Inside the quest to engineer climate-saving “super trees”

Fifty-three million years ago, the Earth was much warmer than it is today. Even the Arctic Ocean was a balmy 50 °F—an almost-tropical environment that looked something like Florida, complete with swaying palm trees and roving crocodiles. 

Then the world seemed to pivot. The amount of carbon in the atmosphere plummeted, and things began to cool toward today’s “icehouse” conditions, meaning that glaciers can persist well beyond the poles. 

What caused the change was, for decades, unclear. Eventually, scientists drilling into Arctic mud discovered a potential clue: a layer of fossilized freshwater ferns up to 20 meters thick. The site suggested that the Arctic Ocean may have been covered for a time in vast mats of small-leaved aquatic Azolla ferns. Azollas are among the fastest-growing plants on the planet, and the scientists theorized that if such ferns coated the ocean, they could have consumed huge quantities of carbon, helping scrub the atmosphere of greenhouse gasses and thereby cooling the planet.

Patrick Mellor, paleobiologist and chief technology officer of the biotech startup Living Carbon, sees a lesson in the story about these diminutive ferns: photosynthesis can save the world. Certain fluke conditions seem to have helped the Azollas along, though. The arrangement of continental plates at the time meant the Arctic Ocean was mostly enclosed, like a massive lake, which allowed a thin layer of fresh river water to collect atop it, creating the kind of conditions the ferns needed. And crucially, when each generation of ferns died, they settled into saltier water that helped inhibit decay, keeping microbes from releasing the ferns’ stored carbon back into the atmosphere.

Mellor says we can’t wait millions of years for the right conditions to return. If we want plants to save the climate again, we have to prod them along. “How do we engineer an anthropogenic Azolla event?” he says. “That’s what I wanted to do.”

At Living Carbon, Mellor is trying to design trees that grow faster and grab more carbon than their natural peers, as well as trees that resist rot, keeping that carbon out of the atmosphere. In February, less than four years after he co-founded it, the company made headlines by planting its first “photosynthesis-enhanced” poplar trees in a strip of bottomland forests in Georgia. 

This is a breakthrough, clearly: it’s the first forest in the United States that contains genetically engineered trees. But there’s still much we don’t know. How will these trees affect the rest of the forest? How far will their genes spread? And how good are they, really, at pulling more carbon from the atmosphere?

Living Carbon has already sold carbon credits for its new forest to individual consumers interested in paying to offset some of their own greenhouse gas emissions. They’re working with larger companies, to which they plan to deliver credits in the coming years. But academics who study forest health and tree photosynthesis question whether the trees will be able to absorb as much carbon as advertised. 

Even Steve Strauss, a prominent tree geneticist at Oregon State University who briefly served on Living Carbon’s scientific advisory board and is conducting field trials for the company, told me in the days before the first planting that the trees might not grow as well as natural poplars. “I’m kind of a little conflicted,” he said, “that they’re going ahead with this—all the public relations and the financing—on something that we don’t know if it works.”

Roots of an idea

In photosynthesis, plants pull carbon dioxide out of the atmosphere and use the energy from sunlight to turn it into sugars. They burn some sugars for energy and use some to build more plant matter—a store of carbon.

A research group based at the University of Illinois Urbana-Champaign supercharged this process, publishing their results in early 2019. They solved a problem presented by RuBisCO, an enzyme many plants use to grab atmospheric carbon. Sometimes the enzyme accidentally bonds with oxygen, a mistake that yields something akin to a toxin. As the plant processes this material, it must burn some of its sugars, thereby releasing carbon back to the sky. A quarter or more of the carbon absorbed by plants can be wasted through this process, known as photorespiration.

The researchers inserted genes into tobacco plants that helped them turn the toxin-like material into more sugar. These genetically tweaked plants grew 25% larger than controls.

The breakthrough offered good news for the world’s natural landscapes: if this genetic pathway yields more productive crops, we’ll need less farmland, sparing forests and grasslands that otherwise would have to be cleared. As for the plants’ ability to remove atmospheric carbon over the long term, the new trick doesn’t help much. Each year, much of the carbon in a crop plant’s biomass gets returned to the atmosphere after it’s consumed, whether by microbes or fungi or human beings. 

