Focus on Arts and Ecology

An early warning came in 2002, during the Southwest’s worst drought in five decades. Weeks before meeting Turner, I scrambled up a dusty embankment near New Mexico’s Bandelier National Monument. Beside me, Craig Allen and Nate McDowell, an earth scientist at the Pacific Northwest National Laboratory, examined a picture Allen had taken in 2002. It showed dense throngs of piñon pines, their needles tinged orange because they were dying.

Allen swept an arm toward a nearby mesa. He’d studied forests in this scratch of arid woodland near the Jemez Mountains since the 1980s. Now the adult pines from his picture were gone. What remained was cracked earth, hardy junipers, and an occasional seedling.

A drought in the 1950s had brought even less rain, and yet between 2002 and 2004 the impact on trees was worse: In some areas, more than 90 percent perished, many falling victim to bark beetles, natural predators that spread as never before. All told, some 350 million piñons, New Mexico’s state tree, died across the Southwest. Unprecedented fires eviscerated hundreds of thousands of acres of ponderosa pines.

Allen was taken aback by the severity. But bit by bit, he, McDowell, and their colleagues came to understand: This drought was hotter. The slight increase in temperature attributable to greenhouse gas emissions was already enough to set the death of New Mexico’s trees in motion.

And what’s become ever more clear to Allen, through his own work and that of many others, is that trees the world over are vulnerable to the added heat. The warmer atmosphere sucks more moisture from plants and soil. To cut their losses during droughts, trees close pores in their leaves, called stomata, or shed leaves entirely. But that limits the CO2 they take in, leaving them both hungry and parched all at once. When it’s especially hot, they even leak some of the water they’re desperate to retain.

When soil gets dry enough, trees can no longer maintain pressure in the internal conduits that carry water up to their leaves. Air bubbles interrupt the flow, causing fatal embolisms. Some trees protect themselves with deeper roots, for example, or by storing more water—but those investments come at the expense of growing taller to compete for light and space with other trees.

The upshot, scientists figured out in just the past decade, is that many trees in most landscapes, from the hot, rainy Amazon to cold, dry Alberta, are operating at the limits of their hydraulic systems, even under normal conditions, with little safety margin. That means a hot drought can push them over the threshold. The 2002 drought in the Southwest did exactly that: Tree-ring records would later show it was the driest and worst year for growth in a millennium. No other year even came close.

All this awakened Allen to what he now sees as a grave global threat. “Seeing the transformation of this landscape that I’d studied my whole adult life … climate change wasn’t theoretical anymore,” he told me. He started tracking the mass mortality events elsewhere. Over the next two decades, heat and drought would kill billions of trees directly and indirectly—in Spain, in South Korea, throughout Australia. In central Siberia, Russia lost two million acres of firs. In Texas in 2011, drought killed more than 300 million trees—one out of every 16 in the state.

Increasing warmth helped deadly forest pests spread, weakening trees and letting beetles and moths live through the winters or reproduce more often. Such invasions wiped out trees in Honduras, Turkey, and Algeria. In central Europe they arrived as a shocking new plague.

On a chilly day last fall, I struggled up 227 steps inside a former Cold War surveillance station on a 4,300-foot peak outside Prášily, a Czech village near the border with Germany. I huffed to keep pace with Petr Kahuda, a ranger at Šumava National Park, and Zdeněk Patočka, a forest scientist at Mendel University. The tower was built in the 1960s to listen in on NATO radio transmissions, but after the Iron Curtain fell, the Czech government opened it and this 170,000-acre park to the world. At the top, a circular balcony overlooks rolling forests that once fueled the region’s glass industry. Now, huge portions of its trees are dying, victims of bark beetle attacks.

In 2018 central Europe experienced its worst drought in five centuries. Summer temperatures hit nearly six degrees Fahrenheit above average. Tree deaths skyrocketed, and weakened survivors attracted beetles. Worst hit was Czechia. Loggers raced to salvage what they could. People were so desperate, Kahuda said, that one man offered Šumava National Park his sheep, hoping their smell might drive away the insects.

In Germany, 750,000 acres of forest died from 2018 to 2020. No one knew quite how to respond. History aggravated the crisis: Almost no native forests remain in central Europe. Humans have thoroughly transformed the landscape. Originally dominated by beech and oak, many forests had been replanted with Norway spruce and pine. After World War II, clear-cuts were made to ship timber and pay reparations to the Allies.

