4 solutions for trees and forests threatened by a hotter world

Climate change poses a profound new threat to forests around the world, as Craig Welch explains in detail elsewhere in this special issue of National Geographic. Deforestation is an older and even larger threat. There is nothing more important that humans can do for forests, which have been on this planet for hundreds of millions of years, than cut our greenhouse gas emissions and stop cutting down old-growth trees.

But climate change won’t be stopped for decades at best, and trees and forests are already confronting it. Scientists are working on solutions to help them adapt. Here we look at four of them.

1. Help forests migrate to beat the heat

By Alejandra Borunda

Golden needles dust the ground and collect in Greg O’Neill’s hair like bright blond highlights as he pushes his way through a grove of tall, elegant larch trees in British Columbia’s Okanagan Valley. 

“Such a beautiful tree,” he says. “A proud species. When it finds its happy place, it goes wild.”

But the “happy place” for many trees, here and elsewhere, is changing as Earth’s climate warms. These thriving larches, in fact, didn’t sprout from tree parents in this valley, or even this country. They came from 284 miles south, in Idaho, where their ancestors adapted to conditions now common here: warmer summers, slightly shorter winters, different rainfall patterns.

They are part of an experiment designed to answer an increasingly urgent question: How can we help forests keep up with human-caused climate change? In plots like this, from Northern California to the Yukon border, O’Neill, a forester for the British Columbian government, and his colleagues have planted seedlings from larch and other species collected from groves along the West Coast to test the concept of assisted migration. They want to see how far and how quickly foresters need to move tree populations north to keep pace with climate change.

The problem is simple, says Cuauhtémoc Sáenz-Romero, a researcher at the Universidad Michoacana de San Nicolás de Hidalgo, in Mexico. “Climate is moving … and trees cannot walk.”

Since the late 19th century, when humans started burning fossil fuels and pumping huge quantities of carbon dioxide into the atmosphere, average global temperatures have risen about 1.1 degrees Celsius (2.4 degrees Fahrenheit). On the current emissions trajectory, they’re likely to rise at least that much more in the coming decades. 

On average worldwide, forests can expand their range up to 3,000 feet or so a year, as treelets often track their preferred climates toward the poles, or uphill. To keep up with the pace of today’s change, they’d need to be going six to 10 times as fast. In British Columbia the disparity is even greater: A 2006 study suggested the province’s climate zones would move northward about six miles a year.

For a place like British Columbia, where forests cover some 60 percent of the province and form the backbone of its economy and cultural identity, a forest mismatched to climate represents an existential threat. A maladapted tree—one whose genetics match a different climate reality—is more susceptible to weather disasters, diseases, and pests. (An illustrated guide to how heat and drought are killing trees)

The early 2000s brought that home. A series of drought years weakened many trees. Mild winters allowed the destructive mountain pine beetle, formerly kept at bay by the province’s bitter cold season, to move northward. Every year, from 1999 to 2015, tens of millions of trees were killed. In 2003, record-setting wildfires ripped through more than 650,000 acres of beetle- and drought-desiccated forest in British Columbia.

In 2009, the forestry service in British Columbia began the world’s biggest assisted migration experiment. At 48 sites, O’Neill and his colleagues planted neat grids of seedlings of 15 different species collected from 47 groves between Oregon and Prince George, British Columbia—152,376 trees in all.

About 10 years in, many of the trees that are flourishing came from populations a few hundred miles south, a sign of how much climate already has changed. The early data were so compelling that in 2018, British Columbia’s forestry agency officially adopted a policy that requires foresters to use seeds from warmer climate zones for the 280 million trees they plant each year.

The experiment upended one of the most basic rules of modern forestry: Plant local. Little genetic tweaks, honed over generations, may help a larch from Idaho better handle drier summers than one in British Columbia or may result in a British Columbian lodgepole pine growing later into the season than its Yukon cousin, says Sally Aitken, a tree geneticist at the University of British Columbia (UBC). But those local adaptations are needed in new places now.

Inside and outside of British Columbia, scientists argued bitterly over the ethics of moving species away from their current ranges. After all, past introductions had sometimes caused horrific invasive species issues. Others countered that humans already had foisted unprecedented change on ecosystems and that the risks of inaction could be greater.

