A Gnarly Situation: High-Elevation Discovery Raises New Questions About Which California Trees Will Survive Climate Change

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Hugh Safford was hiking at 12,657 feet in California’s Sequoia National Park two years ago when he spotted something strange. It was a young Jeffrey pine, a tree that usually occurs farther downhill.

Safford was hiking at treeline, the forest threshold where trees still grow, but fewer and farther between. Only the toughest species can survive the strong winds, heavy snowpack, and freezing temperatures found there.

Safford is a forest and fire ecologist with the University of California Davis Environmental Science and Policy department. He knows subalpine forests are on the leading edges of climate change — and that this Jeffrey pine (Pinus jeffreyi) didn’t belong.

So how had it gotten there? Were there others? And if so, what did that mean?

The answers could portend unexpected competition at California’s treeline — and a rising threat from wildfire.

For people who know their pines, Jeffreys are easy to spot. Each fascicle — that’s a bundle or cluster — has seven needles, whereas California’s high elevations are still dominated by trees with bundles of five.

These high five pines can survive in cold, harsh, windy places where few other trees can. In California they include whitebark pine (P. albicaulis) and limber pine (P. flexilis), along with foxtail pines (P. balfouriana), which are endemic to the state.

Farther south, high in California’s more arid White Mountains, grows the Ancient Bristlecone Pine Forest, home to a Great Basin bristlecone pine (P. longaeva) that’s the oldest individual tree on Earth. At nearly 5,000 years of age, it’s nicknamed “Methuselah” after the longest-lived person in the Bible (at age 969, a mere lad by comparison).

Bristlecone pines mature very slowly. They can take 100 years to reach just a few feet in height. The resulting dense wood is part of their survival strategy. They bend to mighty winds and over time often grow into fantastically twisted — some would say tortured — shapes.

But how do these old souls respond to climate change?

They already live at timberline, generally between 9,800 and 11,000 feet. Bristlecone pines traditionally do well where most other plants do not. As a result, they’re usually a first-succession species, tending to occupy new open ground after fire or other habitat-transforming events. Over the past 50 years, in response to warming temps, they have nudged up into higher elevations. Meanwhile, the low end of the bristlecone range has contracted, where seedlings often find it too hot and dry now to survive.

The snow on California’s highest peaks is melting earlier. Temperatures are hotter. Until Safford’s discovery, scientists thought climate change would cause one of two things to happen in California’s upper reaches: Either the old men of the mountain would hold hands and march uphill together like the Von Trapp family at the end of The Sound of Music, or they’d duke it out for survival.

Bristlecones have encountered some faster-moving limber pines (no spring chickens themselves, reaching up to 2,000 years in age). Until recently it seemed like that’s where the bristlecone’s main competition would come from, as limber pines began to occupy valuable leading-edge real estate, potentially stopping new and future bristlecones from establishing there.

In 2017 Brian Smithers co-authored a study about this leapfrogging effect of limber pines. Smithers, who did his doctoral work at UC-Davis and is an assistant research professor in Montana State University’s Department of Ecology, says limber pines seem to be winning the race to migrate to higher, cooler elevations. But at least they’re close kin to bristlecones.

The Jeffrey pine situation, though, was completely unexpected.

Safford found the Jeffrey pine upstart growing well above its normal range. For now it holds the highest-altitude record for that species — nearly 2,000 feet above previous records.

When he returned with a team last summer to search other peaks for more Jeffrey pines, they found hundreds. Some were as old as 30 and even 40 years, growing younger as they moved uphill.

“Jeffrey was appearing thousands of feet above where it should be,” Safford said. “Now everything is moving uphill, but Jeffrey pines are jumping, and that’s our mystery. We’re looking at the result, without having looked much at causes.”

He has a hypothesis, however.

Climate models predicted that the highest-altitude trees would continue to migrate up mountainsides, climbing — slowly — until they couldn’t climb anymore. And that’s happening. Last summer Safford and his team found three trees above 4,000 meters (13,124 feet), the first trees ever found at that altitude in the U.S. and Canada, outside of the southern Rockies.

But Safford says those models haven’t accounted for the role of seed dispersal by birds and other species. His number one suspects are Clark’s nutcrackers (named for explorer William Clark but slated to be renamed), clever corvids who use their strong beaks to extract pinecone seeds. They often bury them to eat later, serving as accidental gardeners in the process.

“The Clark’s nutcracker is a huge part of the story,” Safford says.

In California these busy birds have a mutualistic relationship with many subalpine trees, whose seeds are a major food source. The birds can remember up to 1,000 caching spots, where they’ve stored away up to 10,000 seeds. Of course, when one bird stows 100 whitebark seeds under their tongue, flies off and buries 10 caches, “they do it in the hope that they can return at some point to consume them,” Safford says. “Germination is a fail for those birds, because they wanna eat those things.”

If a nutcracker buries 10 whitebark pine seeds and the cache is left to sprout, the germination rate is high. By contrast, seedlings from a Jeffrey pine cache germinate in ones or twos. While Safford assumes these caches contain roughly 10 seeds as well, nobody knows for sure.