But while spruce grows naturally at higher, cooler elevations, foresters also planted it down low. It did fine there for 70 years. Then, says Henrik Hartmann, a forest expert at the Max Planck Institute for Biogeochemistry, “climate change made this formerly suitable habitat inadequate.”

For a while, Turner kept her faith in Yellowstone’s cycle of fire and rebirth. Trees die; it’s part of the equation. But at a 2008 conference in Jackson Hole, Wyoming, she was confronted with the possibility that the equation had changed. A colleague presented maps suggesting that Yellowstone in coming decades could see fire seasons like 1988’s nearly every summer. That year “would no longer be exceptional—and the exceptional years would be out of control,” Turner recalls.

She didn’t buy it at first. For thousands of years Yellowstone’s monster blazes had burned erratically at different intensities, scorching some spots and skipping others. The mosaic let animals and trees recolonize easily. Her own work, influenced by that long-ago chopper ride, had thoroughly documented that pattern. But what if the system no longer worked that way?

Turner started investigating. She learned that baby pines grew poorly in hot, dry seasons. She’d been taught that young lodgepoles were too green to burn, but she found them supporting explosive fires. She watched areas of the park burned in 1988 catch fire again. She saw fires crashing through before young trees produced mature seed cones. Some burned so big and hot that no seed trees survived to regrow the forest.

In five spots around Grand Teton and Yellowstone, Turner found forests coming back sparsely or not at all. Climate change was reshaping some of the most storied scenery. Simulating a future in which we don’t curtail emissions, she caught glimpses of some of her favorite places as her children might one day see them: At Oxbow Bend, where Mount Moran is reflected in the Snake River, the thick stand of conifers could be replaced by sagebrush, grasses, and aspens; along Firehole Canyon Drive or the Madison River, the pine forests could become meadows.

Turner had thought of Yellowstone as “the most resilient place in the world.” Now her research showed its forests transitioning to a new state. Other scientists were reaching similar conclusions elsewhere. Camille Stevens-Rumann, a forest ecologist at Colorado State University, examined 1,485 sites from 52 fires in Colorado, Idaho, Montana, and Washington. The number of burned sites that didn’t recover jumped from 19 percent before 2000 to 32 percent in the years after. “And by ‘not recovering,’ I mean not a single tree—not one,” she says.

Not long ago, the U.S. Forest Service mostly planted trees only after forests had been logged—it counted on burned areas regenerating naturally. Now, “over 80 percent of our reforestation needs are being driven by catastrophic wildfire,” says David Lytle, the agency’s forest and rangeland management director. More than half of the millions of acres burned recently in 154 national forests won’t grow back without replanting. Even then, on tens of thousands of acres, seeds may never take root, Lytle says.

But around the world, more than just drought and fire are at play. After extreme heat and drought had weakened mangroves across hundreds of miles of northern Australian coast, an El Niño event in 2015-16, likely worsened by climate change, caused a temporary regional drop in sea level. Eighteen thousand acres of mangroves died of thirst. In southeastern Brazil, the same El Niño drove down precipitation, stressing mangroves along the flat, brown Piraquê-Mirím River. Then, one June day in 2016, plum-size hail pummeled this hot landscape for the first time on record, as 60-mile-an-hour gusts blew foliage off trees and drove trunks sideways across 1,200 acres.

Five years later I visited with Angelo Bernardino, an oceanographer with Federal University of Espírito Santo. From a boat on the river, we watched soil around the dead trees sloughing into the water, ensuring that few if any mangroves would ever sprout here again.

HOW THESE ANCIENT TREES COULD WEATHER CLIMATE CHANGE

If any species could withstand climate shifts, you might think it’d be giant sequoias, many of which have stood since the reign of Julius Caesar. Instead, change has come frighteningly fast.

In 2012 the cover story in National Geographic’s December issue profiled one stunning specimen in Sequoia National Park. At 247 feet in height, nearly half that of the Washington Monument, the President, as the behemoth is called, was thought to have been a seedling when fewer people walked Earth than live in modern France. It held more leaves than there are people in China. Our story told of sequoias’ remarkable resilience: the way tannins supposedly made them impervious to wood-boring beetles; how their thick bark was nearly flame resistant. Researchers were wary about the future but not alarmed.

Last summer, less than a decade later, I sat in the canopy of a nearby sequoia and stared over at the President. My throat itched from the smoke of a nearby wildfire. My legs ached from hauling myself 200 feet up a climbing rope to join forest ecologist Anthony Ambrose. I’d come because he and other scientists were suddenly rattled.

