The melting of glaciers in the Rocky Mountains led to a remarkable discovery: a 5,900-year-old whitebark pine forest, including more than 30 dead trees that were entombed in ice for millennia. Scientists found this previously hidden stand of whitebark pine trees on the Beartooth Plateau in northwest Wyoming at an elevation of 3,100 meters (10,140 feet), which is 180 meters above the current tree line.
The tree line, also known as the timberline, marks the edge of a high-elevation habitat that can support trees; above this invisible marker, conditions are too harsh for trees to grow. Discovering these ancient trees far above the current tree line indicates climatic changes that have affected the region over time, suggesting that the area's climate was once warmer than it is today.
By studying the trees' rings and using radiocarbon dating techniques, researchers determined that the trees lived between 5,950 and 5,440 years ago, during a period of gradual temperature decrease. 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, causing temperatures to drop. Climate models show that the temperature drop 5,100 years ago was caused by continuous volcanic eruptions in Iceland. Around 5,100 years ago, it 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 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," Greg Pederson, a paleoclimatologist for the United States Geological Survey and study lead author, said in a statement. The trees were recently exposed when the ice patch began melting due to hotter temperatures related to human-caused climate change.
"Finding ice patches that have lasted this long in mid-latitude regions is a game-changer," David McWethy, one of the lead researchers and an associate professor at Montana State University, noted. "This discovery is very rare because the remains of this forest were trapped under a stationary ice mass, not under a moving glacier," he added.
These ancient trees could offer insights into past climate conditions and reveal critical clues about the climate's dramatic swings over millennia, providing valuable information about Earth's climatic history. "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," Kevin Anchukaitis, a paleoclimatologist at the University of Arizona who was not involved with the research, according to New Scientist.
By learning more about the region's past climate, scientists say they can more accurately predict the future, and the research may unlock secrets about how ecosystems responded to past climate crises—and how they might react in the future. "Year-over-year records, as well as decadal records and even century-level records are exceedingly important. They provide comparative data points for allowing us to contextualize our more nuanced observations of the current climate that we experience today," Craig Lee, a researcher of environmental archaeology at Montana State University and study co-author.
Whitebark pines grow at high elevations throughout the western United States and Canada. Healthy whitebark pines can live for hundreds of years and sometimes survive up to 1,000 years. They are also battling a pest called the mountain pine beetle and a deadly invasive fungus called white pine blister rust. Today, the whitebark pine is considered threatened under the Endangered Species Act.
These trees play an important role in their high-elevation ecosystems, as they provide shade that helps keep snow cold and stable. They provide food for red squirrels, grizzly bears, Clark's nutcrackers, and many other creatures. If global temperatures continue to rise, scientists expect trees to start growing at higher elevations, so long as they have enough moisture.
According to Cathy Whitlock at Montana State University, the discovery "offers us a window into past conditions at high elevations, as you won't see the Whitebark pine growing there today—this is because the climate was warmer when those trees grew." "Our findings highlight the dynamics and variability of these systems over time," McWethy stated.
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 research team is now racing against time to gather as much information as possible before the ice completely disappears.
"Discoveries like this are incredibly rare," McWethy said.
This article was written in collaboration with generative AI company Alchemiq