Even with a lot of help in British Columbia, there’ll be hard limits to how quickly forests can adapt. Since no one suggests cutting down healthy forest to replant, foresters can make headway only by planting on burned or logged lands. At the current rate, the province won’t fully replace its logged forests for 80 years. Even then, new trees will just keep pace with climate change rather than outrun it, because it’s nearly impossible to plant trees far enough ahead of their current range for them to thrive many decades from now: Winter chills can stunt or kill seedlings of trees suited for warmer weather if they’re planted too far beyond where they currently thrive.

In a drizzly research garden on the UBC Vancouver campus, Ph.D. candidate Beth Roskilly peeks through a thicket of baby larches from all over western North America, planted tightly together in a raised bed. She’s searching for populations that are both heat and drought tolerant and cold hardy. “If we’re going to move larches up, we need to know they’re going to survive,” she says.

Meanwhile, climate pressures increase. In June 2021, driving near the Canada-U.S. border during a record-shattering heat wave, Aitken watched with horror as her dashboard thermometer ticked upward past 115°F. Outside the car, Douglas firs leaked a sticky resin and a sick, turpentine odor. “I’ve never seen trees that stressed out,” she says. The next day, enormous fires tore through the region; that autumn, unprecedented extreme rainfall caused weeks of landslides.

Despite such climate threats, Aitken is utterly clear: “It’s not like they’re a lost cause,” she says. “We’re just trying to figure out a way to keep up.”

2. Plant trees—but the right ones in the right places

By Craig Welch

Amid rolling farms and green pasture 150 miles northwest of São Paulo, Brazil, two tropical forests bloom as one. The first consists of a single species, row after row of non-native eucalyptus, planted in perfect lines like carrots. The other is haphazard, an assortment of dozens of varieties of native saplings.

There’s no denying it: This forest looks ridiculous. The gangly eucalyptuses shoot like witch fingers high above patches of stubby fig and evergreen trees. Yet these jumbled 2.5-acre stands of native trees, ringed by fast-growing exotics, are among many promising efforts to resurrect the planet’s forests.

The eucalyptuses, says Pedro Brancalion, the University of São Paulo agronomist who designed this experiment, get big so quickly they can be cut after five years and sold to make paper or fence posts. That covers nearly half or more of the cost of planting the slow-growing native trees, which then naturally reseed ground bared by the harvest. And this process doesn’t hamper natural regeneration.

You needn’t look far these days to find organizations trying to save the world by growing trees. There’s the Bonn Challenge, sponsored by the German government and the International Union for Conservation of Nature, which enlists countries to reforest 865 million acres by 2030, while Pakistan has its Ten Billion Tree Tsunami Programme. Major tree-growing campaigns, including Trillion Trees, sponsored by a trio of wildlife protection groups, and the World Economic Forum’s trillion-tree initiative, plant seedlings while also working to restore or conserve existing forests. Some companies even offer “buy one, plant one” deals for items from whiskey decanters to surfing gear.

Yet too many planting campaigns, forest experts say, still get too much wrong. On a tour of another of his rangy forest sites last fall, the Brazilian restoration ecologist drew newspaper-size boxes in the dirt to represent his plots. He found that if he leaves portions of each plot entirely free of trees—if he puts seedlings on only about half the land—the woodland fills in on its own. Decades on, he will have saved money and produced a thick wild forest while planting less.

Too often, tree-planting groups are so focused on getting credit for each seedling planted that they ignore what matters most: What kind of woodland is created? At what cost? And most important: How long will it last? Using numbers of trees as a magic “proxy for everything,” Brancalion says, you “spend more money and get lower levels of benefits.”

You can literally miss the forest for the trees.

Tree planting seems like a simple, natural way to counter the overwhelming crises of climate change and biodiversity loss. Trees provide wildlife habitat and slurp carbon dioxide from the atmosphere.

No wonder trees are hailed as the ideal weapon. Why not plant more and solve more problems? Yet for every high-profile planting operation, devastating failures have occurred. In Turkey, Sri Lanka, and Mexico, mass plantings have resulted in millions of dead seedlings or have driven farmers to clear more intact forest elsewhere. Trees planted in the wrong places have reduced water yield for farmers, destroyed highly diverse carbon-sucking grassland soils, or let invasive vegetation spread.

