At the highest points of the Beartooth Mountains, ancient forests are preserved under patches of ice. Now a team of scientists is resurrecting the ice forests to see what they can tell us about the Greater Yellowstone Ecosystem.
New research published in Proceedings of the National Academy of Sciences explores a forest of more than ancient 30 whitebark pine trees preserved in an ice patch on Beartooth Plateau, just outside the northeast corner of Yellowstone National Park. Scientists studying the trees determined the ice encasing them was between 5,440 and 5,950 years old.
Whitebark pines are an important but threatened species throughout the Greater Yellowstone Ecosystem. The forests preserved under these ice patches are revealing more about humanity’s history and its possible future.
“It was quite a surprise that these ice patches have been around that long,” said Dave McWethy, an associate professor of paleoecology at Montana State University (MSU) and one of the authors of the research. “They preserved mature forests growing all over a plateau where there are no trees today.”
Enduring Ice
McWethy said the ice patch that preserved the whitebark forest is one of several discovered on the Beartooth Plateau. The oldest ice has been dated back to 10,000 years.
“We thought they were snow fields at first,” he said. “You can see some patches of ice at the end of the summer in the Beartooth Mountains, but we didn’t have any idea that some of those patches had endured for 10,000 years.”
However, these ice patches don’t date back to the last Ice Age. Scientists believe they were remnants of a period around 12,000 years ago when the climate of the Greater Yellowstone Ecosystem briefly warmed up after the last glacial period in northwest Wyoming.
The presence of a whitebark pine forest reveals how the high-altitude environment has changed over time. The 5,000-year-old trees were growing in a mature forest, and tree rings revealed several iced-over trees were over 500 years old.
“We can't tell if it was a continuous forest like we see at lower elevations or if there were patches of trees growing in areas with more soil moisture,” McWethy said. “It does tell us that the upslope migration of trees and establishment was very dynamic and changed the whole nature of that ecosystem.”
Pinus albicaulis, the whitebark pine, is one of the highest-elevation pine trees in North America. The ancient trees were preserved over 500 feet above the highest strands of living whitebark pines, which means the now-desolate Beartooth Plateau was warm and wet enough to sustain an entire ecosystem that’s since disappeared.
They Were There
The trees weren’t the only interesting artifacts preserved under the ice. An unexpected but exciting discovery was an atlatl shaft, a prehistoric weapon crafted by Paleoindian hunters.
“Craig Lee with MSU’s Anthropology and Sociology Department found cultural, important, cultural materials emerging from these ice patches,” McWethy said. “The atlatl shaft was over 10,000 years old. Since they’re made of wood, they would have degraded if they hadn't been preserved in ice.”
Bison and bighorn sheep skulls have also been found in the ice, with possible evidence that they were hunted and butchered by Paleoindians. McWethy said these artifacts prove humanity's presence and endurance in the Greater Yellowstone Ecosystem much earlier than many believed.
“We brought members of the Crow, Eastern Shoshone, and Arapaho to these sites and to look at these cultural materials,” he said. “They told us that these areas were used by their ancestors, so the idea that Yellowstone National Park and the surrounding area were devoid of human presence is not accurate.”
While many Indigenous nations have strong cultural connections to Yellowstone National Park, there have always been questions about when and how long they lived there. McWethy said the discoveries from the ice patches reveal that the high-elevation forests were heavily used and might have been occupied year-round.
That makes the existence of these ancient ice patches even more remarkable and valuable for ongoing research, especially in an age where climate is of growing importance to scientists in the Greater Yellowstone Ecosystem.
Panoramic view of the forefield of the ice patch showing the exposed ice surface from extensive melt during the 2024 ablation season. (Photo by Gregory Pederson) 
Aerial image showing the ice patch and ice-patch margin where the whitebark pine trees were sampled (red polygon). (Photo by Joe McConnell) 
Location of the ice patch (TOL) with the mid-Holocene whitebark pine stand relative to the modern treeline site (TAL). The map inset shows the approximate location of the study site (purple circle) within the Greater Yellowstone Ecosystem. (Basemaps from Natural Earth and Google Earth courtesy of Maxar Technologies) 
Illistration at left shows how the forest was covered by ice, then uncovered again. (Cowboy State Daily Staff)
Salvation And Devastation
The International Union for the Conservation of Nature’s Red List of Threatened Species classifies the whitebark pine as endangered. The tree faces several threats, including the fungal disease white pine blister rust, mountain pine beetles, and the loss of viable habitat due to climate change.
The tree's conservation status has been a source of contention, which has kept it off the Endangered Species List in the United States. Gov. Mark Gordon opposed any additional federal protection for whitebark populations in Wyoming, saying "any listing under the ESA is concerning" in 2020.
The discovery of the ancient whitebark pines in the Beartooth ice patches is a source of potential hope and concern, depending on perspective. McWethy said the same factors that could provide a refuge for whitebark pines could have dire consequences for people.
“Today's temperatures and the projections for the next few decades are going to be warmer than when these ancient trees were established,” he said. “This could mean a decrease in moisture that could prevent trees from establishing themselves in certain areas of the plateau, while other areas could see forests being established very quickly.”
Rapid forest growth wouldn’t be bad for the whitebark pine or the multitude of animals, like grizzlies and the Clark’s nutcracker, that use its seeds as a food source. However, a warmer climate at the highest points of the Beartooths would also be drier.
“That has implications for water supply, snowpack persistence, and fire activity,” McWethy said. “If you've suddenly got trees where there are no trees, the nature of fire in these systems can change dramatically in terms of how intense they are, how far they spread, and how many there are. Fire is a very natural part of these ecosystems, but that could be negative for humans.”
A Mammoth Task (With No Mammoths)
The latest research into the ancient whitebark pine forests on the Beartooth Plateau provides an exciting look into the not-too-distant past. According to McWethy, that’s just the tip of the ice patch.
“We've got a list of other ice patches that we want to visit in the next five years,” he said. “Our team submitted a proposal to the National Science Foundation several months ago, and we’re waiting to hear whether we have obtained that funding. The National Park Service has provided funding to explore more ice patches next year.”
Further fieldwork could reveal more ancient forests, animal remains, and archaeological artifacts. Each discovery will help scientists better understand the past, present, and future of the Greater Yellowstone Ecosystem.
However, there's one thing McWethy and his team aren’t expecting to find: remains from massive Ice Age animals.
Fossils from Ice Age mammals are common throughout Wyoming, and intact mammoth, rhino, and lion carcasses can turn up in the permafrost of Alaska and Russia. Nevertheless, scientific evidence suggests these prehistoric creatures were already extinct when the ice patches formed on the Beartooth Plateau.
“We think the last glacial ice melted 12,000 to 14,000 years ago, which is around the time North America’s megafauna went extinct,” he said. “We haven't found any ice patches over 10,000 years old, so it's unlikely their remains would be preserved on the plateau because there was no ice between those periods. But, there’s always a possibility.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
