Scientists have discovered frozen remnants of an ancient forest located 600 feet above the present tree line on the Beartooth Plateau, which could signal significant changes to the alpine ecosystem if global warming continues.
Scientists have discovered frozen remnants of an ancient forest located 600 feet above the current tree line on the Beartooth Plateau, which may indicate potential changes to the alpine ecosystem if climate change persists.
A research paper detailing this finding was published in the journal Proceedings of the National Academy of Sciences. It reports on the study of the remains of a mature whitebark pine forest that existed at an elevation of 10,000 feet approximately 6,000 years ago, during a period when temperatures in the Greater Yellowstone Ecosystem were comparable to the mid-to-late 20th century.
The forest thrived for centuries until a cooling trend began about 5,500 years ago, attributed to reduced summer solar radiation, which led researchers to observe that the tree line moved downward and transformed the previously forested area into the alpine tundra we see today.
David McWethy, an associate professor in MSU’s Department of Earth Sciences, explained that additional volcanic activity in the Northern Hemisphere caused even further cooling of the region. This led to the quick encasement of the pine forest in ice, where it remained well-preserved until recent thawing. McWethy noted that this discovery provided the first evidence from an alpine region that mature forests once grew at higher elevations when the climate was warmer.
“This is compelling proof of how ecosystems change in response to temperature increases,” he stated. “It’s a remarkable narrative showcasing the dynamic nature of these systems.”
The paper also mentions that ice patches, unlike glaciers, do not have a flow. Until recently, the researchers noted, these ice patches gradually accumulated ice, which helped preserve materials like pollen, charcoal, and macrofossils in their frozen layers.
McWethy explained that the initiative to investigate Beartooth ice patches for insights about climate and environmental conditions dating back 10,000 years stemmed from groundwork by Craig Lee, now an assistant professor in MSU’s Department of Sociology and Anthropology. In 2007, Lee discovered a 10,300-year-old atlatl in an ice patch on the plateau, highlighting the potential preservation of millennia’s worth of cultural artifacts and environmental data in adjacent ice layers.
“Most of our long-term climate records originate from Greenland and Antarctica. Finding ice patches that have endured for so long at lower latitudes within the interior of the continent is significant,” McWethy added. The ice patches on the plateau are several hundred square meters, which is relatively small in comparison to larger ice formations elsewhere.
In 2016, Lee, McWethy, and Greg Pederson, a paleoclimatologist with the U.S. Geological Survey’s Northern Rocky Mountain Science Center and lead author of the published paper, received a $100,000 Camp Monaco Prize to gather data on environmental changes and ancient human activities from the plateau’s ice patches. By 2018, they secured a grant from the National Science Foundation to study other alpine ice patches in the region and reconstruct the long-term climate history of the ecosystem and its impact on Indigenous North American communities. McWethy mentioned that this NSF-funded research involves collaboration with tribes, federal agencies, archaeologists, and various university scientists, with the tree line study being one aspect of the project.
The research team stated that it was essential to analyze various components of the ancient ecosystem to fully understand the frozen forest’s history. Team members, including both graduate and undergraduate students from MSU, studied layers of water isotopes and organic substances in ice core samples from the patch, while Pederson extracted wood cross-sections from the ancient trees for radiocarbon dating. Pederson indicated that their findings verified that the tree line on the plateau had shifted upward due to regional warming and that the pine forest thrived for 500 years under moderate and moist climatic conditions.
“The plateau appears to have been an ideal location for the formation and longevity of ice patches, maintaining crucial records of past climate, human activities, and environmental changes,” Pederson stated.
The study’s findings suggest that current climate changes could result in trees migrating upward into areas of the plateau that are currently tundra. However, Pederson emphasized that while the study results are specific to this site, there are significant connections to the global climatic factors influencing tree line elevations.
“Growing season temperatures play a key role in determining tree line elevation and latitude,” Pederson explained. “However, at specific tree line locations, additional factors such as moisture levels, wind conditions, snowpack, and human activities may significantly influence forest structure and elevation limits.”
Due to these factors, it is challenging to predict precisely how future forests at the Beartooth Plateau will appear in terms of species diversity, density, and overall distribution, as these will depend on the degree of warming, according to McWethy and Pederson. They anticipate that the tree line will likely rise with climate warming, but precipitation will also play a crucial role in shaping the structure and extent of new forests.
The study authors, including climate specialist and MSU Regents Professor Emerita Cathy Whitlock, who has studied the Greater Yellowstone Ecosystem for 40 years, warn that these changes could have significant repercussions for the future ecosystem. Both she and Pederson noted that reduced snowpack at high elevations could impact water resources for irrigation and electricity generation. McWethy added that if forests were to start growing in tundra areas, conditions could alter dramatically, potentially increasing wildfire risks.
“This is why researching past ecological changes is more than just fascinating science,” Pederson concluded. “It has broad implications for the resources we all rely on.”