“I don’t think tree planting is a simple solution,” says Karen Holl, a restoration ecologist at the University of California, Santa Cruz, who collaborates with Brancalion. Reforesting the planet can’t substitute for cutting coal, oil, and natural gas emissions. Tree planting also can’t replace old-growth forests. It took hundreds or thousands of years to hone those intricate biological (and carbon-sequestration) systems. Saving them is even more important than growing new forests.

A tree’s true value is that it’s long-lived, which means someone must make sure it doesn’t die. Ethiopia, to great fanfare in 2019, claimed to have planted 350 million trees in one day, but Holl and her students have found little data to show how well those trees have fared. When Holl reviewed tree-planting proposals for the World Economic Forum, she found that even the best efforts monitored results for only 24 months. If the goal is carbon storage and biodiversity, “we can’t judge that in two years,” she said. Rather than simply planting a trillion trees, it’d be better to grow half as many but then make sure they’re “alive in 20 years.” 

Where—and how—they get planted matters too. Adding trees in the snowy far north darkens the landscape, letting it absorb more sunlight, potentially increasing climate warming. Planting them in native grasslands can damage equally important landscapes. In 2019, nearly half of the nations in the Bonn Challenge planned to sow tree plantations and log them regularly for timber or pulp rather than grow wild forests. That, despite the fact that natural forests on average sequester far more CO2.

So, what should we do?

To Brancalion, the answer is obvious: Restore native forests, mostly in the tropics, where trees grow fast and land is cheap. That may require planting. But it also may call for clearing invasive grasses, rejuvenating soils, or improving crop yields for farmers so that less land is needed for agriculture and more can be allowed to revert to forests. 

Brancalion has focused on Brazil’s Atlantic Forest, 75 percent of which has been removed for cities, cattle ranching, paper production, or growing sugarcane and soybeans. But that land often isn’t used well. Expanses of sugarcane land don’t produce a profit—they “cost money,” Brancalion says. Those areas—on steep slopes, near remnant forest patches—offer opportunities for restoration. Improving agricultural efficiency may make more land available. 

Combining eucalyptus harvests with native planting is just one reminder that successful restoration must provide value for local communities. Since farmers in Niger learned they grew more cereal grains by planting around—rather than clearing—woodlands, 200 million trees have come back. Not far from where I met Brancalion, residents aided by a local environmental nonprofit planted strips of trees for firewood and fruit and grew beans around degraded forests, helping black lion tamarin monkeys avoid extinction.

With resources limited and no time to spare, Brancalion says, jump-starting natural processes can help. In many cases, if we let nature do the heavy lifting, he says, “the forest can regrow quite effectively.” 

3. Build tougher trees with genetic engineering

By Sarah Gibbens

By the time 77-year-old Rex Mann was old enough to work in the forests of Appalachia, they were full of the dead.

“We called them gray ghosts,” the retired forester says of the American chestnut trees scattered throughout his former North Carolina home and still towering over the forest floors.

They were skeletal remains of majestic trees that once grew to be as much as 100 feet tall and 10 feet wide. Over the course of the 20th century, an estimated four billion of them, one-fourth of the hardwood trees growing in Appalachia, were killed by an Asian fungus accidentally imported in the late 19th century. It’s considered one of the worst environmental disasters to strike North America—and also a preview.

Emerald ash borer, sudden oak death, Dutch elm disease, oak wilt disease, walnut canker, hemlock woolly adelgid—in a globalizing world, many trees are facing pandemics of their own. And now climate change, with its catastrophic droughts, floods, and heat waves, is making it especially difficult to fight off attackers. Even Joshua trees, icons of the southwestern desert, are finding that the world is too warm.

All this has led some scientists to ask: Can we build better trees, ones that are more able to cope? And here again the American chestnut may soon set a precedent—this time on the path to resurrection. By tweaking its DNA, scientists say, they’ve created a blight-resistant tree that’s ready for a second act. If it works for the American chestnut, perhaps it can work for other similarly afflicted trees. 

“Some people say, ‘You’re playing God,’ ” says Allen Nichols, president of the New York chapter of the American Chestnut Foundation. “What I say is: We’ve been playing the devil for ages, so we need to start playing God, or we’re going to start losing a whole mess of stuff.”

The chestnut blight is caused by an insidious fungus that leaves orange-tinted cankers on a tree’s trunk and limbs. These splotchy indentations, reminiscent of a bruise, can choke off the tree’s flow of water and nutrients. The fungus, Cryphonectria parasitica, spares the young. But as tree bark ages, it cracks, letting microscopic fungal spores enter the trunk, where they release oxalic acid that kills tree tissue. 

