carbon from the air. They realized that, after so many years of focus on their young, experimental plots, they did not yet fully understand the intricate workings of a mature Northwestern forest.

Wind River's old-growth area now hosts the National Ecological Observatory Network (NEON), which gathers data at 81 field sites across the United States and makes it available to anyone interested in tracking how global change is affecting specific ecosystems. On a bright but bitter November morning, I hike with Bible and some NEON employees to the tower that overlooks the forest. (The tower was once part of a construction crane used to hoist gondolas full of scientists up to study the Wind River canopy, but the crane's boom was decommissioned in 2011.) Researchers now use the tower to measure, in exquisite detail, the carbon cycle within Wind River's old growth. Along its length, the tower is outfitted with eight levels of sensors and cameras, a cavity ring-down spectrometer, and something called a sun photometer, part of a gadget accurately described to me as looking like a robotic arm that's going to “shoot down UFOs,” which uses detailed measurements of radiation to determine the nature and quantity of aerosols in the atmosphere. Inside a hut at the bottom of the tower sits a stack of servers to back up the reams of ecological data that are constantly zipping off by satellite to NEON headquarters in Colorado. From there, it's now possible to watch the way carbon dioxide flows differently at the forest floor and the canopy, or to see it temporarily build up in windless groves after trees have stopped photosynthesizing for the night.


We like to imagine that climate change will eventually be solved via grand mobilizations of futuristic technology, and this is surely an impressive one. But as Matt Schroeder, NEON's assistant director of field science, tries to help me understand the maze of wires and machinery, he confesses himself to be more impressed by the engineering wizardry that surrounds the tower. There are scientists racing to invent new technologies that pull carbon from the air, but here, all around him, are billions of needles and leaves that already do it, day in and day out. Through the profound, irreplaceable, utterly ordinary bit of magic that is photosynthesis, trees build themselves from almost nothing, transforming sunlight, carbon dioxide, and water into millions of tons of biomass—approximately half of which is pure carbon, locked safely away from the atmosphere. And old trees, by virtue of their age and size, can hold far more carbon than anybody else.

“Our technology has to be protected in this box,” says Schroeder, gesturing at the hut where the tower's cables and servers and gas cylinders are kept. “Whereas this technology”—he stares up at the towering, once-denigrated old trees and all the hundreds of tons of carbon locked away in their massive trunks—“just works, year-round. It runs on solar power. It creates all of this from thin air.”

Schroeder shakes his head, looking freshly wonderstruck and not like he'd been studying the trees for years. “We have no technology that could do this. The DNA on this landscape has done this.”

A 279-foot-high tower is used to measure carbon cycles within the Wind River canopy.

Photograph: Cody Cobb

The climate scientist Kate Marvel called the 2010s “the decade we knew we were right”—the decade when long-predicted calamities associated with a changing climate began to manifest clearly in our own real world, coming true “with a terrifying rapidity that is no more reassuring because it is easily understood.” From the melting of the Arctic or the bleaching of the Great Barrier Reef to fires and floods and hurricanes and droughts and buckling permafrost, this decade has been both heartbreaking and ominous. We are beginning to experience, faster than any of us hoped we might, how much we have depended on a stable climate, how much we stand to lose now that we are destroying it.

Yet for all the terrifying speed with which the consequences of climate change are now making themselves known, it's important to remember that things could be much worse.


Last year, humans dumped roughly 40 billion tons of carbon dioxide equivalents into the atmosphere, despite knowing that those emissions will create even more warming and planetary havoc. It was a fresh test of our commitment to our survival and well-being, and once again we failed, quite abysmally. Luckily for us, though, this is a test that, simply because of where we live, is always graded on a curve. Only something like half of those 2019 emissions will stay in the atmosphere and continue to make our predicament worse. The rest are obligingly absorbed by forests, like the one at Wind River, as well as by the world's grasslands, wetlands, soils, and oceans. These natural sinks, as they're known, remove carbon from the atmosphere and lock it away, protecting us, if only in part, when we fail to protect ourselves.

Research in Australia and China suggests that certain types of fungi can be added to soil to enhance carbon sequestration by up to 17 percent.

More than a decade ago, while working as an intern for the National Park Service at a small park in Hawaii, I got an eye-opening lesson in just how generous nature's curve can be. Given the assignment to calculate the park's contribution to climate change, I spent weeks dutifully pulling records about electricity use in park buildings and gasoline burned in park trucks, about how much methane we'd generated with our trash and how many hydrofluorocarbons with our refrigeration; I tried to calculate the fuel burned to allow employees to fly to conferences and the barge that delivered our supplies from Honolulu to make its annual trip to our remote location. But when I entered all that information into a program that would calculate our total carbon footprint, I was shocked: It estimated that, poof!, the carbon sequestration provided by the park's forest cover—the scrubby forest where the wild pigs hid, the rich tropical greenery that covered the floors and walls of our deep valleys—canceled out everything else we did. And by a wide margin. Was our forest really so much more important than our emissions?

