Science

Planting Trees Won’t Stop Climate Change

Not only are planted trees not the carbon sinks you want, but tree planting frequently ends up doing more harm than good.

Gloved hands plant a sapling in soil.
Михаил Руденко/iStock/Getty Images Plus

Humans have long believed that planting trees, any kind of tree, anywhere, is good, something Mother Nature cries out for, something that might even solve our climate crisis. Tree-planting initiatives proliferate: the Bonn Challenge, Trees for the Future, Trees Forever, the 10 Billion Tree Tsunami, Plant a Billion Trees, 8 Billion Trees, the Trillion Tree Campaign, the One Trillion Trees Initiative, to mention just a few.

The passion for planting trees comes partly from the fact that, in some places, they sequester carbon. This has been broadly interpreted to mean that festooning the Earth with trees will solve the problem of climate change, which is why tree-planting programs are so popular with carbon polluters seeking to avoid cleanup costs. President Donald Trump, for example, instantly embraced the One Trillion Tree Initiative launched in January by the World Economic Forum, pledged U.S. participation, and then gushed about it in his State of the Union address: “To protect the environment, days ago, I announced that the United States will join the One Trillion Tree Initiative, an ambitious effort to bring together government and the private sector to plant new trees in America and around the world.”

Planting trees can be beneficial, especially in countries where predatory logging and other land abuse has destroyed soil stability and deprived people of shade, clean water, fish, and fruit. But such initiatives are the exception. Mass plantings are apt to do more harm than good. And it’s nearly impossible to distinguish decent projects from bad ones.

First there is the problem of duplicity, not unusual among tree-planting outfits. Consider Plant for the Planet, the organization behind the Trillion Tree Campaign. In March 2019, the German newspaper Die Zeit revealed that the group’s website was rife with untruths. For example, one person—a “Valf F.” from France—was reported to have single-handedly planted 682 million trees.

The other, larger problem is the ecological havoc tree planters can wreak if they are not careful. Few divulge what species they plant. Fewer still commit to planting only native species. Those who do commit are apt to plant monocultures, which are nearly worthless to wildlife and vulnerable to disease, insects, and wind. Forests are complex machines with millions of meshing parts. You can’t plant a forest; you can only plant a plantation.

Trees planted in wrong places, particularly places that are naturally treeless, do more harm than good and trash native ecosystems. Prairies, for example, provide important habitat for all manner of wildlife. But ever since European settlement, Americans have been destroying them with trees. When J. Sterling Morton moved to Nebraska from Michigan in 1854, he decided that Mother Nature had gotten it all wrong. In due course he called forth “a grand army of husbandmen … to battle against the timberless prairies,” and on April 10, 1872, established the first Arbor Day. Twenty-four hours later, Nebraskan prairies had been degraded by roughly 1 million planted trees.

A field of grass
U.S. Fish and Wildlife Service

Tree planting, especially on Arbor Day, became a national obsession. In celebration of the 100th anniversary of Arbor Day, the Nebraska-based Arbor Day Foundation was formed. It hasn’t deviated far from Morton’s mindset. Join and you can receive 10 free Colorado blue spruce seedlings with instructions on how to plant them. This would be fine if you live in the central or southern Rockies. But everywhere else, these trees are aliens.

Illustrating the extent of our current tree-planting craze is the recent marketing of biodegradable coffee cups impregnated with tree seeds. Not only do they encourage littering, but they guarantee that wrong trees will be planted in wrong places.

But such slapdash planting is an American tradition. In 1876, possibly inspired by Arbor Day, a man named Ellwood Cooper sought to improve his 2,000-acre, mostly treeless ranch near Santa Barbara, California, with 50,000 eucalyptus seedlings. They shot up 40 feet in just three years, an unheard-of growth rate for which they became known as “miracle trees.” Eucalyptus trees are not native to California.

Shortly thereafter, the University of California and the state Department of Forestry distributed free eucs for everyone to plant. Prairies, chaparral, and cutover forestland were jammed full of these aliens. One hundred years after the first Arbor Day, 271,800 acres of eucalyptus had been planted in the U.S., 197,700 of them in California.

In a grassland, a few of trees on fire and bellowing smoke into the sky can be seen
U.S. Fish and Wildlife Service

When I inserted my arm into euc leaf and bark litter in Bolinas, California, I couldn’t touch the bottom. That’s because the microbes and insects that eat it are in Australia, not California. Native plant communities can’t survive in these plantations because eucs kill competition with their own herbicide, creating what botanists call “eucalyptus desolation.” Eucs evolved with fire and prosper from it. Their tops don’t just burn; they explode. Living near them is like living beside a gasoline refinery staffed by chain smokers.

But eucs remain popular in California. They’re still being planted. And agencies seeking to protect the public and recover native ecosystems by razing eucs inevitably face the fury of eucalyptus lovers who have, for example, accused them of being “plant Nazis.”

According to a mantra heard for more than three decades, trees are good, even if they disrupt native ecosystems, because they can serve as carbon sinks. In 1988, the then–113-year-old American Forestry Association (now American Forests) initiated its Global ReLeaf campaign under the shibboleth “Plant a tree, cool the globe.” Too bad it’s not that simple. A study led by the Lawrence Livermore National Laboratory concludes that any carbon sequestration benefit from trees planted much north of Florida is more than offset because solar heat absorbed and retained by the trees makes the climate warmer.

The notion that any significant percent of the carbon humanity spews can be sucked up by planted trees is a pipe dream. But it got rocket boosters in July, when Zurich’s Crowther Lab published a paper, in Science, proclaiming that planting a trillion trees could store “25 percent of the current atmospheric carbon pool.” That assertion is ridiculous, because planting a trillion trees, one-third of all trees currently on earth, is impossible. Even a start would require the destruction of grasslands (prairies, rangelands, and savannas) that reflect rather than absorb solar heat and that, with current climate conditions, are better carbon sinks than natural forests, let alone plantations. Also, unlike trees, grasslands store most of their carbon underground, so it’s not released when they burn.