“No one has ever dug up a [Jeffrey pine] cache because no one has ever tried to follow a Clark’s nutcracker from the Jeffrey pine to the cache.” Not yet, at least.

And if they did, the birds have strategies to thwart potential thieves. “The birds are in a constant battle with rodents, which are always watching to see where the nutcrackers cache food. These birds are so damn smart…” Safford laughs. “Nutcrackers will fake caching. That’s happened to us multiple times, where we ran out to see the cache, and they faked it.”

Still, he assumes the birds are probably caching Jeffrey pine seeds at the same rates as whitebark. “If only one is coming up, it’s probably because germination cues aren’t right for them to germinate,” he says, but adds that those cues — drought, warmer temperatures, less snowpack — are changing.

“What’s astounding,” Safford says, is not that the species is appearing so high up, “but now it’s starting to survive.”

Granted, these novices are growing notably slower at treeline than at lower elevations. Safford breaks off to laugh again, this time at the Jeffrey pines’ predicament.

“They don’t wanna be there. They would much rather be on the shores of (lower elevation) Lake Tahoe. But they can’t control all those cues. Or where they are dispersed!”

He doesn’t think the Jeffrey pines are a threat to their elders — yet. So far none of the high-elevation ones have any cones on them, so they’re not ready to start reproducing on their own in their new home. As it gets warmer, though, that will change.

“Maybe they’ll start making cones in my lifetime,” speculates Safford, who just turned 63. “Then you might see threshold dynamics. Not just the bird moving them upstream, but a sudden explosion. Jeffrey pine will become much more common and make more offspring, then if it’s growing faster, the other trees won’t be able to keep up.”

But that potential explosion is not the one that concerns Safford so much. It’s the explosive relationship between Jeffrey pine and fire.

In recent decades California has suffered more destructive wildfires than any other U.S. state. Safford was senior author on a study published this April that assessed the state’s rate of deforestation from wildfire between 1991 and 2023. The findings weren’t pretty. During those years, the Golden State lost roughly 8-9% of its conifer forests to wildfire.

Recent megafires have turned large expanses once covered in forest into fields of shrubs or grass. The blazes were simply too hot for conifers to regenerate, and Safford’s study found that efforts to replant California’s forests aren’t keeping pace with their losses.

“For lower-elevation forests, there’s a strong but linear increase of forest being lost to fire,” Safford says. “For high-elevation forests, the rate of increase has been strongly exponential. It’s just brutal.”

Jeffrey is a fire survivor. Like ponderosa pines (collectively “yellow pines”), its thicker bark protects young trees from fire damage, its thick cone scales insulate seeds against heat, and it self-prunes over time. By dropping its lower branches, a Jeffrey pine protects its canopy (where photosynthesis happens) from surface fuels. By contrast, the high-fives and other subalpine trees aren’t nearly as well protected for fire. Up until now, they haven’t needed to be.

“Lightning hits a bristlecone pine and it’s almost impossible for a real fire to start,” Safford explains. “They’re very scattered, there’s no connection of fuels on the ground. Bristlecones and other subalpine trees are slow-growing, with short needles, widely spaced, not a whole lot of litter, [and] compact litter beds that hold moisture and are hard to burn.”

The Jeffreys’ new neighbors “support highly flammable foliage,” Safford says, “which promotes fast, low intensity burning along the ground surface. This type of burning is much more likely to kill the less fire-tolerant competitors of the yellow pines than the yellow pines themselves.”

It’s not that these old men of the mountain will disappear tomorrow. For one thing, the southern Sierra “is so darn high,” Safford says, some peaks can still accommodate upward movement. So although the climate’s warming and changing quickly, it’ll be “multiple lifetimes of humans before a lot of this stuff transpires.”

Not so with fire. California has seen huge impacts from it already, and the Jeffrey pine is both fire-adapted and drought tolerant.

“It’s gonna be the survivor when you filter all these species out,” Safford says. And now, Jeffrey pines are being distributed “all over the landscape. They’re moving all over because the climate is permitting it, creating fuel beds and dense forests that didn’t exist before.”

In other words, Jeffrey pines are not only fire survivors, but fire purveyors.

The pairing of Clark’s nutcrackers with Jeffrey pines isn’t one that climate models foresaw or remote sensing detected. No satellite or artificial intelligence identified these facts. Instead it was quite literally “shoe leather” science: Safford stumbled on his first prophetic Jeffrey pine while out on a hike.

And this summer Safford and his team will be back, climbing more California peaks to do more on-the-ground fieldwork. Thanks to Smithers’ own shoe-leather observations, they know there’s a population of Jeffrey pines in the White Mountains, so they plan to spend a week in that high range where the bristlecones grow.

While Smithers agrees that fire is a concern, he thinks it’s a short-term one.

“I think in any time of transition, as these trees are [moving] farther upslope, a change in habitat occurs and fire is one of those changes.” He’s a big fan of letting fires back into the system naturally — counteracting a century of fire suppression — but he also thinks we need to be OK with our forests changing.

“I have a more long-term philosophical bent on this,” Smithers says. “We humans really don’t have an amazing track record with trying to figure this stuff out anyway. Nature’s gonna have to figure it out.”

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