Yellowstone National Park’s American bison are truly a sight to behold. The only population of free-ranging buffalo in the lower 48, they number over 4,000 strong and remain a powerful tourist draw. Bison were famously pushed to near-extinction in the 19th century, and only recently sprang back to healthy numbers.
But the rapidly increasing size of Yellowstone’s bison population has some worried about the long-term stability of the park’s grasslands. Syracuse University biologist Douglas Frank, who has examined the effects of climate change and herbivores on Yellowstone’s grasses for two decades, plans to embark on an extensive study to assess the bison’s impact.
“During the late 1980s, similar concerns were raised about the size of the park’s elk herd and whether the herd was negatively impacting grasslands,” says Frank, according to Syracuse University’s website. “Rather than having a negative impact on the grasslands, we found that increases in elk grazing actually stimulated plant growth.”
Frank, a professor in Syracuse University’s College of Arts and Scientists, plans to spend three years on the project. He will work with the National Park Service to monitor the herds’ grazing habits, using research methods he developed in his 20 years studying the park’s grasslands.
“Fossil records indicate that prior to the industrial revolution, the Earth’s grasslands and large herds of migratory herbivores coexisted for millennia,” Frank says. “These systems were stable, despite having sustained very intense levels of grazing. My work in Yellowstone explores why and how this happens.”
In Frank’s previous work on elk grazing habits, he found that several factors contributed to plant growth. For one, elk feces and urine in grazing areas provided ample fertilizer for plants. The intensive feeding also stimulated plants to grow new shoots and leaves, enhancing the overall health of the grasslands.
“Heavy grazing also increases the amount of nitrogen in the leaf material, which increases the quality of material that falls to the ground,” Frank says. “The high-quality litter is quickly broken down by soil bacteria, which in turn enriches the soil around grazed plants.”
Regardless of the outcome, the study will provide scientists with further insights into Yellowstone’s ecosystem.
“We also intend to use this opportunity to better understand the complex and fascinating ways in which the interactions among plants, herbivores, and soil organisms foster the stability of grassland systems,” Frank says.