The past two decades have been hard on the West’s conifer forests, which have seen wave after wave of bark beetle epidemics turning once green landscapes brown and gray.
The world’s most long-lived organism, the Great Basin bristlecone pine, has stood firm against the beetle onslaught, unleashed by climate change, while other needle-bearing trees — like the lodgepole pines in Utah’s Uinta Mountains and the Engelmann spruce on the Wasatch Plateau — take a beating. While pine trees around them were dying, bristlecones have, until recently, been largely unaffected.
But in a sign of the worsening climate crisis, the tide now appears to be turning to the beetles’ favor and against these resilient trees, as scientists have now documented beetle-killed bristlecones, according to new research by the U.S. Forest Service’s Rocky Mountain Research Station.
In recent years, dendrochronologist Stan Kitchen began noticing beetles attacking bristlecones in Utah’s Wah Wah Mountains where he has been studying various pine species since the early 1990s. Some of Utah’s oldest trees are found on the northern end of the range that straddles the Beaver-Millard county line, including the world’s oldest ponderosa pine.
“I saw a few trees, including this 1500-year-old [bristlecone] tree that had succumbed. I’m no beetle expert, but it looked to me like possibly mountain pine beetle had infected it,” Kitchen said. “There were other trees that were hosting the mountain pine beetle and a few of the bristlecone pines have been sufficiently cross infected and succumbed.”
Around this time in 2017, he discovered another beetle victim. The ponderosa that he had previously identified as the world’s oldest was dead at 941 years of age.
He notified Barbara Bentz, a colleague and leading beetle expert, who mustered a research crew to gather data and bug samples in the Wah Wahs. The result was a scientific study published in April documenting the first known bristlecone mortality from bark beetles.
The tree deaths were limited to places where bristlecones grow near trees from other species, such as limber, ponderosa and pinyon pines, that were infected and killed by beetles. These trees were likely a stepping stone the insects used to launch attacks on the bristlecones, said Bentz, an entomologist who works with the research station’s Logan lab and lead author on the new study.
She believes the bug that killed these trees was the pinyon ips that had ravaged nearby pinyon pines and spread to the bristlecones, as opposed to the mountain pine beetle that has been doing much of the damage to Western forests and are also active in the Wah Wahs.
The beetles burrow into the pines’ bark and lay eggs in living tissues, which the larvae eat through, creating galleries in the trees’ phloem and cambium, eventually disrupting the transport of water and nutrients from the roots to branches.
“The larvae feed around the circumference of the tree,” Bentz said. “It’s like you took a hatchet and just went all the way around the tree.”
Kitchen, who retired last year, is not an author of the study, which does acknowledge his role in discovering the impacted bristlecones in the Wah Wahs.
Bentz’s and her colleagues documented far worse bristlecone mortality on Telescope Peak in California’s Death Valley National Park, first observed by Forest Service researcher Constance Millar in 2018. Like Kitchen, Millar had notified Bentz, one of the Forest Service’s go-to entomologists when beetles make a new appearance in a pine forest. What she saw on Telescope shocked her.
“I was totally surprised because of all the work that we’ve done, showing that they [bristlecones] usually don’t get attacked, and if they get attacked our research suggested that the beetles wouldn’t survive,” Bentz said.
Six years ago, Bentz had published research that concluded bristlecones appeared to be immune to the beetle assaults that were laying waste to so many other conifer species.
Last summer she returned to one of her previous research locations, high on Mt. Moriah in Nevada’s Snake Range, and was relieved to see bristlecones remained healthy despite clear evidence of a beetle invasion.
“There’s a lot of limber pine dying, but there’s not a single bristlecone attacked,” Bentz said.
And where bristlecone are dying, it appears that most of the invading beetles and their offspring do not survive long enough to leave the doomed tree to attack another one, according to the new study.
These findings are still a cause of concern: If the die-hard bristlecone is at risk from climate change, what does that portend for the West’s other conifers in the face of climatic conditions that experts predict will get hotter and drier as greenhouse gases continue building up in the atmosphere?
