The Ancient Bristlecone Tree Faces Two Major Threats: Bark Beetles And Us

If you’ve ever traveled to Death Valley National Park, the bristlecone pine woodlands are a sight to see.

The oldest-known tree species in the world grows to 15 to 30 feet, but the contorted trees with their tightly packed pine needles are facing major threats: bark beetles and us.

Bark beetles are the size of a grain of rice and though they look anything but menacing, hordes of them can become an aggressive tree killer.

And our changing climate conditions are accelerating the rate at which bark beetles feast on the bristlecones, specifically in the Great Basin (that’s areas in the mountain ranges in eastern California, Nevada and Utah), according to recent research from scientists part of the USDA Forest Service.

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“The bristlecones are normally extremely resilient, but the drought and climate change have stressed the trees to the point where they are not resilient to the bark beetles, and the bark beetles are killing them,” said Abigail Wines, a Death Valley national park ranger and park management analyst.

Wines said about 70% of the bristlecone pines in Death Valley have been wiped out so far.

How bristlecones battle bark beetles

Bristlecones like to grow in habitats at the border of environmental extremes, like the ones in Death Valley National Park, where the highest peaks are covered in frost during the winter. The park is also the hottest place on Earth and the driest place in North America.

The Great Basin bristlecones are scientifically important because of their longevity. Methesula has been considered one of the most ancient living trees since its rings were counted back in 1957. It’s more than 4,000 years old.

When bark beetles attack, they emit what’s called aggregation pheromones, which signal to other beetles that a tree is available. But once the tree is done for – once the bark has been stripped through – beetles emit another pheromone, called an anti-aggregation pheromone, that says “kitchen closed.”

With other pine trees, female beetles lay their eggs inside the tree. Once hatched, their babies eat away at the tree.

That’s not the case with the bristlecones. The trees’ internal moisture pressure pushes out the bark beetles, making it an unsuitable place to hatch their offspring.

For the few bark beetles who manage it, their offspring die very young and rarely make it to adulthood. That's why bark beetles have to use a different host tree, like other smaller pine trees, to produce their brood.

But over the last five years, researchers have been more bristlecones losing their battle with the bark beetles.

Connie Millar, a forest ecologist, saw it firsthand at Telescope Peak in Death Valley National Park five years ago.

“I was absolutely shocked at what I found, which was a large percentage of trees that were dead," she said.

From old-growth bristlecone pine, which can live for millennia, to the younger ones that are just a few hundred years old, these trees were being killed off one by one.

This prompted Millar to call up Barbara Bentz, a research entomologist with the USDA Forest Service. For the next two summers Bentz led a group of researchers in a study of the health of bristlecones in Death Valley National Park and the Great Basin.

What they found pointed to climate change's significant role.

Brown needles on a bristlecones is another sign that bark beetles have damaged the tree. This bristlecone stands on Telescope Peak in Death Valley National Park.

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Courtesy of National Park Service

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The problem: human-caused climate change 

It’s no secret that human actions meant to fuel our society — burning coal, oil, gas, or even flying private jets — are contributing to the climate emergency. That means hotter, drier climates; worse wildfires; major climate swings; and even disappearing coasts. 

“Recent increases in growing degree days with no associated increase in precipitation is causing temperature-amplified tree drought stress, while warming temperatures positively influence bark beetle population growth,” the study states.

Bark beetles evolve to adapt in harsh climates, especially in mountainous environments. In a nutshell: human-caused climate change is making it easier for bark beetles to thrive.

When bristlecones retain moisture, that pressure is used to push out bark beetles. But with prolonged droughts, the roots are not getting much water and there’s a lot of evaporation happening on the leaves.

“It's kind of like not being able to resist a cold because your immune system somehow has been weakened,” Millar said.

Even though the past winter storms helped restore natural reservoirs and dampen the ground, most of California still remains in “moderate to severe drought."

Millar points out that with anthropogenic climate change, we are not only going to have colder winters, but that also hotter summers and even more droughts.

“It's concerning when a living thing that can live 3,000 to 5,000 years is having a mass die-off anywhere,” Wines said. “That's a warning sign.”

How can we save the bristlecones?

There are a couple things we can do to help.

One that’s been studied is spraying the anti-aggregation pheromone on trees. This method only works on a few individual trees, however.

We can also act as citizen scientists. If you’re hiking up to see the bristlecones in Death Valley and see a dying tree, report it to a ranger. Here's what to look out for: stripped bark, large holes and fewer pine needles.

Or, we can just be patient and let nature do its thing. Millar said there’s no doubt that the trees that have survived heavy mortality events like bark beetles have already developed genetic resistance.

She says newer trees will contain genes that are resistant to bark beetles under drier and warmer climates. Sure, it’ll take a couple hundred years for the new trees to grow, but that’s how evolution works.