In 2014, two summers after that story was published, sequoias began shedding needles, a severe move to curb water demand during a horrendous drought. Then scientists noticed 33 trees succumbing to fatal beetle attacks. Ambrose saw tunnels carved through bark. He saw branches trying to push insects out by oozing pitch. He worried other trees might be next.

Before then, sequoias were considered “freaks” of the conifer world because “nobody had ever seen one killed by insects,” Nate Stephenson had told me the day before I met Ambrose. Stephenson would know. After studying these monarchs for more than 40 years, he probably understands them better than anyone else.

In 2015, shortly after the needles fell and the bugs arrived, Stephenson met with Christy Brigham, who’d recently arrived as the park’s chief of resources. “How bad is it?” she asked. Stephenson saw no reason for panic.

Drought and fire threats to sequoias had been predicted by climate modelers, but most didn’t expect serious danger for decades. Sequoia and Kings Canyon National Parks had pioneered the setting of prescribed burns to clear brush and logs from the understory so that wildfires didn’t explode. The parks would now light even more controlled blazes, Brigham decided. She hired Ambrose and forest ecologist Wendy Baxter to track how sequoias were managing water stress.

Ambrose has climbed enough sequoias to know they are tough old beasts. He’s seen them struck by lightning only to grow new canopy branches. He’s watched them slow their photosynthetic machinery in dry times. Trees that can drink 800 gallons of water a day don’t survive thousands of years without learning to “hunker down,” he says. But by 2021, as we sat together staring at the President after the most shocking fire season on record, Ambrose was wondering how much more these trees could take.

Sequoias need low-intensity ground fires to release seeds from their cones and clear soil, so seeds can take root. Their high branches make them unlikely hosts for canopy fires. But in 2020 our history of suppressing fire collided with a rapidly changing climate. The same dry spell that cost sequoias foliage had killed tens of millions of trees—sugar pines, incense cedars, and white firs—in densely packed forests nearby. That’s where the Castle fire began.

Soon it jumped ridges and spotted into the sequoias. Long flames ignited their crowns. Heat and wind shot smoke tens of thousands of feet high. Embers exploded. High branches collapsed, plunging seed cones into flames, incinerating future generations.

In one grove Brigham found hardly any seeds. “There was nothing on the ground except ash. We have never seen that before. Never.” After the fire, Brigham took stock. Up to 14 percent of all the large sequoias in the Sierra Nevada, their native habitat, were dead or mortally wounded.

Months after I left Ambrose, it happened again. Fires in September 2021 charred sequoia bark and sent twigs raining for miles. Ambrose’s study trees lost water 24 hours a day. Flames came so close to the General Sherman—the biggest tree on Earth—that firefighters wrapped it in flame-resistant material.

The 2021 fires claimed another 3 to 5 percent of large sequoias. Up to 19 percent of these magnificent trees—trees that had weathered everything for a millennium or more—had been lost in just two years.

Losing forests to climate change isn’t just about such heartbreak. There are other consequences for people and wildlife. Wildfire smoke increasingly fouls the air of major cities such as San Francisco and Seattle. Australia’s 2020 megafires killed 33 people—and a billion animals, including 60,000 koalas. The fires may have expanded the country’s list of endangered animal species by 14 percent.

Losing forests also releases carbon that amplifies the climate threat. The future on that score looks uncertain but worrisome.

In North America’s boreal forest, from Alaska to Newfoundland, massive fires now release incredible amounts of carbon—not only from the trees themselves but also from the moist peat soils in which they grow. Jennifer Baltzer, a forest ecologist at Wilfrid Laurier University in Ontario, has found that in many burnt patches, the dominant species, black spruce, is being replaced by other species such as aspen—which in principle might soak up more carbon than spruce over time and be less likely to burn. But soils hold most of the carbon in the boreal region, and for now they seem very vulnerable.

Meanwhile, in the boreal forests of Siberia, intensifying fires have mutated recently into multimillion-acre monsters that threaten to release huge reserves of ancient carbon from the permafrost. Those burns are turning some forests into shrublands or grasslands, which store less carbon, says Heather Alexander of Auburn University in Alabama. Yet the switch to a lighter-colored landscape also has a cooling effect, because it reflects more sunlight than darker forest—especially when blanketed by winter snow. The bottom line for climate, Alexander says: “Unknown.”

