Why trees are reaching new heights in the mountains

California’s Sierra Nevada range is known for its rugged peaks, vast wilderness, and iconic trees. For centuries, botanists and hikers alike have climbed these mountains, encountering the same types of conifers as they ascend in elevation – lodgepole, foxtail, and limber pines staking their claim in the uppermost zones of tree life.

But sometimes, nature throws a curveball. In the fall of last year, a routine hike in Sequoia National Park turned into a rare discovery. Professor Hugh Safford of UC Davis was not searching for scientific revelations.

He was simply out for a walk in the mountains. Yet what Professor Safford found has rewritten the elevation record books and raised urgent questions about how trees are responding to climate change.

His discovery, now published in Madroño, a journal of the California Botanical Society, is a glimpse into the High Sierra’s changing face – and a reminder of the power of simply being present in nature.

A tree where it should not exist

Safford, a forest ecologist in the UC Davis Department of Environmental Science and Policy, had paused during his hike along the timberline on the south slopes of Mount Kaweah.

He admired a foxtail pine, then a lodgepole pine – both expected residents of the subalpine zone. But then, something unexpected caught his eye.

“Then I thought, ‘What’s that?’” said Safford. “I walk over, and it’s a Jeffrey pine! It made no sense. What is a Jeffrey pine doing above 11,500 feet?”

Jeffrey pines typically dominate the upper montane forests of the Sierra Nevada. They’re the common backdrop around Lake Tahoe and Mammoth Lakes.

But they are not known for living among the rugged, wind-battered zones of traditional subalpine species. What Safford found was extraordinary: a healthy Jeffrey pine growing far above its expected range.

Jeffrey trees break mountain height records

After that first encounter, Professor Safford began looking more closely. Over the course of his hike, he identified 14 Jeffrey pine trees thriving above 11,800 feet. Some were over 20 years old. The highest of them stood at 12,657 feet. That shattered the previous known elevation record for the species by 1,860 feet.

Even more surprising, these pines were growing higher than any of California’s traditional subalpine species, including the foxtail, limber, and lodgepole pines. Until now, none of those species had been documented above 12,034 feet.

Safford’s field observations suggest that our existing databases, satellite data, and models may be significantly underestimating where certain tree species are managing to survive.

Trees grow higher up mountain slopes

Why are Jeffrey pines now taking root at elevations once deemed too extreme for their survival?

The answer, Safford suspects, lies in the warming climate. Rising air temperatures and earlier snowmelts are reshaping the ecological dynamics of the High Sierra.

The high mountain soils, once locked under snow for months, are thawing earlier. This opens short windows of opportunity for seeds to germinate and grow. In this altered climate rhythm, some species are seizing the chance to move upward.

The Jeffrey pine’s tolerance to both cold and drought may be key to its success in these harsh new environments. But trees don’t move on their own. Something – or someone – has helped them get there.

Birds, trees, and mountain heights

Safford suspects that the Clark’s nutcracker, a high alpine bird with an excellent memory, may be playing an unexpected role in this ecological shift.

Known for its relationship with the whitebark pine, the bird collects seeds and stores them in high mountain “caches” for future meals. For Jeffrey pines, the bird might be acting as an unintentional gardener.

“Much as this nutcracker does for whitebark pine trees, preliminary evidence suggests the bird carries fleshy Jeffrey pine seeds up the mountain from thousands of feet below, storing them in the High Sierra’s ‘refrigerator’ for an early summer snack.”

Some of those snacks never get eaten. And when the conditions are right – less snow, warmer soil – those seeds take root and start a new population.

Trees aren’t migrating slowly

Trees generally move slowly in response to climate change. Their range shifts inch upward over decades. But Safford’s discovery hints at a more chaotic process, influenced by outside forces like birds and sudden environmental windows.

“I’m looking at trees surviving in habitats where they couldn’t before, but they’re also dying in places they used to live before,” Safford said.

“They’re not just holding hands and walking uphill. This crazy leapfrogging of species challenges what we think we know about these systems reacting as the climate warms.”

This leapfrogging defies the gentle, predictable march that many models assume. It reveals a more fragmented and opportunistic reality, where chance encounters between birds and seeds create new ecological frontiers.

Mountain trees reaching new heights

Perhaps one of the most telling aspects of Safford’s discovery is how it happened. Not through satellite imagery. Not through remote sensors or AI-driven models. But by someone walking in the mountains and paying attention.

“People aren’t marching to the tops of the mountains to see where the trees really are,” Safford said. “Instead, they are relying on satellite imagery, which can’t see most small trees. What science does is help us understand how the world functions.”

”In this case, where you see the impacts of climate change most dramatically are at high elevations and high latitudes. If we want our finger on the pulse of how the climate is warming and what the impacts are, that’s where it will be happening first. We just need to get people out there.”

A story of resilience

Safford and his team of students will return this summer to the southern Sierra Nevada. They’ll hike Mount Kaweah, Mount Whitney, and nearby parks, searching for more of these high-altitude outliers.

Their work will include identifying seedlings, measuring mountain tree heights, and refining elevation models based on actual ground conditions.

The mission is simple: understand what’s happening before more changes go unnoticed. The Jeffrey pine may not remain the state’s highest tree forever, but for now, it tells a story of change, resilience, and the surprising ways life finds new ground.

The study is published in the journal Madroño.

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