The Crowther paper horrified climate scientists and ecologists, 46 of whom wrote a rebuttal, explaining that planting trees in the wrong places would exacerbate global warming, create fire hazards, and devastate wildlife. They rebuked the authors for “suggesting grasslands and savannas as potential sites for restoration using trees” and for overestimating by a factor of 5 “potential for new trees to capture carbon.”

Tree plantations are already destroying natural areas that are far more efficient at storing carbon—wetlands, for example. When organic detritus is trapped underwater it can’t release carbon because there’s no oxygen for decomposition. Carbon sequestration efficiency of coastal wetlands (marshes, mangroves and seagrasses) actually increases with global warming because, as sea levels rise, more and more storage space for detritus becomes available.

Ill-conceived tree plantings can dewater wetlands. Consider the yet-to-be-launched initiative to plant 2.4 billion trees in India’s Cauvery River basin, which is the brainchild of the Isha Foundation, based in Coimbatore, India. Leonardo DiCaprio, whose foundation is a major backer, received a letter in September from 95 of India’s environmental and public interest groups that cited litigation against the plan. It read in part: “Biodiversity, forests, grasslands and the massive deltaic region that this river nurtures would be devastated. … It appears to be a programme that presents, rather simplistically, that the river can be saved by planting trees on banks of her streams, rivulets, tributaries and the floodplains … a method that promotes a monoculturist paradigm of landscape restoration which people of India have rejected long ago.” The Isha Foundation dismissed the letter as an attempt “to gain publicity.”

Similarly, in September Ireland committed to planting 440 million trees as part of its Climate Action Plan. Many of them will be commercially valuable Sitka spruce from North America’s Pacific Northwest. When they’re harvested, sequestered carbon will spew back into the atmosphere. Meanwhile, these aliens will be drying up wetlands, increasing global warming by absorbing and retaining solar heat, and, as the Irish Wildlife Trust warns, speeding extirpation of fish and wildlife (ongoing because of previous alien-tree plantings).

The notion that tree planting is an elixir for what ails the earth is as popular with polluters as it is with nations, a fact that spawned the “carbon offset industry.” Polluters hire third parties—often unseen, uninterviewed, and in other countries—to plant any kind of trees, anywhere. For instance, in November, EasyJet announced that it will spend $33 million for tree planting and other carbon-reduction schemes, supposedly rendering itself the first airline to offset all its CO2 pollution. In February Delta Air Lines pledged to zero out its carbon emissions by spending $1 billion over the next decade. While it was vague on how this will be accomplished, tree planting is reportedly part of the strategy.

Carbon offsetting has been likened to “indulgences,” the forgiveness notes hawked by the pre-Reformation Catholic Church—go and sin no more unless, of course, you pay us off again for future sins. Also, hired tree planters frequently charge for trees that would be planted anyway or pocket the money and plant nothing.

According to Kevin Anderson, professor of energy and climate change at the U.K.’s University of Manchester, the entire carbon offset industry is a “scam.” In 2019, after two decades of carbon offsetting, CO2 levels peaked at the highest levels in recorded history.

Carbon offsetting might work if polluters paid parties to protect existing forests and maybe also restore wetlands and grasslands by cutting planted and invading trees. On 400,000 acres in Montana, the American Prairie Reserve recovers native prairie by razing alien Russian olive and Chinese locust trees and reseeding bare, abandoned cropland with a native prairie mix.

The same restoration is done by the U.S. Fish and Wildlife Service at national wildlife refuges such as Bowdoin and Medicine Lake, both in Montana. “I have old photos showing settlers out on the prairie, and there’s not a single tree in the background,” says Neil Shook, who manages these two refuges. “Now the same places are littered with trees. By cutting trees we’re seeing increases in prairie vegetation and grassland songbirds. But people are still planting Russian olives. Right outside our boundaries you can see what will happen if we don’t cut. That private land is just full of trees.”

At top, a view of a trail leading into a forest is seen. At bottom, the same field is seen with a large portion of the trees cut down.
U.S. Fish and Wildlife Service

Thanks to aggressive tree removal by the USFWS at Union Slough National Wildlife Refuge in Iowa, prairie-dependent plants, birds, and mammals are surging back. For years, tree lovers have railed at Union Slough managers, accusing them of such malfeasance as “arboricide.” But as the refuge presses on the noise fades.

Reform seems to take two steps back and three forward. “We’re pushing hard for San Francisco to plant native trees that will bring wildlife into the city and link it with our parks,” remarks Jacob Sigg of the California Native Plant Society. “But the old-boy network plants non-natives and is deaf to our arguments. Planting any trees anywhere sends chills down my spine. I do see progress, but then I hear some prominent person talking about planting a ‘trillion trees.’ ”

Sigg brightened when I asked about Angel Island. It had been blighted by eucalyptus desolation when I’d seen it. Now, he reported, virtually all the eucs have been cut and chipped, and native grasslands and scrub oaks have recovered. The California Department of Parks and Recreation had not been deaf to the society’s arguments. In the face of savage bullying from groups like POET (Preserve Our Eucalyptus Trees), it stood tall.

I think the great landscape photographer Ansel Adams put it best when he helped run tree-planting Boy Scouts off the prairie in what’s now the Golden Gate National Recreation Area: “I cannot think of a more tasteless undertaking than to plant trees in a naturally treeless area, and to impose an interpretation of natural beauty on a great landscape that is charged with beauty and wonder, and the excellence of eternity.” Treeless landscapes are not only natural, in many cases—they’re better for the Earth, too.