Still, the result caught the attention of Maddie Hall, a veteran of several Silicon Valley startups who was interested in launching her own carbon-capture venture. Hall reached out to Donald Ort, the biologist who’d led the project, and learned that the same tweaks might work in trees—which stay in the ground long enough to serve as a potential climate solution.

Late in 2019, Hall settled on the name for her startup: Living Carbon. Not long afterward, she met Mellor at a climate conference. Mellor was then serving as a fellow with the Foresight Institute, a think tank focused on ambitious future technologies, and had become interested in plants like Pycnandra acuminata. This tree, native to the South Pacific islands of New Caledonia, pulls huge quantities of nickel out of the soil. That’s likely a defense against insects, but as nickel has natural antifungal properties, the resulting wood is less prone to decay. Mellor figured if he could transfer the correct gene into more species, he could engineer his Azolla event.

When Mellor and Hall met, they realized their projects were complementary: put the genes together and you’d get a truly super tree, faster-growing and capable of more permanent carbon storage. Hall tapped various contacts in Silicon Valley to collect $15 million in seed money, and a company was born.

In some ways, Living Carbon’s goal was simple, at least when it came to photosynthesis: take known genetic pathways and place them in new species, a process that’s been conducted with plants for nearly 40 years. “There’s a lot of mystification of this stuff, but really it’s just a set of laboratory techniques,” Mellor says. 

Since neither Mellor nor Hall had substantial experience with genetic transformation, they enlisted outside scientists to do some of the early work. The company focused on replicating Ort’s enhanced-photosynthesis pathway in trees, targeting two species: poplars, which are popular with researchers because of their well-studied genome, and loblolly pines, a common timber species. By 2020, the tweaked trees had been planted in a grow room, a converted recording studio in San Francisco. The enhanced poplars quickly showed results even more promising than Ort’s tobacco plants. In early 2022, Living Carbon’s team posted a paper on the preprint server bioRxiv claiming that the best-performing tree showed 53% more above-ground biomass than controls after five months. (A peer-reviewed version of the paper appeared in the journal Forests in April.) 

Through the loophole

Plant genetics research can be a long scientific slog. What works in a greenhouse, where conditions can be carefully controlled, may not work as well in outdoor settings, where the amounts of light and nutrients a plant receives vary. The standard next step after a successful greenhouse result is a field trial, which allows scientists to observe how genetically engineered (GE) plants might fare outside without actually setting them fully loose.

US Department of Agriculture (USDA) regulations for GE field trials aim to minimize “gene drift,” in which the novel genes might spread into the wild. Permits require that biotech trees be planted far from species with which they could potentially reproduce, and in some cases the rules dictate that any flowers be removed. Researchers must check the field site after the study to ensure no trace of the GE plants remain.

Before planting trees in Georgia, Living Carbon launched its own field trials. The company hired Oregon State’s Strauss, who had given Living Carbon the poplar clone it had used in its gene transfer experiments. In the summer of 2021, Strauss planted the redesigned trees in a section of the university’s property in Oregon.

Strauss has been conducting such field trials for decades, often for commercial companies trying to create better timber technologies. It’s a process that requires patience, he says: most companies want to wait until a “half rotation,” or midway to harvest age, before determining whether a field trial’s results are promising enough to move forward with a commercial planting. Living Carbon’s trees may never be harvested, which makes setting a cutoff date difficult. But when we spoke in February, less than two years into the field trial and just before Living Carbon’s initial planting, Strauss said it was too early to determine whether the company’s trees would perform as they had in the greenhouse. “There could be a negative,” he said. “We don’t know.” 

looking up at a tree that is poking up through clouds


Strauss has been critical of the US regulatory requirements for field trials, which he sees as costly, a barrier that scares off many academics. The framework behind its rules emerged in the 1980s when, rather than wait on the slow grind of the legislative process, the Reagan administration adapted existing laws to fit new genetic technologies. For the USDA, the chosen tool was its broad authority over “plant pests,” a term meant to describe anything that might injure a plant—whether an overly hungry animal, a parasitic bacterium, or a weed that might outcompete a crop.