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As a species, American chestnuts have survived by shooting up clones from the roots of dead trees. But it’s a Sisyphean task; blight is inevitable with age, and a tree’s ability to clone itself is not infinite.

In their attempts to save the chestnuts, foresters have sprayed the trees with fungicides, infected them with fungus-killing viruses, and even burned infected trees to the ground. Efforts to breed American chestnuts with Chinese counterparts to create a hybrid resistant to the blight began as early as the 1930s and in earnest in the 1950s. The American Chestnut Foundation began formal work on the hybrid in the 1980s. 

“Fast-forward 30-plus years of breeding work, and what we see is, blight resistance is much more complicated than we really thought,” says Tom Saielli, a forest scientist for the foundation.

Scientists now believe that as many as nine gene regions working together may be responsible for providing blight resistance, which makes breeding a challenge. The real question is, What is the right combination of genes to produce blight resistance? Breeding also requires many new generations to make progress, and each generation takes years.

Genetic engineering offers a controversial shortcut to creating a truly American blight-resistant chestnut. In the 1990s Charles Maynard and Bill Powell at the SUNY College of Environmental Science and Forestry in Syracuse, New York, began that quest, using what was then emerging technology. Powell says it was like having to “build a boat before we went fishing. We just started testing genes.”

His eureka moment came when he learned of a wheat gene that enhanced pathogen resistance in tomatoes. The gene produces oxalate oxidase—OxO for short—an enzyme that breaks down the acid produced by the blight fungus, rendering it harmless. By 2014 Maynard and Powell had successfully added this wheat gene to the chestnut’s genome. They christened the modified tree Darling 58, after Herb Darling, an engineer and avid supporter of their work. Trees grown in test plots at Syracuse proved tolerant of the blight.

Chestnut fans wanted to know when they could get Darling 58. Eight years later, they’re still waiting.

Powell is confident Darling 58 is safe, but transgenic trees inspire a fear of the unknown.

Who can grow genetically modified crops and where they can be grown are tightly regulated in the United States. Powell and his colleagues have asked the Department of Agriculture, the Food and Drug Administration, and the Environmental Protection Agency to deregulate Darling 58, affording it the status of a nonmodified tree. It’s the first time these agencies have grappled with such a request—to release a genetically modified tree into the wild—and it would set a precedent for other plant species.

“Once these are out in the forest, there’s no calling them back. There’s no way to reverse it,” says Anne Petermann, executive director of the Global Justice Ecology Project. Some Indigenous activists also are concerned the trees will violate their right to keep genetically modified organisms, or GMOs, off their land.

Despite these fears, scientists say genetic engineering is a powerful tool for keeping forest ecosystems intact. At Purdue University, researchers have been studying ways to genetically modify ash trees to fend off the emerald ash borer, a highly destructive beetle. In Canada, scientists have developed a genetically modified poplar that wards off spruce budworm. And at Powell’s lab in Syracuse, scientists are investigating new genes to embed in elm and chinquapin trees.

For fans of the American chestnut, like Mann, whose parents told stories of the tree’s demise and whose grandchildren may see its return, restoring the chestnut would be proof that environmental wrongs can be righted. At his home in Kentucky, Mann engages in what he calls “chestnut evangelism.” He says he’ll preach the value of chestnuts “until I start drooling.”

“A lot of people don’t even know all this death and destruction has been unleashed in our forest,” he says. “I think we have no right to just stand by and let all this disappear.” 

4. Leave forests alone to heal themselves 

By Andrew Curry

As a child in the 1980s, Prince Constantin zu Salm-Salm cherished walks with his grandfather through the two cathedral-like forests the family owned near an ancestral castle in central Germany. The 432-acre spreads of Norway spruce and Douglas fir, planted decades before he was born, were an investment—one the young prince hoped to inherit someday.

That all changed on a February night in 1990, when a hurricane named Wiebke hit the area with winds over 120 miles an hour, battering the tree-covered hillsides around Wallhausen.

After the storm finally passed, the two walked through the forests. Hundreds of towering 40-year-old spruces lay toppled. “He was in tears,” the prince recalls. “The big question my grandfather had to answer was, What do we do now?”

