Secrets Unveiled: The Ice Patches of Beartooth Plateau and Their Hidden Stories

By Diana Setterberg, MSU News Service

BOZEMAN – Scientists at Montana State University report that the frozen remains of a prehistoric forest found 600 feet above the current tree line on the Beartooth Plateau could signal potential shifts within the alpine ecosystem if global temperatures keep rising.

A study detailing this finding was released this week in the journal Proceedings of the National Academy of Sciences. It outlines the insights gained from investigating the remnants of an established whitebark pine forest that developed at an elevation of 10,000 feet approximately 6,000 years ago, when warm-season temperatures in the Greater Yellowstone Ecosystem mirrored those observed during the mid-to-late 20th century.

The forest flourished for centuries until climatic cooling initiated about 5,500 years ago as a result of decreasing summer solar radiation, according to researchers. The drop in temperatures caused the tree line to descend and altered the high-altitude terrain from a forested area to the alpine tundra seen today.

David McWethy, one of the authors of the study and an associate professor in the Department of Earth Sciences at MSU’s College of Letters and Science, stated that subsequent volcanic eruptions in the Northern Hemisphere exacerbated the already declining temperatures in the region. The pine forest quickly became encased in ice, where it has remained preserved until it began to thaw in recent years. McWethy noted that this discovery provided the first evidence from a high-altitude locale indicating the establishment of mature forests upslope during warmer climatic periods.

“This is quite significant evidence demonstrating ecosystem alteration due to temperature increases,” he remarked. “It’s an incredible narrative about how dynamic these ecosystems are.”

The study indicates that ice patches, in contrast to glaciers, do not flow. The authors noted that until recently, these patches have been slowly and almost continuously accumulating ice, “which has allowed conservation of deposited materials such as pollen, charcoal, and macrofossils within their frozen layers.”

McWethy explained that the initiative to examine the Beartooth ice patches for clues about climate and environmental conditions over the past 10,000 years originated from work by Craig Lee, who is currently an assistant professor in MSU’s Department of Sociology and Anthropology. In 2007, Lee retrieved a fragment of a 10,300-year-old atlatl from an ice patch on the plateau, alerting researchers to the preservation of millennia worth of cultural artifacts and environmental data in the adjacent ice layers.

“Most of our most valuable long-term climate records are sourced from Greenland and Antarctica. Discovering ice patches that have endured for such an extended period at lower latitudes within the continental interior is quite significant,” McWethy remarked. The ice patches on the plateau span hundreds of square meters in size, which is relatively small when compared to more substantial ice masses found elsewhere.

In 2016, Lee, McWethy, and Greg Pederson, a paleoclimatologist for the U.S. Geological Survey’s Northern Rocky Mountain Science Center and lead author of the newly published study, received a $100,000 Camp Monaco Prize to collect data regarding environmental transformations and past human activities from the ice patches on the plateau. In 2018, they, along with others, secured a grant from the National Science Foundation to explore additional alpine ice patches in the region to reconstruct the long-term climatic history of the ecosystem and its effects on Indigenous North Americans. McWethy indicated that the NSF-funded research has involved extensive collaboration among tribes, federal organizations, archaeologists, and academics from various universities. The tree line investigation is one component of this larger project.

The researchers assert that examining multiple aspects of the ancient ecosystem was crucial to fully understand the frozen forest’s narrative. Team members, which included both graduate and undergraduate students from MSU, analyzed layers of water isotopes and organic substances in ice cores extracted from the patch, while Pederson collected cross-sections of wood from the ancient trees for radiocarbon dating. Pederson noted that these efforts confirmed that the tree line on the plateau moved upwards in response to regional warming and that the whitebark pine forest flourished for 500 years while climatic conditions remained mild and moist.

“The plateau appears to have been an ideal environment for ice patches to form and persist over thousands of years, documenting crucial data on past climates, human activities, and ecological changes,” Pederson stated.

The findings from the study imply that current climatic circumstances might prompt trees to migrate upslope into regions of the plateau now classified as tundra. Nonetheless, Pederson emphasized that although the study’s outcomes are specific to the site, there are strong correlations to global climate influences on tree line altitudes.

“Growing season temperatures are the primary factor determining tree line height and latitude,” Pederson explained. “However, at specific tree line sites, additional elements such as moisture, wind, snowpack, and human impact can also significantly influence forest structure and elevation limits.”

Due to these factors, it is impossible to predict precisely how future tree line forests on the Beartooth Plateau will appear regarding density, distribution, or species composition; these will depend on the extent of warming, according to McWethy and Pederson. They predict that the tree line will likely ascend as the climate heats, although levels of precipitation will play a crucial role in determining the configuration and range of new forest areas.

The authors of the study, including climate expert and MSU Regents Professor Emerita Cathy Whitlock—who has worked in the Greater Yellowstone Ecosystem for four decades—emphasized that these changes will significantly affect future ecosystems. She and Pederson noted that reduced high-elevation snowpack could impact water availability for irrigation and electricity production downstream. McWethy added that should forests start to emerge in tundra regions, the conditions for fuel could drastically change, potentially heightening wildfire risks.

“This is why studies of historical ecological changes hold importance beyond mere scientific interest,” Pederson articulated. “They carry far-reaching implications for the resources upon which we all rely.”

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