The Amazon rainforest presents a clearer and more urgent picture. It produces much of its own rain, recycling water vapor over and over. The clearing of forest for cattle ranches and soy farms has accelerated again under President Jair Bolsonaro, and climate change may be hastening the approach of a dangerous tipping point. Grueling droughts in 2005, 2010, and 2015-16 killed billions of trees outright and helped spread fires that killed more. As forest is logged, burned, or dried out, that reduces rainfall in a self-reinforcing spiral. Some scientists fear that spiral threatens to send the world’s biggest rainforest hurtling toward a transition to a savanna.

Each region of the world faces its own particular challenges, but the threat to forests is general and global. “There’s just red flag after red flag where these forested ecosystems are being pushed right to their limit,” Baltzer says.

Yet increasingly, governments from Japan to the United Kingdom are setting up complex trading schemes that allow businesses to offset fossil fuel emissions by protecting forests rather than to cut emissions at the smokestack. Often those schemes don’t account adequately for the possibility that forests may not be protectable. As I was visiting sequoias last year, a wildfire in Oregon was releasing carbon that tech giant Microsoft had purchased to offset its own emissions.

No one knows what awaits this summer, or next. But it’s time we embraced our new reality. We can no longer forestall rapid changes to some forests. The planet won’t stop warming until we completely halt fossil fuel emissions, and that will take decades. As Craig Allen witnessed in New Mexico and Nate Stephenson has seen with giant sequoias, some changes may be drastic.

But we can keep things from getting even worse. To start, we must halt the destruction of native forests, especially tropical, boreal, and temperate old-growth forests. The benefits they provide aren’t replaceable. The good news: Many are still healthy, for now.

For example, humans have cleared far less of the Congo rainforest, the world’s second largest, than of tropical forests in Asia or South America. The forest is getting less precipitation, but it’s showing resilience. While some trees in Gabon produce less fruit, providing less food for forest elephants, the Congo has avoided widespread tree mortality. Even in Brazil and Southeast Asia, millions of square miles of lush forest remain intact.

“We need to protect the forests we have,” says Robin Chazdon, a restoration expert with the University of Connecticut. “That’s number one.”

We also need to manage forests better, especially for fire. In cooler, dry months in northern Australia’s Arnhem Land, Indigenous rangers carry drip torches or drop fire starters from helicopters to ignite ground-crawling blazes in the tall grass. So far, that has dramatically curbed explosive late-summer forest fires. In the U.S., the White House announced plans in January to help government and private landowners start more prescribed burns and thin more forests, where appropriate, with logging. The aim is to reduce fire risks on four times more land, up to 50 million acres, over 10 years—if Congress provides the money.

But that’s not enough. We also need to restore damaged forests, primarily in equatorial regions, where native trees can come back quickly, but elsewhere too. The infrastructure bill signed by President Joe Biden last fall authorizes billions of dollars to increase nursery and seed-growing capacity and kick-start the largest U.S. reforestation campaign in history by replanting four million acres in a decade.

And of course we need to break our fossil fuel addiction, quickly.

On my last day in Yellowstone with Turner, we visited old burns from another 2016 fire. This one had ripped across a plateau above the Madison River, which also had burned in 1988. The recent blaze had so scorched the landscape that it even incinerated downed trunks, leaving nothing but lines of white ash that stretched like shadows across blackened soil. Turner called them “ghost logs.” In 30 years of traipsing through fire scars, she’d never seen ground so pummeled by fire.

Do we want even more of this?

This spring marks 150 years since President Ulysses S. Grant signed the act creating Yellowstone, America’s first national park. It required “preservation, from injury or spoliation” and “retention in their natural condition” of the park’s wonders. The effort that entails has expanded since Grant’s day, when threats were direct and local. Turner projects that if global temperatures were to rise four degrees Celsius (7.2 degrees F) from preindustrial values, the region’s high-elevation spruces and subalpine firs, such as those near the Snake River’s headwaters, could be wiped out. Forest cover could drop by half by 2100. The density of what remains would drop even more.

That’s far from inevitable. If the world’s nations keep their current promises, the planet will warm less than three degrees Celsius (5.4 degrees F). Stabilizing emissions closer to two degrees or less could limit forest losses in Yellowstone to 15 percent. High-elevation trees would still struggle, and there’d be more Douglas firs and aspens. But some old growth would persist. Yellowstone’s forests, like many in the world, will never be the same. But they might be close.

Senior writer Craig Welch has been reporting on climate change for more than 20 years. In the past year he has written cover stories on electric cars and the culture of whales.

This story appears in the May 2022 issue of National Geographic magazine.

(Sources: National Geographic)