No and yes. The fundamental predicament of climate change is one of timing and placement. Carbon in our atmosphere has, because of its location, an outsize influence on the temperature of the planet and the ecological chaos we're experiencing as a result. But it's actually a tiny percentage of the carbon that's stored elsewhere on the planet—infinitesimal compared with what's locked in the Earth's crust and mantle and deep ocean, yes, but also just a fraction of the amount of carbon already stored in nature, from forests and algae to peat bogs.

Ken Bible has studied the trees in the Wind River Experimental Forest, a research area in southern Washington state, for more than a quarter century.

Photograph: Cody Cobb

Carbon is said to move in two cycles: There's the slow one—the barely there, eon-scale flux in the carbon stored in the depths of the Earth and ocean—and the fast one, the one that flows at a timescale measurable in the lives of living things. (The two speeds are a bit like the tortoise and the hare, if the hare is running and the tortoise is a long-extinct and forgotten species whose constituent atoms are slowly leaving the world of the living for that of geology.) When we burn fossil fuels, we're polluting our fast world with pieces of the slower one and knocking it out of balance. In the blink of a geological eye, we're returning to the atmosphere huge amounts of carbon that it took nature unfathomable stretches of time to pack safely away.


We know this behavior can't continue. Look at any model of the ways that we might keep Earth from warming more than 2 degrees Celsius (the already dangerous threshold that the Paris agreement was crafted to keep us from crossing), and you will see that there is no path to a stable climate that doesn't include a dramatic reduction in our emissions. We can't keep adding slow carbon to our fast-moving crisis in the living world. There is no confusion about that fact among experts, and it's the reason we talk so much about emissions and the imperative to reduce them.

But there are also important opportunities for change beyond just cutting our use of fossil fuels. All these living things that take in carbon dioxide and turn it into biomass are protecting us through their very existence. When we destroy nature's carbon storage (should we clear-cut all that biomass at Wind River, for instance), we can turn it from a carbon sink into a source, from an ally into yet more fuel for the fires of our era. But what if we were able to help deepen the sinks—to work with nature, to lean into the curve, to help it help us out of a mess of our own making? Nature, too, is an amazing, complex, and remarkably effective technology—our biggest and most overlooked ally in the climate fight.

Scientists work from research stations throughout Wind River forest.

Photograph: Cody Cobb

Once a year, Jim Lutz, a professor of forest ecology at Utah State University, and his students come to Wind River. Within an intricately mapped section of the old forest about the size of 50 football fields, they visit every individual tree and snag and vine over a centimeter in diameter—which is to say, more than 37,000 of them—and record what has died and what has grown, and by how much. This kind of attention to detail is hardly unique among studies at Wind River.

In 2010 it took Lutz and a team roughly 10,000 hours of measuring, tagging, and detailed mapping of trees to set up the plot; the annual forest census takes another 1,500 hours or so. When I ask Lutz what inspired so much effort, he explains that he was pursuing not just a discrete inquiry but “an abiding objective” that would last as long as his career did: a drive to understand the details of how an old-growth forest actually works. When and why do trees die? (“You'd think people would have worked that out by now,” he adds.) When and why do they gain or lose carbon? How does their most basic biology react as the world around them gets hotter or drier? “You have questions that can't be answered except with a large number of trees over a large number of years,” Lutz says.

Photograph: Cody Cobb

Lutz also needed such a vast area to study because he was interested in a relatively rare resident of the forest; to get enough examples of it for his studies to be meaningful, he'd have to cover a lot of land. Lutz's elusive quarry? Thick, old trees like the big Douglas fir that Bible so admired. These days, old-growth forest is itself a rare find, but even within it, the attrition of centuries means that most trees aren't actually that old. As Lutz puts it, “to grow a big tree, you need an old tree, which means a tree has to survive”—not just logging but fires and insects and diseases, and anything else that could have come along during its long life and killed it. Old-growth forest is naturally a complicated mix of ages and sizes and structures. But though truly big trees aren't the most common of the forest's residents, Lutz has learned that their role in its ability to store carbon is as oversized as they are.

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In a 2018 paper looking at 48 different forest plots, including the one in Wind River, he found that the largest 1 percent of trees contain fully half of all the above-ground live biomass, which also means half of all the carbon, since the two are directly correlated. Young trees sequester carbon faster, packing it on in the vigorous growth of their early years, but they can't begin to compete with what large trees have been able to build into their trunks and branches through years and years of maturation. “You can't sequester a lot of carbon without big trees,” Lutz says. “You just can't do it.”