At the time, gene transfer in plants was almost entirely accomplished with the help of Agrobacterium tumefaciens. This microbe attacks plants by inserting its own genes, much like a virus. But scientists found they could convince the bacterium to deliver whatever snippets of code they desired. Since Agrobacterium itself is considered a plant pest, the USDA decided it had the authority to regulate the interstate movement and environmental release of any plant that had had its genes transformed by the microbe. This meant nearly comprehensive regulation of GE plants. 

In 1987, just one year after the USDA established its policy, a team of Cornell researchers announced the successful use of what’s become known as a “gene gun”—or, less colorfully, “biolistics”—in which bits of DNA are literally blasted into a plant cell, carried by high-velocity particles. No plant pest was involved. This created a loophole in the system, a way to produce GE plants that the current laws did not cover.

Since then, more than 100 GE plants, mostly modified crop plants, have thus escaped the USDA’s regulatory scrutiny.

Agrobacterium remains a common method of gene transfer, and it’s how Living Carbon produced the trees discussed in its paper. But Mellor knew going to market with trees considered potential plant pests “would be a long and depressing path,” he says, one with tests and studies and pauses to collect public comment. “It would take years, and we just wouldn’t survive.”

Once Living Carbon saw that its trees had promise, it dove through the loophole, creating new versions of its enhanced trees via biolistics. In formal letters to the USDA the company explained what it was doing; the agency replied that, because the resulting trees had not been exposed to and did not contain genes from a plant pest, they were not subject to regulations.

Other federal agencies also have authority over biotechnology. The Environmental Protection Agency regulates biotech plants that produce their own pesticides, and the Food and Drug Administration examines anything humans might consume. Living Carbon’s trees do not fit into either of these categories, so they could be planted without any further formal studies.

A year after Living Carbon announced its greenhouse results—before the data from the field trial had any meaning, according to Strauss—the company sent a team to Georgia to plant the first batch of seedlings outside strictly controlled fields. Mellor indicated that this would double as one more study site, where the trees would be measured to estimate the rate of biomass accumulation. The company could make an effort to start soaking up carbon even as it was verifying the efficacy of its trees.

Out in the wild

Experiments with genetically modified trees have historically evoked a strong response from anti-GE activists. In 2001, around 800 specimens growing in Strauss’s test plots at Oregon State University were chopped down or otherwise mutilated. 

In 2015, in response to the news that the biotech firm ArborGen had created a loblolly pine with “increased wood density,” protesters descended on the company’s South Carolina headquarters. (The company had taken advantage of the same loophole as Living Carbon; ArborGen has said the pine was never commercially planted.) But after the New York Times wrote about Living Carbon’s first planting in February, there were no notable protests.

One reason could be that the risk is far from clear-cut. Several forest ecologists I spoke to indicated that trees that grow substantially faster than other species could outcompete rivals, potentially making Living Carbon’s “super tree” a weed. None of these scientists, though, seemed particularly worried about that happening.

“I think it’d be difficult to on purpose make a tree that was a weed—that was able to invade and take over a forest,” said Sean McMahon, a forest ecologist with the Smithsonian Tropical Research Institute. “I think it’d be impossible by accident to do it. I’m really not worried about a tree that takes over the world. I just think you’re going to break [the tree].” 

He pointed out that the timber industry has been working with scientists for decades, hoping to engineer fast-growing trees. “This is a billion-dollar industry, and if they could make trees grow to harvest in five years, they would,” he said. But there tend to be tradeoffs. A faster-growing tree, for example, might be more vulnerable to pests. 

The other reason for the quiet reception of these trees may be climate change: in a ravaged world, people may be more willing to tolerate risk. Keolu Fox, a geneticist at the University of California San Diego, is a co-director of science at Lab to Land, a nonprofit that is studying the potential for biotechnology to accelerate conservation goals on threatened lands, particularly in California. “We’re now talking about editing natural lands—that’s desperation,” Fox says. He thinks this desperation is appropriate, given the state of the climate crisis, though he’s not entirely convinced by Living Carbon’s approach.

