BRETT FRENCH | bfrench@billingsgazette.com | Billings Gazette
For more than 5,000 years, a stand of whitebark pine trees in the Beartooth Mountains were preserved in an ice patch.
During an ancient warm period, the trees had grown at an elevation above 10,000 feet – about 600 feet higher than where the trees now thrive. But cooler summers and volcanic eruptions in Iceland over hundreds of years slowly increased the size of the ice patch, eventually entombing the trees.
With high-elevation ice melting at unprecedented rates leaving the trees uncovered, scientists have now conducted an analysis to provide a greater understanding of how current climate change could affect such environments in the Greater Yellowstone Ecosystem in the future.
New study
Lead author Gregory Pederson, of the U.S. Geological Survey’s Northern Rocky Mountain Science Center in Bozeman, and his colleagues recently published their findings in the Proceedings of the National Academy of Sciences. The study is titled: “Dynamic treeline and cryosphere response to pronounced mid-Holocene climatic variability in the US Rocky Mountains.”
Other authors include: Daniel Stahle, David McWethy, Matthew Toohey, Johann Jungclausd, Justin Martin, Mio Alt, Nickolas Kichasa, Nathan Chellman, Joseph McConnell, Craig Lee and Cathy Whitlock.
“When Forest Service colleagues and I identified this location in 2009, there was only a little wood showing,” wrote Lee, a professor at MSU’s Department of Sociology & Anthropology, in an email. “Significantly more was exposed when we cut the first slabs of wood for analysis with students from Montana State University in 2013.”
Whitlock, director of Montana State University’s Paleoecology Lab, has spent decades examining sediment cores from lakes in the GYE to better understand the ecology of the past. Pederson’s study adds another element to such research, she said.
“Scientists (like me) look to the past for examples of how the Yellowstone ecosystem has responded to periods of warming,” Whitlock wrote in an email. “This amazing discovery provides evidence that treeline is likely to shift upslope with increasing temperatures in the coming decades, so long as high elevations have sufficient moisture.”
Implications
Pederson’s study of the aged whitebark pine trees involved cutting samples from 30 “well-preserved large trees” that were of “extraordinary quality” dated to around 5,500 years before present.
From analysis of the trees, the scientists learned that “at a minimum,” the forest spanned a timeframe between 5,940 years ago to 5,520 years ago. This places the trees within the mid-Holocene – the most recent interglacial period dating back 11,700 years.
“The forest structure, demography, and record of growth preserved in the ice patch likely represents the end of a long period (i.e., several centuries to millennia) of forest expansion,” the study concluded. “This final record of forest expansion at high elevations on the Beartooth Plateau coincides with the rapid growth of the ice patches, although it is possible that small stands of trees persisted for millennia after the ice patches became established.”
With Earth’s temperature continually warming, the study predicted “rapid melting of ice” and the possibility of “treeline expansion throughout the Greater Yellowstone Ecosystem,” Pederson and his colleagues concluded.
“Alternatively, if continued rapid warming results in increased aridity (from reduced precipitation and/or enhanced evapotranspiration) and ecological disturbances (e.g., fire, insect infestation, disease) treeline may be depressed in elevation as it was during the early Holocene,” the scientists wrote.
Each scenario “carries implications for possible future high-elevation hydrologic conditions and water resources.”
Current temperatures, the study noted, already “equal or exceed the estimated mid-Holocene warm-season temperatures when the ice-patch forest stand was present and ice cover was greatly reduced.”
Lee called the study’s findings a great illustration of how “finely tuned and remarkable the analysis of ice patch materials can be.
“Basically, these uniquely preserved samples offer a truly unprecedented look at aspects of climate affecting one of our keystone species — whitebark pine — in our part of the world ca. 5000 years ago,” he added. “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.”
Such research takes years to accomplish, Lee said, crediting the “collegial mindset” of past Forest Service personnel for its success, including Jeff Dibenedetto, Halycon LaPoint, Mike Bergstrom and Kyle Wright.