This makes old trees—and even Munger's much-hated dead trees and logs, which can take centuries to rot in the Northwest—not useless but precious. While a single-age stand would lose 1 percent of its carbon storage if it lost 1 percent of its trees, big trees are so important that a 1 percent loss of individuals in an old forest could reduce its carbon by half. And while old forests eventually begin to reach an equilibrium, at which they're not adding a lot more carbon than they're losing through death and decomposition, researchers have found that the old growth in Wind River is still sequestering new carbon each year, adding to the huge amount it already stores. “Even just putting a thin annual growth layer on such a big cylinder is a huge deal,” explains Ben Vierra, who manages NEON's research in the Pacific Northwest. Bible, deep in the grove, says: “This forest is still putting on forest. Quite a bit actually—it could give a young forest a run for its money.”

There has recently been much discussion of tackling climate change by planting lots and lots of trees, something that Lutz is all for—it's still carbon, after all. But he's cautious about how much can really be stored by a lot of willy-nilly new planting, especially if those trees are planted in conditions that will not allow them to thrive and grow old.

Methods for optimizing nature's ability to store carbon are known as natural climate solutions. The word natural, it turns out, is as key as the word solutions—these are strategies that have a lot of potential, but that also work in complex ways that can be difficult for us to understand and re-create. That program I used to figure out the park's carbon footprint in Hawaii back in 2008? Its calculations for carbon storage in landscapes were so new, and still so unsophisticated, that some parks didn't yet bother to report them. (Depending on how I defined the type of forest we had—it was a mix, but in the program I had to choose between “wet tropical” or “dry tropical”—the amount of carbon that the program credited the park with removing from the atmosphere could nearly double.) It's not that forests and other natural areas can't store a lot of carbon—they're currently storing much, much more than is in the atmosphere, including both what's there naturally and what's human-added—it's that carbon moves through them in complicated ways that are hard to measure. How do you account for the natural release of carbon when plants rot? For the widely differing amounts of carbon that different ecosystems hold in soils? For the ways that climate change itself is affecting the way that plants' biology works and how much carbon they can store?



Photograph: Cody Cobb

Some tree-planting schemes envision planting them in places they do not naturally grow, which brings up a host of complications, such as the risk that fire or other local disturbance regimes could destroy new trees and negate any carbon gains, or that covering naturally light-colored or reflective landscapes, such as grasslands, with dark-colored trees could actually warm the Earth faster. Well-meaning tree planters also have to consider that some of the ecosystems the theoretical new plantings would replace are already sequestering sizable amounts of carbon. Forests get lots of attention, but they're hardly our only options for natural carbon sequestration. Intact grasslands, for example, store enormous amounts of carbon in soil, safely away from fire. (However, grasslands are steadily being converted for agriculture.) Peatlands, though they make up only 3 percent of the world's land, sequester more carbon than any other type of terrestrial vegetation. And yet we're constantly draining and drying them to convert the land to other uses, such as oil palm plantations. When Indonesia's desiccated peat swamp forests burned in 2015, the region emitted more carbon each day than did the entire European Union.

Last year, the UN Environment Assembly adopted its first ever resolution to conserve and restore peatlands, the largest natural terrestrial carbon store on Earth.

Natural climate solutions are best approached holistically—a chance to support nature in the work it's already doing. That can mean focusing on the conservation and restoration of ecosystems that we know can hold lots of carbon but which are disappearing rapidly: peatlands and grasslands and forests, but also mangroves, sea grasses, and salt marshes. In agriculture, which can strip soils of much of the carbon they once contained, it can mean using grazing and tilling and cover cropping practices that conserve carbon, or adding more carbon with biochar, a soil amendment made with a kind of charcoal. For forests, easy solutions include focusing on reforestation (planting or simply allowing regrowth in places where trees have been lost) or proforestation (a fancy term for protecting existing forests that might otherwise be cut down) and being thoughtful about afforestation (putting new trees where there were no forests previously). It can even mean managing timberlands to store more carbon. If you cut fewer trees from a stand or cut stands less frequently, you can still produce wood while keeping carbon on the landscape. (In some cases, carefully managed thinning can actually increase carbon sequestration, because it allows remaining trees the chance to grow large.) In the Northwest, Douglas fir plantations are commonly cut every 35 to 40 years, to maximize profits. But it's well known, thanks in part to early studies at Wind River, that letting trees live to 80 or 100, while potentially less lucrative, produces more wood and sequesters more carbon.