Mellor suggests that gene drift should not be a problem: Living Carbon is planting only female trees, so the poplars don’t produce any pollen. That will not prevent wild-growing male trees from fertilizing the transgenic poplars, though the amount of resulting gene drift will likely be small and easily contained, Living Carbon says, especially given the company’s ability to avoid planting its trees near species that could fertilize them. But Mellor says he prefers to focus on other issues. Yes, some companies, like Monsanto, have used transgenic crops in exploitative ways, but that doesn’t mean transgenic technologies are inherently bad, he says. “Purity” is a silly standard, he says, and by trying to keep plants pure we’re missing the chance for needed innovations.

Living Carbon’s poplars seem to grow faster and survive droughts better than their natural counterparts, Mellor says. The rest of their genes match. “So, if, say, that competitively replaces the non-photosynthesis-enhanced version, is that a problem?” he asks. “And what kind of a problem is that? That’s the question now.” 

Plant or pest?

In 2019, before Living Carbon was formed, the USDA announced its intention to update its regulatory approach to transgenic plants. The new rules went into effect in August 2020, just after Living Carbon submitted letters seeking exemption for its trees; the letters were reviewed and the trees were grandfathered in under the old rules.

Any further biotechnology the company develops will be analyzed using the new approach, which focuses on what traits are inserted into plants rather than how they get there. There are still ways to avoid scrutiny: products whose genetic modification could be accomplished through conventional breeding, for example, are not subject to regulation—a loophole watchdog groups find problematic. But according to USDA spokespeople, Living Carbon’s core technology—fast-growing trees, produced through genetic insertion—does not appear to qualify for such exemptions. If Living Carbon wants to make even a slight genetic tweak to its trees, the new product will require further examination.

The USDA’s first step is to determine whether there is “a plausible pathway to increased plant pest risk.” If the answer is yes, the company will need permits to move or plant such trees until the USDA can complete a full regulatory review. 

Because the agency has not yet reviewed a tree with enhanced photosynthesis, officials declined to comment on whether the trait might constitute a pest risk. Even if it does not, the process might miss other risks: a 2019 report from the National Academies of Sciences, Engineering, and Medicine pointed out that pest risk is a narrow metric that does not capture all of the potential threats to forest health. 

Nor does the USDA process offer a seal of approval suggesting the trees will actually work.

“One of the things that concerns me is [Living Carbon is] just focusing on carbon acquisition,” says Marjorie Lundgren, a researcher at Lancaster University in the UK who has studied tree species with natural adaptations leading to increased photosynthetic efficiency. She notes that trees need more than just carbon and sunlight to grow; they need water and nitrogen, too. “The reason they have such a high growth rate is because in the lab, you can just super-baby them—you can give them lots of water and fertilizer and everything they need,” she says. “Unless you put resources in, which is time and money, and not great for the environment, either, then you’re not going to have those same outcomes.” 

Living Carbon’s paper acknowledges as much, citing nitrogen as a potential challenge and noting that how the trees move carbon may become a limiting factor. The extra sugars produced through what the company calls “enhanced photosynthesis” must be transported to the right places, something trees haven’t typically evolved to do. 

The final, peer-reviewed version of the paper was amended to note the need to compare the grow-room results with field trials. And, as it happened, in April—the month the paper was published—Strauss sent Living Carbon an annual report with exciting news. He had noted statistically significant differences in height and drought tolerance between Living Carbon’s trees and the controls. He also found “nearly” significant differences in volume and diameter for some lines of engineered trees. 

Capturing the carbon

Living Carbon seems aware of the general public distrust of genetic technologies. Hall, the CEO, has said the company does not want to be “the Monsanto of trees” and is registered as a public benefit corporation. That allows it to decline ethically dubious projects without worrying about being sued by shareholders for passing up profits.

The company advertises its focus on “restoring land that has been degraded or is underperforming.” On its website, the pitch to potential carbon-credit buyers emphasizes that the tree-planting projects serve to restore ecosystems. 

