YELLOWSTONE NATIONAL PARK — Yellowstone Volcano Observatory’s (YVO) Feb. 10 Caldera Chronicles column reveals that Yellowstone National Park’s (YNP) geology can be mapped by the area’s vegetation.

Cathy Whitlock of Montana State University writes that the glacial clays in the Lamar and Hayden valleys are rich in nutrients like calcium and magnesium and have high water-holding capacity that favor growth of grassland and sagebrush steppe; these landscapes are known as the “Serengeti of North America” and support large populations of bison, elk, coyotes, wolves and grizzlies. 

But Whitlock also writes that thinner soils with what she calls “intermediate fertility” form on the eastern side of YNP in the Absaroka volcanic province, supporting forests of Engelmann spruce, subalpine fir, whitebark and lodgepole pine. In contrast, the plateaus of central YNP were created from explosive and lava-flow eruptions and have thin, infertile soils that lack critical nutrients and have low water-holding capacity, limiting most conifers except lodgepole pine. 

Whitlock points out that the vegetation shaped by the geology has varied over time due to its additional dependency on climate. Pollen records from lakes in YNP can highlight the influence of geology and climate on long-term vegetation development, per Whitlock. 

As an example, a pollen record from Slough Creek Pond near the confluence of Slough Creek and the Lamar River in the northeast part of YNP shows that following ice recession the clay-rich areas were covered by shrub tundra, when the climate was cool and wet. When temperatures rose, Whitlock confirms Engelmann spruce moved into northern YNP to form a subalpine parkland. With further warming, more trees arrived and a parkland of spruce, fir and whitebark pine developed. 

During the early-Holocene warm period, Slough Creek supported a forest dominated by lodgepole pine and juniper; now, a Douglas-fir parkland is present after establishing about 7,000 years ago when the climate of northern YNP became drier and fire activity increased.

“So, what do we learn from this?” Whitlock writes. “First, is that Yellowstone is a geoecosystem in which the geologic template as well as changes in climate and fire shape vegetation development…In short, Yellowstone would have looked like the rest of the northern Rockies. But to our good fortune, all of these events did transpire and created the Yellowstone geoecosystem that we see today. Geology matters!”

River Stingray is a news reporter with a passion for wildlife, history and local lenses. She holds a Master's degree in environmental archaeology from the University of Cambridge and is also a published poet, dog mom and outdoor enthusiast.