Melting Ice Reveals Remains of 5,900-Year-Old Trees in Wyoming, Uncovering a Long-Lost Forest

A melting ice patch in the Rocky Mountains has revealed the remains of up to 5,900-year-old trees that could offer insights into past climate conditions, according to new research.

Scientists discovered more than 30 dead whitebark pine trees (Pinus albicaulis) that were entombed in ice for millennia, according to a new paper published late last month in Proceedings of the National Academy of Sciences.

They found the previously hidden stand of trees on the Beartooth Plateau in northwest Wyoming, which is part of the Greater Yellowstone Ecosystem. The whitebark pines were lying flat but had been preserved in good condition, suggesting they were rapidly enveloped by ice.

The trees were recently exposed when the ice patch began melting due to hotter temperatures related to human-caused climate change, reports New Scientist’s Taylor Mitchell Brown. In the same area, receding ice patches have also revealed fragments of wooden hunting weapons, including one that was more than 10,000 years old.

“The plateau seems to have been the perfect place to allow for ice patches to establish and persist for thousands of years, recording important information on past climate, human activity and environmental change,” says study lead author Greg Pederson, a paleoclimatologist for the United States Geological Survey, in a statement.

The trees are located 10,140 feet above sea level, which is roughly 590 feet higher than the region’s current tree line. (The tree line, also known as timberline, marks the edge of a high-elevation habitat that can support trees. Above this invisible marker, the conditions are too harsh for trees to grow.) This suggests the region’s climate was once warmer than it is today.

By studying the trees’ rings and using radiocarbon dating techniques, researchers were able to determine that they lived 5,950 to 5,440 years ago. Then, they looked at data from Arctic ice core samples to understand what the climate was like during that time, a period known as the mid-Holocene.

The trees were alive during an era of falling temperatures, which have been linked with ongoing volcanic eruptions. As volcanoes in the Northern Hemisphere erupted, they spewed so much debris into the air that they blocked sunlight from reaching the surface, which caused temperatures to drop.

Eventually, around 5,100 years ago, it seemingly became so cold that the trees at that high elevation could no longer survive. The chilly weather also caused a nearby ice patch to expand and engulf the whitebark pines.

The trees are “a valuable ‘time capsule’ that tells us not only about these mountain forests 6,000 years ago, but about the climate conditions that allowed them to exist,” says Kevin Anchukaitis, a paleoclimatologist at the University of Arizona who was not involved with the research, to New Scientist.

By learning more about the region’s past climate, scientists say they can more accurately predict the future. If global temperatures continue to rise, for example, they expect trees to start growing at higher elevations, so long as they have enough moisture.

“Year-over-year records, as well as decadal records and even century-level records are exceedingly important,” study co-author Craig Lee, a researcher of environmental archaeology at Montana State University, tells the Billings Gazette’s Brett French. “They provide comparative data points for allowing us to contextualize our more nuanced observations of the current climate that we experience today.”

Today, the whitebark pine is considered “threatened” under the Endangered Species Act. These trees face several stressors, including rising temperatures, drought and wildfires. They’re also battling a pest called the mountain pine beetle and a deadly invasive fungus called white pine blister rust.

Healthy whitebark pines can live for hundreds of years—and sometimes survive up to 1,000 years. They grow at high elevations throughout the western United States and Canada, providing food for red squirrels, grizzly bears, Clark’s nutcrackers and many other creatures. They also play an important role in their high-elevation ecosystems, as they provide shade that helps keep snow cold and stable.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.