Recent research from scientists at Washington and Lee University, the National Park Service, and the University of Wyoming highlights the significant ecological benefits of bison recovery efforts in Yellowstone National Park. The research published this week in the journal Science reveals that unique and promising result. These big grazers aren’t just bouncing back, they are proving critical to recharging the park’s ecosystem.
By the late 1800s, bison were driven to the brink of extinction across North America. By the end of 1902, just 23 bison were left in Yellowstone. After many years of collaborative conservation work, the difference is profound. Finally, starting in the mid-2010s, the Great Northern bison population has leveled off at about 5,000 bison. This study aims to better understand the impacts of these recovery efforts, in no small part by the grazing impacts of bison.
Bill Hamilton, a professor at Washington and Lee U., and Chris Geremia, then a researcher with the National Park Service at Yellowstone, were co-first authors of the study. They worked intimately with co-author Jerod Merkle of the University of Wyoming to drive this research. Their on-the-ground work looked in particular at how bison grazing affects nitrogen cycling processes inside the park.
Field experiments conducted between 2015 and 2021 monitored various factors including plant growth, nutrient cycling, soil chemistry, and microbial populations. Those findings showed that bison grazing is in fact beneficial to plant growth. Vegetation in bison-grazed landscapes can be just as healthy and hardy as that found in all but ungrazed landscapes. These plants are 150% nutrient dense.
Hamilton further clarified how bison deeply affect the environment. As they walk in long, slow paths across Yellowstone, they both improve the land’s nutritional quality and increase its carrying capacity. As an example of success, he underscored that the new, large bison herds are creating a big, beneficial impact. Yellowstone’s grasslands are flourishing thanks to their reintroduction.
This study was able to demonstrate the long-distance bison migration as 1,000 travel miles per year on a 50-mile migratory path. This hoofed variation ensures a constantly changing environment that allows for new grasses to take root with different grazing patterns all over the place. Jerod Merkle, who led the study, discusses the benefits of a continent-wide bison migration. He claims it goes a long way toward restoring the ecosystem services that underpin Yellowstone. He was pointing out the ecological process by which bison grazing produced important heterogeneity in the landscape. He said, “Some areas look like very short carpets and then other areas are still just standing.”
Hamilton likened these shifts to ecological changes in other parts of the country. He remarked, “Their grazing probably has direct effects with important cascading effects for other herbivores and for the food web at large, like what happened in the Serengeti when wildebeest had a population recovery.”
This research demonstrates the critical role that bison play in restoring Yellowstone’s ecosystem. It challenges our understanding of traditional bison restoration efforts, which have typically promoted more controlled, domestic-style herds. These findings indicate that large, migratory herds likely play a much deeper role in ecosystem vitality than modern research has come to realize.