The Great Basin bristlecone, one of three of the five-needle pine species inhabiting the West, is perhaps the most resilient plant on Earth. It occupies rocky, high-elevation terrain between eastern California and western Utah, able to thrive in places where not much other woody vegetation grows.
It also thrives in environmental conditions that beetles don’t care for. But as the climate changes, those conditions are becoming easier on hungry bugs and harder on trees.
“All pine trees have [evolved] defenses against bark beetles. They produce sap when bark beetles bore through the bark into the living layer, the cambium underneath the bark,” Kitchen said.
The sap repels the beetles and seals the boreholes, but West’s warmer and drier climate has disrupted pines’ defense mechanism and enabled beetles to proliferate over winter.
“It can be overwhelmed when there’s too many bark beetles and when a tree becomes stressed from drought, it can’t produce as much sap because it doesn’t have water resources to do so and it’s much more vulnerable to bark beetles,” Kitchen said. “The drought may not kill the tree, but it sets it up to be killed by the bark beetle.”
The bristlecone whisperer
Otto De Groff, a Brigham Young University graduate student, is on a mission to visit all 380 known bristlecone stands. Over the past year, he has discovered three other locations in Utah where bristlecones are under attack and dying.
After seeing the bristlecone study, De Groff contacted Bentz to tell her about a dead bristlecone he observed last year in the Mountain Home Range, immediately west of the Wah Wahs. He led the beetle expert to the spot, where Bentz, wielding a hatchet that usually accompanies her into the field, pried away the bark of an afflicted tree and saw the tell-tale damage left by bark beetles.
This year during his travels, De Groff also discovered dying bristlecones in Johns Valley and in the Deep Creek Mountains in July.
“There is extensive bristlecone mortality in Johns Valley,” he said. “It’s these low-elevation stands. They’re the most stressed by drought. [Bristlecones] up higher at 10,000 feet, they still have been getting enough snow in the winter to defend against things like beetle attacks.”
These afflicted stands, like the ones in Bentz’s study, are intermixed with pinyon pine. Bentz intends to further investigate these sites.
“You can’t say what’s happening if you only look at one place,” she said. “We need to go to a whole bunch of places where this is happening and compare them to places where it’s not happening and doing some climate analysis.”
She wants to learn why bristlecones are dying in some places, but not in others.
“A lot of the mortality that we’re seeing is at these lower elevations in the southern margins of the range,” Bentz said. “It’s concerning because these genetic pools in these populations have evolved to live in these really harsh climates. All that genetic resource could be lost.”
Meanwhile, she and Millar will return to Death Valley next month to get a closer look and learn what can be done to save the park’s only population of bristlecones growing on Telescope Peak, the park’s highest point at 11,043 feet.
The summit is reached by a steep 7-mile trail passing through the dying forest, where the bristlecones stand side by side with limber pines, another long-lived five-needle pine that looks almost identical to bristlecones from a distance.
“The slopes are just incredibly steep with just tons of scree and stuff. So it’s very, very difficult to say, ‘I want to go see that tree and what killed it and what species it is.’ And you just can’t do it,” Bentz said. “All of our samples were from trees that were pretty close to the trail that we could access. So we don’t know of all the trees that are dead, what percentage of them are bristlecone and what percentage of them are limber.”
The team hopes to learn what percentage of the peak’s bristlecones are infected and advise the park on measures to safeguard the survivors.
Of greater concern is the fate of the Schulman Grove in California’s White Mountains, home to the oldest living thing. At 4,853 years old, the Methusaleh tree — named for the biblical patriarch who allegedly lived a mere 900 years—was already ancient when the Egyptians began building pyramids.
So far this grove appears to be safe, but one particularly aggressive measure the paper suggested calls for the removal of other pines to reduce the ancient bristlecones’ potential exposure to bark beetles. But it’s worth noting, Bentz cautioned, that these other pines themselves are extremely old and worthy of protection.
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