A remarkable discovery in the Rocky Mountains has captured attention worldwide: As alpine ice patches melt due to rising temperatures, researchers have uncovered the remarkably preserved remains of a whitebark pine forest that dates back nearly 6,000 years.

This ancient forest was found on the Beartooth Plateau in northwest Wyoming, part of the Greater Yellowstone Ecosystem. The trees are located about 180 meters (around 600 feet) above the current tree line, at an elevation of roughly 3,091 meters (10,141 feet).

The New Scientist reported:

Trees dating back almost 6000 years have come to scientists’ attention due to ice melting in the Rocky Mountains, offering a “time capsule” into the past

A 5900-year-old whitebark pine forest has been discovered due to the melting of alpine ice in the Rocky mountains. Scientists found more than 30 trees approximately 3100 metres above sea level – 180 metres higher than the present tree line – while carrying out an archaeological survey on the Beartooth plateau in Wyoming.

This “offers us a window into past conditions at high elevations”, says Cathy Whitlock at Montana State University. Whitebark pine (Pinus albicaulis) doesn’t grow at this elevation now, so these ones had to grow at a time when the climate was warmer, she says.

Journal reference:

PNAS DOI: 10.1073/pnas.2412162121

Climate-driven changes in high-elevation forest distribution and reductions in snow and ice cover have major implications for ecosystems and global water security. In the Greater Yellowstone Ecosystem of the Rocky Mountains (United States), recent melting of ahigh-elevation (3,091 m asl) ice patch exposed a mature stand of whitebark pine (Pinusalbicaulis) trees, located ~180 m in elevation above modern tree line, that date to themid-Holocene (c. 5,950 to 5,440 cal y BP). Here, we used this subfossil wood record to develop tree-ring-based temperature estimates for the upper-elevation climate conditions that resulted in ancient forest establishment and growth and the subsequent regional ice-patch growth and downslope shift of tree line. Results suggest that mid-Holoceneforest establishment and growth occurred under warm-season (May-Oct) mean temperatures of 6.2 °C (±0.2 °C), until a multi century cooling anomaly suppressed temperatures below 5.8 °C, resulting in stand mortality by c. 5,440 y BP. Transient climate model simulations indicate that regional cooling was driven by changes in summer insolation and Northern Hemisphere volcanism. The initial cooling event was followed centuries later (c. 5,100 y BP) by sustained Icelandic volcanic eruptions that forced a centennial-scale1.0 °C summer cooling anomaly and led to rapid ice-patch growth and preservation of the trees. With recent warming (c. 2000–2020 CE), warm-season temperatures now equal and will soon exceed those of the mid-Holocene period of high tree line. It is likely that perennial ice cover will again disappear from the region, and tree line may expand upslope so long as plant-available moisture and disturbance are not limiting.