Ancient forest uncovered by melting ice in the Rocky Mountains

A nearly 6,000-year-old forest is once again seeing daylight after millennia hidden under ice in the Rocky Mountains. 

A team of scientists from Montana State University, the U.S. Geological Survey and collaborating institutions discovered the ancient whitebark pine forest while on an archeological survey on the Beartooth plateau in Wyoming, thanks to warming temperatures that melted the ice previously covering it. 

“We were really surprised to find a forest was emerging from the margins of the ice…. It was amazing,” Cathy Whitlock, a professor in the department of Earth sciences at Montana State University, told As It Happens host Nil Kӧksal.

Whitlock’s team was able to find about 30 trees at about 3,000 metres above sea level, which is 180 metres higher than the existing tree line. Their research was published in the peer-reviewed journal Proceedings of the National Academy of Sciences on Dec. 30, 2024. 

Whitlock says that while it’s an exciting discovery, it’s bittersweet. The only reason they were able to make this discovery is because of the melting ice patch.

“I’m thrilled because it’s a window on the past. It tells us what this high-elevation environment was like 6,000 years ago,” said Whitlock.

“But as a person who worries about the future and climate change and what these alpine areas will look like for my grandchildren, it makes me really sad. These ice patches are melting and they probably won’t be there in a few more decades.”

What they learned

To find out how old the trees were, Whitlock and her team used a tool that certainly didn’t exist when the trees first took root. Using chainsaws to cut out slabs, they were able to carbon date the ancient logs by looking at the rings inside the trunks. 

That revealed that the trees ranged from 5,950 to 5,440 years ago, and also gave them information about the climate the trees would’ve lived in. 

“It was a pretty well-developed forest. These were not the kind of scruffy trees that you see in treeline. These were tall-standing trees,” said Whitlock.

She says about 5,000 years ago, the climate started to cool and an ice patch developed. The ice would’ve killed the trees, leaving them to be buried by the developing ice patch. 

Professor Colin Laroque, who specializes in the age estimation of trees, says this is a startling reminder of how quickly the climate is changing.

“We see how rapid the warming we are experiencing now is happening. What took thousands of years to do in the past, is taking decades to unravel today,” said Laroque, a University of Saskatchewan professor, who wasn’t involved in the study. 

Next steps

This isn’t the first such discovery in North America. In western British Columbia, melting ice has revealed old forests along the Coast Mountains. 

In Wyoming, Whitlock says there’s more work to do. Her team will continue to look through the ice patch, examining the chemistry of the ice to learn how the climate has changed over time.

“There’s a lot that we don’t know about these high-elevation forests and how they’re going to respond in the future,” she said.

Whitlock says what they’ve learned so far shows the power of climate change, and how easily the world can change as the temperature warms or cools. 

“It makes me appreciate how sensitive these high-elevation environments are,” said Whitlock. “We can go from tundra to forest with just a small amount of warming. And so it’s very, very sensitive to climate change.”

She says that as the temperature warms now, this forest may someday return and the current treeline is likely to move to a higher elevation. With it, the area will lose an important source of water. 

“One thing that seems pretty clear is that we’re going to lose our snowpack at high elevations, and that’s simply because it’s warmer. There’s less snowfall. More of the precipitation falls as rain instead of snow and it melts sooner,” said Whitlock.

“As the climate changes, we’re going to lose that source of water and it’s going to just be part of the reason why the West is becoming drier and will continue to dry.”