Uncovered white bark pines
Gregory Pederson
A 5,900-year-old whitebark pine forest has been discovered in the Rocky Mountains as a result of melting alpine ice. Scientists found more than 30 the trees approximately 3100 meters above sea level – 180 meters above the present tree line – while conducting an archaeological survey on Wyoming’s Beartooth Plateau.
This “gives us a window into the conditions of a bygone era,” he says Cathy Whitlock at Montana State University. Whitebark pine (Pinus albicaulis) do not grow at this height now, so they must have grown in a warmer climate, he says.
To understand the history of the lost forest, Whitlock’s team analyzed their rings and used carbon dating to age them. They found that the trees lived between 5950 and 5440 years ago, at a time when temperatures were constantly dropping.
Data from ice cores in places like Antarctica and Greenland suggest that these temperature drops were influenced by centuries of volcanic eruptions in the northern hemisphere. These created enough airborne sediment to cut off sunlight and lower global temperatures the environment it was too cold for these tall trees to survive.
While flattened, the newly discovered trees are in exceptional condition, indicating they were preserved quickly after death. Although there is no evidence of avalanche coverage, they do show markings consistent with the extent of the current ice patch.
Climate models suggest that more volcanic eruptions in Iceland 5,100 years ago caused a further drop in temperature, the team member says. Joe McConnell at the Nevada Desert Research Institute. These lower temperatures spread ice patches and “ensured that fallen trees would be buried in ice and protected from the elements for the next 5,000 years,” he says.
Only in recent decades has the temperature risen enough to free the trees from their frozen crypt. The current tree line “is likely to shift upslope as temperatures rise in the coming decades,” Whitlock says.
“This discovery was made possible by anthropogenic climate change; rising temperatures are now exposing areas buried by ice for millennia,” he says. “While findings like these are scientifically interesting, they are also a sad reminder of how fragile alpine ecosystems are to climate change.”
“The research is a very elegant and careful use of a valuable time capsule that tells us not only about these mountain forests 6,000 years ago, but also about the climatic conditions that allowed them to exist,” he says. Kevin Anchukaitis at the University of Arizona.
These trees are not the first discoveries that researchers have made from Rocky Mountain ice chunks. Previous work found “fragments of wooden shafts used to make arrows and darts,” Whitlock says. One shaft was radiocarbon dated to more than 10,000 years ago, “telling us that people have been hunting in high-elevation environments for millennia,” he says.
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