Today Germans face a similar reckoning but on a much larger scale. Since 2018, central Europe has experienced four straight years of drought or unusually high temperatures. Devastating bark beetle infestations have wiped out tens of thousands of acres of German spruce stands. Meanwhile, forest fires have sent woodsmoke wafting into the center of Berlin. In forest-loving Germany, the situation has sparked a national debate over how to respond. One option is to plant trees, replacing what’s been lost with more of the same.

The wooded hills around Wallhausen represent another possibility. Prince Salm is part of a growing group of German forest owners who have turned to what’s known as close-to-nature forestry. This hands-off approach avoids tree planting when possible and advocates largely sticking to native species. The aim is to replicate the ecosystems of wild forests by leaving deadwood behind and selectively harvesting only the most mature trees.

Prince Salm’s family have cultivated wine in the area for more than 800 years. After the devastating impacts of Wiebke they came to an unusual decision. “We said, ‘Nature knows better what should be here,’ ” Prince Salm says.

Their forests are an hour west of Frankfurt, on north-facing slopes that can’t support vineyards. Aside from hunting deer and wild boars, and harvesting some of the biggest trees each year, they leave the forests largely alone.

On a late fall day not long ago, Prince Salm plunges through his forest in green rubber boots and a blue down vest. Beneath the crowns of tall Douglas firs that survived Wiebke, young oak, beech, and cherry trees that took root in the hurricane’s wake are aflame with the last of the season’s red and yellow leaves.

“Everything you see here came in naturally,” he says, as his brown-and-white cocker spaniel disappears into a dense tangle of saplings and brush. “The only investment we make is roads and hunting.”

In a way, German forestry is edging away from its roots. The nation was one of the first to approach forests as a resource to be managed. In 1713 an administrator named Hans Carl von Carlowitz advocated that landowners plant new trees to replace what they cut down for mining and metal production. It was the genesis of the concept of sustainability—but in a narrower sense than the word is used today. Following Carlowitz, German foresters have approached trees with industrial efficiency, planting fast-growing species such as spruce in neatly spaced rows. The approach caught on around the world and is still popular in Germany.

A century ago a botanist named Alfred Möller pushed back. He argued that forests were complex organisms and that trees shouldn’t be cultivated like slow-growing stalks of wheat. Instead, forests should be managed the way nature might: by selectively felling individual trees while maintaining a continuous cover.

Möller, who died in 1922, never had a chance to see his ideas put into practice. After World War II, forests all over Germany were logged to help rebuild war-damaged cities in Britain, France, and the U.S.S.R. To replace them, foresters planted millions of trees, mostly spruces, in the 1950s. It was the beginning of a booming forestry industry that included foresters like Prince Salm’s grandfather. Timber and its by-products are now a $150-billion-a-year enterprise employing more than 700,000 Germans. A third of the country is covered with trees today.

That’s why years of drought and infestation have come as such a shock. For the first time, Germans are confronting the possibility of a future with dramatically fewer trees. “We don’t want to imagine this in Germany, which thinks of itself as a forest country,” says Pierre Ibisch, an ecologist at Eberswalde University for Sustainable Development. “But we face this risk.”

The German government has declared the situation a national crisis, providing forest owners with nearly two billion dollars in subsidies to remove beetle-damaged deadfall and replant forests.

Some close-to-nature forestry advocates say that might be a mistake. Instead of rushing to plant more trees, they see an opportunity to do less. Leaving deadwood and tree canopies to slowly rot returns nutrients to the soil, boosting the health as well as the diversity of surviving trees. “From our perspective, less is always more,” says Knut Sturm, forest manager for the city of Lübeck.

There are caveats, of course. Close-to-nature forests can be profitable, but they require the timber industry and foresters to adjust to a different way of doing business. Sawmills, for example, are set up to process narrow, straight spruce trunks, not portly old-growth oaks.

As climate change accelerates, it’s also important to consider planting more drought-resistant species imported from elsewhere, says Marcus Lindner, a scientist at the European Forest Institute. “It’s possible to shift to more close-to-nature silviculture but still bring in more drought-tolerant species.”

Back in Wallhausen, the sun is dropping low, and lights are beginning to come on in the village below. “I want for my children that they can choose from 10 different species, not just Douglas fir or spruce,” Prince Salm says, calling his panting spaniel to heel and turning for home. “We have to make sure the same mistakes aren’t made all over again.”