Mark Harmon, a forest ecologist at Oregon State University who has been researching carbon storage in forests since the 1970s, tells me that he's lately been hearing more people use carbon sequestration as a justification for doing the opposite: cutting more trees, faster, so you can plant a new generation more quickly. The theory is that carbon is quickly sequestered in plantations and then stored in wood products, rather than wastefully lost to decomposition in older, slow-growing forests. (Sound familiar?)

Harmon sees this as a fundamental—and frustrating—misunderstanding of how carbon works in forests. Young trees take up carbon quickly, sure, but they're starting from a huge carbon deficit if a bunch of older trees had to make way for them. The old-growth section at Wind River holds up to 400,000 kilograms of carbon per hectare and is still adding more. Cut the forest “and it becomes a huge source for a long time,” Bible says.

It's the total storage that matters, explains Harmon: “That's what the atmosphere perceives.” It's also an outcome for which we can choose to manage our timberlands. In the future, we're likely to manage tree plantations for carbon sequestration as well as for wood products, Bible believes, and that's more likely to happen if we finally put a price on carbon. To do otherwise would be to turn our backs on an offer of help when we need it most.


There's still a lot we don't know about how the natural systems that sequester so much of our carbon operate, or how they will respond as the world changes around them. Some of these changes may be significant. More carbon dioxide in the atmosphere, for example, means that some trees may sequester carbon faster, but warming also leads to problems like drought stress and increased wildfire, which mean more carbon escapes. When a strong El Niño hit the Pacific Ocean in 2015, nature stored only about 44 percent of that year's human emissions, compared with 66 percent during a colder La Niña in 2011.

But we're learning more all the time—at Wind River and elsewhere—about how nature absorbs carbon, how to allow it to absorb more, and how meaningful that help could be. One recent study suggested a suite of land management changes—restoration of degraded forests, wetlands, and grasslands; carbon-sensitive agriculture; better management of timberlands—that if enacted in the US could quickly offset a fifth of our current emissions. Another found that, globally, natural climate solutions could provide as much as 37 percent of the cost-effective carbon mitigation necessary between now and 2030 to keep warming from exceeding 2 degrees Celsius.

“We have to acknowledge,” says Harmon, “that natural systems have the capacity to repair things and to help us. We have to take more advantage of them, not less.”

Photograph: Cody Cobb

Before we leave Wind River, Bible wants to show me another part of the experimental forest. We turn our backs on the giants and follow a slight path around a small wetland and through a grove of alder trees, arriving in a section of forest that has been managed quite differently.

It feels as if I hadn't quite seen the old growth until we walk away from it. It isn't just that this other, much younger section of forest has smaller trees; it also has much less moss, much more light, a totally different understory. Though only a few hundred yards away, it feels unfamiliar, like a different forest type altogether. It's a cliché to say that an old-growth grove feels like a cathedral, but after leaving it, the younger forest makes me think of pictures I've seen of bombed-out churches—sacred spaces suddenly opened to the world, unaccustomed sunlight streaming vulgarly in. “When the wind and dry come through here,” says Bible, “it just cuts through like a comb.”


This young stand is home to many more trees, per hectare, than the older one we've just left, yet researchers have found that it holds less than a quarter of the carbon. “If we were standing here 100 years ago”—before the forest was removed—“it was exactly like where we just were,” says Bible. “It's going to take a really long time to get back to that stage.” But he hopes that the foresters of the future will be able to help speed the process.

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Munger and his contemporaries would likely be surprised to learn that today's foresters are preoccupied with finding ways to promote the very features that they derided in old growth—dead wood, trees of a variety of sizes and ages, decomposition, large quantities of biomass just standing or lying around—and seeking to re-create them even in the young tree plantations that their predecessors prized for not having those things. New versions of the old spacing research are showing that with targeted thinning and management, you can create old-growth features even in homogenous commercial forests, allowing space for trees to grow to huge sizes in the future. Outside of the old-growth reserve, Bible says, much of the future of experiments at Wind River lies in studying ways to help forests maximize not profit but carbon storage. Munger's “decadent” forests and murderous snags “were systematically removed in the 20th century,” write Herring and Greene. “Now they are being systematically returned in the 21st century.”

It has occurred to Lutz that his decision to study old-growth forests may seem a bit odd: Why bother to become an expert in a world that is all but gone? But he likes to remind people that the condition of our forests is a choice, a decision that's now more social than natural. In the future we will have only the natural places that we choose to have, only the ones that we value enough to protect and restore and nurture. One day, he says, if people decide they want more of these big, old, complicated forests in the world, “then I can help.” And that forest, in turn, can help us.

BROOKE JARVIS (@brookejarvis) lives in Seattle. She's working on a book about insects. Her last story for WIRED, about online harassment, was in issue 25.12

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