About 120,000 years ago the world was entering the last Ice Age. The ice sheets were expanding across Montana and the Yellowstone Plateau. But sagebrush, sunflowers and pigweed flourished near modern-day Lovell. The sagebrush sea was far denser in the Bighorn Basin then and it fed mastodons, mammoths and camels.
Researchers know very little about the composition of ancient plant communities in most of North America. But thanks to Wyoming’s Natural Trap Cave — which has preserved one of the best records of ancient flora in the world — scientists can describe plant history in northern Wyoming back about 130,000 years, said Thomas Minckley, an associate professor of geography, paleoecology and conservation specialties at the University of Wyoming.
Minckley is analyzing pollen recovered from the site. With samples collected in 2015 he’s able to recreate the ancient plantscape.
Forests grows and die. Scientists can study how a landscape changes, but the pollen in the cave offers a larger-scale view, he said.
“We can look at environmental processes on time scales we can’t live,” Minckley said.
Minckley extracts environmental history from the dust and other particles that fell into the cave tens of thousands of years ago. When Minckley looks at the pollen he sees a record of plants migrating across the landscape. He can watch the ebb and flow of grasses and trees, thriving and disappearing over thousands of years.
“This is the history of place,” Minckley said. “This is the history of where we live.”
Natural Trap Cave acts, as its name implies, as a trap. When something makes it over the opening, gravity pulls it in and there’s no escape. Nothing grows in the cave, but it serves like a refrigerator for whatever falls inside, Minckley said. Its conditions are perfect for preserving pollen brought in by the wind, or on the fur of a doomed animal.
Pollen grains are water- and decay-resistant and designed by nature to spread genetic material, Minckley said. The pollen he recovered in the cave was well preserved. He can fix the grains in time by dating the volcanic ash it was found with and considering the chronology of vegetation shifts.
In analyzing the plant record from the cave, Minckley can watch the landscape change. He can see the sagebrush contract and expand over millennia. He can see forests arrive and grasslands retreat. It might not seem like it, but its dramatic, he said.
About 25,000 years ago, as the ice sheets made their final expansion, grasslands crept in on the sagebrush and the vegetation was diverse, Minckley said.
Less than 15,000 years later, the grasslands disappeared and forests began to flourish around the basin, Minckley said. They were comprised mostly of pine, but some spruce and Douglas fir were also mixed in. The forests were far more diverse than Minckley imagined. The forests expanded from the base of the mountains upward into the Bighorns, building a landscape that 12,000 years ago, looked very much like what we see today.
His research shows the resiliency of the ecosystem and the plants that still exist, he said.
The information encoded in the pollen has modern applications as well. For example, Minckley can examine which plants were most successful during long droughts, and what happened to the vegetation overall, to inform predictions on how current conditions could shape the future landscape, he said.
Sagebrush and pine trees might seem less glamorous in a world of dire wolves, lions and the American cheetah. But Minckley’s research looks at how the diversity in the plant community related to the animals that roamed Wyoming tens of thousands of years before.
“There are layers of complexity to understand the biodiversity of what was,” he said.
And though it may be tough to imagine a short-faced cave bear, people know what the plants looked like thousands of years ago, because they are the same as what we see today, Minckley said.
Minckley likes to sit on a hill, take in the trees and grasses and think about how the environment has changed over thousands of years.
“We’re not moving continents,” he said. “This isn’t deep time geology where mountains are lifting and the state is covered by an inland sea. This is how the vegetation we experience today came to be. By analyzing these records, we are basically sitting on the foothills in the Bighorn Mountains and watching the waves of plant communities move around you. And that’s pretty cool.”