The world’s longest-lived trees couldn’t survive climate change

The Washington Post/Sarah Kaplan

16:30 JST, July 15, 2022

The trees had stood for more than 1,000 years. Their sturdy roots clung to the crumbling mountainside. Their gnarled limbs reached toward the desert sky. The rings of their trunks told the story of everything they’d witnessed – every attack they’d rebuffed, every crisis they’d endured. Weather patterns shifted; empires rose and fell; other species emerged, mated, migrated, died. But here, in one of the harshest environments on the planet, the bristlecone pines survived. It seemed they always would.

Until the day in 2018 when Constance Millar ascended the trail to Telescope Peak – the highest point in Death Valley National Park – and discovered hundreds of dead and dying bristlecones extending as far as she could see.

The trees’ needles glowed a flaming orange; their bark was a ghostly gray. Millar estimated that the damage encompassed 60% to 70% of the bristlecones on Telescope Peak.

“It’s like coming across a murder scene,” said Millar, an emerita research ecologist with the U.S. Forest Service who has studied bristlecone pines for the better part of 40 years.

In a study published this spring, she and fellow researchers showed that the West’s worst drought in at least 1,200 years had critically weakened the trees. Voracious bark beetles – a threat to which bristlecones were previously thought immune – delivered the death blow.

After outlasting millennia of disruptions and disaster, human-caused climate change is proving too much for the ancient trees to bear. Rising temperatures have caused an explosion in the populations of insects that threaten the trees and undermined their capacity to defend themselves, scientists say. Although Great Basin bristlecone pines are not considered at risk of extinction, cherished specimens and distinctive populations are struggling to survive.

And bristlecones are not the only victims. At this very moment, a fast-moving fire is scorching through the iconic giant sequoia grove in Yosemite National Park. Cedars are choking on saltwater as rising seas engulf shorelines on the East Coast. A rare oak species clings to life as the Texas desert grows hotter and drier.

A new study, published Wednesday in the journal Nature, found that climate change has pushed almost a quarter of Earth’s best-protected forests to a “critical threshold” for lost resilience – the point at which even a minor drought or heat wave could tip them into catastrophic decline.

Standing amid the devastation atop Telescope Peak, Millar realized, “This could be a harbinger of what could be happening in the future.”

If nature’s consummate survivors could not cope with catastrophic warming, she wondered, what did that mean for the rest of life on this planet?

And if humanity didn’t heed the warnings of these fallen elders, what would it say about us?

– – –

No organism on Earth is known to live as long as the Great Basin bristlecone pine. The oldest documented tree, a well-hidden specimen nicknamed “Methuselah,” after the long-lived biblical patriarch, was a sapling when the ancient Egyptians built their pyramids more than 4,500 years ago. Even the relatively youthful trees in Death Valley are older than gunpowder, paper money and the English language.

“Their presence and their stability and their fortitude stretches our own sense of time,” Millar said. “It just slows people down … and reminds us of how things were before humans were here.”

The secret to their survival is their ability to withstand what others cannot. They exist at higher elevations than almost any other tree, thriving in the rocky, meager soils near rugged mountain peaks. Their branching root systems and waxy needles help them make the most of scant water. They produce a thick resin that traps insect invaders and quickly patches wounds. Their genomes, which are nine times as long as a human’s, contain a multitude of mutations that give them a better chance of adapting to changing conditions.

Few trees can take a beating like a bristlecone. They deal with crisis by sectioning off parts of their structures, enabling the rest of the tree to keep living while the injured limb is allowed to die. Their wood is so dense it rarely rots; the trunks of dead trees will remain standing for millennia.

The species needs all these strengths to exist in Death Valley – a forbidding environment even by bristlecone standards. The park is farther south than any other bristlecone habitat, and hotter and drier than any other place in the United States.

Scores of other creatures benefit from the trees’ persistence, Millar said. Bristlecones provide shade to elk and bighorn sheep, and shelter chipmunks and jack rabbits from predators and fierce weather. They allow snow to cling longer to the mountains’ upper slopes, ensuring a supply of meltwater during the brutal summer months.

And their staying power makes them invaluable to scientists. Bristlecone tree rings have allowed researchers to reconstruct a record of Earth’s climate going back thousands of years; the field of research is known as “dendrochronology.” The rings reveal when volcanic eruptions occurred, how long droughts lasted, even when the surface of the sun became blotted by magnetic storms.

“By translating the story told by tree rings, we have pushed back the horizons of history,” the pioneering dendrochronologist Andrew Ellicott Douglass wrote in National Geographic in 1929.

He compared tree ring records to the Rosetta Stone and called the ancient trees of the desert Southwest “prehistoric jewels.”

In preserving the planet’s past, bristlecones also have given humans a key to understanding our future. They capture the interactions between greenhouse gases, rising temperatures, shifting weather patterns and altered ecosystems, and they allow scientists to project what will happen as Earth continues to warm.

“It’s well spelled out that the loss of these trees would remove this natural archive,” Millar said. “I hope the general public will realize what a loss that would be.”

– – –

After her grisly discovery atop Telescope Peak, Millar immediately contacted Barbara Bentz, a research entomologist for the Forest Service based at the Rocky Mountain Research Station in Logan, Utah.

Just a few years earlier, Bentz had surveyed bristlecone populations across the West and found that few were succumbing to the bark beetle outbreaks that decimated so many other species. She felt confident that the trees would remain resilient even as rising temperatures caused beetle populations to explode.

Yet, when Bentz peeled a piece of bark off one of the Death Valley bristlecones, she found scores of tiny tunnels created by beetle larvae as the insects chewed through the tree’s living tissue.

“Oh, no,” Bentz thought to herself. “It really is beetles. Oh, no.”