Related study
The new research builds on a similar study published in 2023 that “analyzed pollen, plant macrofossils, and charcoal” from a 10,400-year-old Beartooth ice patch and in sediment from a 6,000-year-old wetland. Both were located about 3 miles from the preserved whitebark pine forest.
The 2023 study similarly explored the relationship between climate variability and shifts in treeline elevation since the end of the last Ice Age and showed increases in tree pollen about 6,200 years ago and then a colder period from 3,000 to 4,200 years ago.
Such research dates back as far as 2008 when Lee collaborated on a study in the Colorado Rockies of Engelmann spruce trees found melting out of an ice patch. Those trees dated back almost 4,000 years and, like the recent study, documented a time when tree growth occurred at higher elevations than it does today.
Ice treasures
Melting ice patches have revealed other spectacular finds in the Greater Yellowstone Ecosystem, beginning in 2010. That was when Lee found a 10,000-year-old atlatl shaft.
“We didn’t realize until the early 2000s that there was a potential to find archaeological materials in association with melting permanent snow and ice in many areas of the globe,” Lee said back then. “We’re not talking about massive glaciers, we’re talking about the smaller, more kinetically stable snowbanks.”
Arguably the most spectacular ice field find occurred in 1991 when the remains of a 5,300-year-old man were discovered in the Tyrolean Alps. Ötzi, one of several names he was given by combining Yeti with his location in the Ötztal Range, was killed when an arrow was shot into his back, severing an artery.
Lisa Baril, Wyoming-based author of “The Age of Melt: What Glaciers, Ice Mummies, and Ancient Artifacts Teach Us about Climate, Culture, and a Future Without Ice,” visited the Iceman museum for her book.
“I think climate change is one of those things that’s hard for people to wrap their minds around in terms of what it means for their day to day lives,” she told the Billings Gazette in September. “Archaeology is a great way to kind of make that connection for a lot of people.”
Unfortunately, the amazing discoveries of ancient organic materials are in danger of being forever lost as ice patches melt. According to NASA, the past 10 years have been the warmest on record.
“Recent warming across the western United States and globally has substantially transformed mountain ecosystems through reductions in snow and ice, increased fire and insect disturbance, and altered species ranges,” Pederson’s study noted.
Earth’s warming climate is also one factor leading to whitebark pine being listed as a threatened species under the Endangered Species Act. The long-growing trees, the oldest surviving 1,000 years, are found at high elevations in seven western states and two Canadian provinces where its seeds provide an important food source for wildlife, including grizzly bears. The trees also offer shade for snowpack, slowing its melting.
Knowledge base
The recent study builds on a growing base of knowledge regarding climate change in the 22 million-acre GYE. This includes the 2021 publication of the “Greater Yellowstone Climate Assessment,” which Whitlock co-authored.
A study of GYE tree ring data, published in 2021, showed an alarming rate of warming over a relatively short period of time, according to research by dendrochronologist Karen Heeter.
While Pederson’s research demonstrates how high-elevation vegetation can change during climate fluctuations, it also noted another, possibly more ominous, consequence: “the associated implications for high-elevation sourced water resources.”
In western states like Montana, snowmelt provides a key source of drinking water for communities, as well as for agricultural irrigation, fisheries and water-based recreation.
The melting of ice patches also spells the end of an exciting period of high-elevation archaeological discoveries.
“These unique alpine spaces — a de facto repository for past events, be that the growth and demise of forests, or the use of some locations by animals and even humans — are melting,” Lee said. “A brutally constant take home.”
Daniel Stahle, Courtesy photo | Analysis of subfossil whitebark pine (Pinus albicaulis) wood beneath a melting ice patch in the Yellowstone region indicates that a mature forest grew above treeline between 5,950-5,440 calendar year before present when the temperatures were similar to 20th century conditions and cooler than present.