One hope is that Mellor’s metal-accumulating trees will be able to restore soils at abandoned mining sites. Brenda Jo McManama, a campaign organizer with the Indigenous Environmental Network, lives amid such landscapes in West Virginia. She has been fighting GE trees for almost a decade and remains opposed to the technology, but she understands the appeal of such remediating trees. One key problem: they remain experimental. 

McManama notes, too, that landowners are allowed to harvest the wood from Living Carbon’s trees. This is not a problem for the climate—lumber still stores carbon—but it undercuts the idea that this is all about ecosystems. “Under their breath, it’s like, ‘Yeah, this will be a tree plantation,’” she says.

The initial planting site in Georgia, for example, belongs to Vince Stanley, whose family owns tens of thousands of acres of timber in the area. Stanley told the New York Times that the appeal of the trees was that he would be able to harvest them sooner than traditional trees.

Living Carbon contests the idea that it is creating “plantations,” which by definition would mean monocultures. But it has planted 12 different species on Stanley’s land. The company indicated that it is “interested” in partnering with timber companies; as Hall has noted, the top 10 in the US each own at least 1 million acres. But the Stanley site in Georgia is currently the only project that is technically classified as “improved forestry management.” (And even there, the company notes, the existing forest was regenerating very slowly due to wet conditions.)

Living Carbon funds its plantings—and makes its profits—by selling credits for the extra carbon the trees absorb. Currently, the company is offering “pre-purchases,” in which companies make a commitment to buy a future credit, paying a small portion of the fee up front to help Living Carbon survive long enough to deliver results.

The company has found that these buyers are more interested in projects with ecosystem benefits, which is why the first project, in Georgia, has become an outlier. There has been a subsequent planting in Ohio; this and all currently planned plantings are not near sawmills or in active timber harvesting regions. Thus, the company does not expect those trees to be harvested.

Wherever they plant trees—whether atop an old minefield or in a timber-producing forest—Living Carbon will pay the landowner an annual per-acre fee and cover the cost of plant site preparation and planting. At the end of the contract, after 30 or 40 years, the landowner can do whatever they want with the trees. If the trees grow as well as is hoped, Living Carbon assumes that even on timber land, their size would mean they’d be turned into “long-duration wood products,” like lumber for construction, rather than shredded to make pulp or paper.

Until recently, Living Carbon was also selling small-scale credits to individual consumers. When we spoke in February, Mellor pointed me toward Patch, a software company with a carbon-credit sales platform. The Georgia project was marketed there as “biotech-enhanced reforestation.” The credits were offered as a monthly subscription, at a price of $40 per metric ton of carbon removed. 

When I pressed Mellor for details about how the company calculated this price, given the lack of any solid data on the trees’ performance, he told me something the company had not  acknowledged in any public-facing documentation: 95% of the saplings at the Georgia site were not photosynthesis-enhanced. The GE poplar trees were planted in randomized experimental plots, with controls for comparison, and contribute only a small amount to the site’s projected carbon savings. Despite the advertising, then, customers were really paying for a traditional reforestation project with a small experiment tucked inside. 

A spokesperson for Living Carbon clarified that this planting makeup was dictated by the standards of the American Carbon Registry, the organization that independently certified the resulting credits, and that subsequent plantings have included a higher proportion of enhanced trees. By partnering with a new credit registry, Living Carbon hopes its 2024 plantings will be closer to 50% photosynthesis-enhanced.

That carbon credits can be offered for the Georgia site at all serves as a reminder: old-fashioned trees, without any new genes, already serve as a viable carbon drawdown technology. “There’s 80,000 species of trees in the world. Maybe you don’t have to throw nickel in them and CRISPR them,” said McMahon, of the Smithsonian Tropical Research Institute. “Maybe just find the ones that actually grow fast [and] store carbon a long time.” Or, he added, pass regulation to protect existing forests, which he said could help the climate more than even a massive adoption of high-tech trees. 