She and her colleagues uncovered further evidence of insect damage in Utah’s Wah Wah Mountains, where young bristlecones were attacked by a small brown beetle called a pinyon ips.

In both cases, the beetles were unable to complete their life cycles inside bristlecone pines, Bentz said. Instead, it seemed that they were reproducing in nearby trees from of species different from the bristlecone. Higher temperatures – Inyo County, home to Death Valley, is already more than 1.6 degrees Celsius (2.9 degrees Fahrenheit) hotter than in the preindustrial era – allowed the beetles to reproduce faster and caused their populations to swell dramatically. When the surplus spilled over into bristlecones, their defenses were overwhelmed.

The scientists think the trees had been so stressed by drought that they could not fend off attacks they once would have vanquished with ease. Climate analyses showed that 2020 soil moisture levels in Death Valley and the Wah Wah range dipped to their lowest levels in at least 40 years.

Millar said the discovery should raise alarms all over the West, where lakes are shrinking, snowpacks are declining and heat records are being set. The White Mountains – home to Methuselah and many more of the world’s oldest bristlecones – lie just 100 miles from Death Valley and have a similar climate. They could easily become the next site of a beetle attack.

“We don’t want Methuselah to die on our watch,” Millar said.

Although the species is not considered at risk of extinction, she added, the death of important subpopulations is still a reason to mourn. Each disappearance represents not only a loss for the landscape, but also is a sacrifice of the genetic diversity those populations contained.

Millar recalled another visit to Death Valley, when she hiked through an area called the Last Chance Range in search of a bristlecone pine cluster that was rumored still to exist there. By the time she found a single remaining tree, it was dead.

If the specimen had a gene that made it uniquely capable of surviving in that forbidding landscape, there was no chance of resurrecting it. No hope of collecting seeds for replanting, or taking a cutting in an attempt to produce clones. No opportunity to draw on the tree’s DNA to help the rest of the species survive.

“That, to me, is the dramatic element of watching a population go extinct,” Millar said: All of that unique genetic material, the product of thousands, if not millions, of years of evolution, is gone for good.

Arid forests around the globe have experienced a devastating loss of resilience in the past two decades, according to the analysis published Wednesday in Nature. Satellite imagery shows that these ecosystems are less able to bounce back after a fluctuations in weather or periods of drought. Tropical and temperate forests – the steamy Amazon, the North Woods of Minnesota – are in similar decline.

The trend was seen in forests altered by human activities as well as those that remain almost untouched by direct human action – an indication that climate change, rather than local deforestation or pollution, is primarily at fault.

Indeed, 23% of untouched forests are approaching the point at which they could be pushed into an abrupt and irreversible transition, the scientists said. Rainforest could turn into grassland. Thick stands of pine might give way to shrubs and desert.

“It’s a strong warning, I think, for society,” said lead author Giovanni Forzieri, a professor of sustainable development and climate change at the University of Florence.

He pointed out that most of the world’s climate plans count on forests to pull planet-warming gases out of the atmosphere. If these ecosystems collapse, humanity will find it difficult, if not impossible, to stave off catastrophic warming.

– – –

To Murphy Westwood, the vice president for science and conservation at the Morton Arboretum in Illinois, each loss feels like a moral failing.

“It’s overwhelming and almost crushing,” she said, “the stark reality of the biodiversity crisis that’s on our hands.”

Last year, Westwood helped publish a sweeping assessment of 58,497 tree species worldwide that found that nearly 30 percent are at risk of being wiped out. At least 142 species have gone extinct in the wild.

It’s not just trees. With global temperatures already more than 1 degree Celsius (1.8 degrees Fahrenheit) higher than in the preindustrial era, the Earth is losing species at a rate hundreds to thousands of times faster than normal.

If the world remains on its current warming track, as much as 29 percent of all creatures on land will face very high risk of extinction. In the ocean, the destruction will be even greater.

But humanity’s growing understanding of all we might lose, Westwood said, also offers us a chance to change course. We can conserve rare organisms and protect fragile ecosystems. We can reverse deforestation and stop burning the fossil fuels that cause the planet to warm.

“If we can see it happening in front of our very eyes,” she said, “then we know we have the tools and knowledge to prevent another extinction.”

She pointed to an expedition she helped direct this spring, which rediscovered a tree that scientists had believed extinct.

Rising temperatures and dwindling water over the past century had killed off every known specimen of Quercus tardifolia, an oak known for its fuzzy evergreen leaves. But Westwood and other scientists held out hope that the species still clung to existence somewhere.

After weeks of trekking through the canyons of Big Bend National Park in Texas, they stumbled upon a single tardifolia tree – scorched by fire and ravaged by fungal disease but undeniably, miraculously, alive.

The researchers plan to collect acorns and cuttings from the tree that can be used to regrow the species in botanic gardens and arboretums.

“We have a second chance to prevent a species extinction,” said Wes Knapp, the chief botanist for the conservation nonprofit NatureServe and another member of the expedition. “That’s really rare, to have a second chance in nature. It means we can move. We can act. That’s what we have to do now.”

Farther west, Millar and Bentz plan to return to Death Valley this August to more thoroughly assess the state of the park’s bristlecone pines and then develop strategies for preserving the trees that remain. They are developing chemical repellents based on the trees’ natural defenses to protect “high value trees,” such as Methuselah. And they are surveying all the nation’s bristlecone stands, searching for the genetic variations that might help the species survive.

Amid the challenges facing both trees and humanity, Millar said, the bristlecones offer lessons in how to hang on. Their tenacity is an antidote to despair. Their genetic diversity is a bulwark as they face the unknown.

“From a human standpoint, I think that translates into innovation and resilience,” Millar said.

To live like a bristlecone is to never let go of hope.