Grayson Badgley, an ecologist at the nonprofit CarbonPlan, notes that the cost of the credits on Patch was on the high side for a reforestation project. CarbonPlan examines the efficacy of various carbon removal strategies, a necessary intervention given that carbon markets are ripe for abuse. Several recent investigations have shown that offset projects can dramatically inflate their benefits. One major regulatory group, the Integrity Council for the Voluntary Carbon Market, recently announced a new set of rules, and Verra, a US nonprofit that certifies offset projects, also plans to phase out its old approach to forestry projects.

Given the increasingly shaky reputation of carbon markets, Badgley finds Living Carbon’s lack of transparency troubling. “People should know exactly what they’re buying when they plug in their credit card number,” he says. 

Living Carbon says it began phasing out direct-to-consumer sales in late 2022, and that the final transaction was made late February, not long after the Georgia planting. (In total, subscribers funded 600 trees—a small portion of the 8,900 transgenic trees Living Carbon had planted as of late May.) I purchased a credit for research purposes in early February; as of March 1, when I canceled the subscription, I had received no details clarifying the makeup of the Georgia planting, nor any updates noting that the program was ending. I was also struck by the fact that in February, before Strauss delivered his data, Living Carbon was already touting field trial results on its website, ones that were even more impressive than its grow-room results. After I inquired about the source of these figures, the company removed them from the website.

The company says it’s fully transparent with the large-scale buyers who make up the core of its business strategy. What seemed to me like problematic embellishments and elisions were, according to spokespeople, the growing pains of a young startup with an evolving approach that is still learning how to communicate about its work. 

They also pointed out that many of the problems with forestry carbon credits come from the projects meant to protect forests against logging. Such credits are granted based on a counterfactual: how many trees would be destroyed in the absence of protection? That’s impossible to know with any precision. How much extra carbon Living Carbon’s trees absorb will be measured much more clearly. And if the trees don’t work, Living Carbon won’t be able to deliver its promised credits or get paid for them. “The risk that in the end [the trees] won’t deliver the amount of carbon that’s expected is on us—it’s not on the climate,” a company spokesperson said.

Pines and pollen

Living Carbon has bigger plans in the works (which will likely need to undergo USDA scrutiny). Mellor hopes the photosynthesis-enhanced loblolly pines will be ready for deployment within two years, which would open opportunities for more collaboration with timber companies. Experiments with metal-accumulating trees are underway, with funding from the US Department of Energy. Last year, the company launched a longer-term project that aims to engineer algae to produce sporopollenin, a biopolymer that coats spores and pollen and can last 100 times longer than other biological materials—and maybe longer than that, the company says. This could create a secure, long-term way to store carbon.

Living Carbon is not alone in this field. Lab to Land, the nonprofit targeting California ecosystems, is considering how carbon markets might drive demand for deep-rooted grasses that store carbon. But Lab to Land is moving far more slowly than Living Carbon—it’s at least a decade away from the deployment of any biotechnology, one of the co-directors of science told me—and, as it progresses, it is building multiple councils to consider the ethics of biotechnology.

A Living Carbon spokesperson suggested that “every scientist is in a way a bioethicist,” and that the company operates with careful morals. As a startup, Living Carbon can’t afford to dither—it needs to make a profit—and Hall says the planet can’t afford to dither, either. To solve climate change, we have to start trying potential technology now. She sees the current plantings as further studies that will help the company and the world understand these trees. 

Even with the new data, Steve Strauss remained circumspect about the trees’ long-term prospects. Living Carbon has only provided enough funding for the Oregon field tests to extend just beyond the current growing season; Strauss indicated that were this his company, he’d “want more time.”

Still, Strauss was the one academic scientist I spoke to who seemed enthused about Living Carbon’s plantings. He said they’d made a breakthrough, though one that is less scientific than social—a first step beyond the confines of test-plot fields. As a longtime proponent of genetic engineering, he thinks research into biotechnical solutions to climate change has been stalled for too long. The climate crisis is growing worse. Now someone is pushing forward. “Maybe this isn’t the ideal thing,” he told me when we first spoke in February. “And maybe they’re pushing this one product too hard, too fast. But I’m sort of glad it’s happening.”

Boyce Upholt is a writer based in New Orleans.

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