A new study published in the journal Science suggests if land managers want to improve ecosystem health, it would help if bison are present across a greater swath of land.
Its publication comes amid a lawsuit filed by the state of Montana that seeks to cut Yellowstone National Park’s bison herd in half.
The study measured carbon and nitrogen dynamics and followed the eating patterns of large bison herds in Yellowstone over a period of seven years. Scientists monitored 16 sites with differing conditions and elevations.
One of the study authors, Jarod Merkle, who is a professor of migration ecology and conservation at the University of Wyoming, says a common conception is that bison overgraze in Yellowstone. But he said there’s more than what meets the eye. When bison eat plants and pee and poop, that releases nitrogen, and when plants are bitten off, that releases nutrients.
“ There's this amazing ecosystem in the soil going on, so there's more nitrogen in the soil. The microbe activity is off the charts, and that all provides better quality nutrients like fertilizer for the plants themselves to grow again,” he said.
Merkle said the effect is more nutritious, high protein food for bison and other animals to munch on.
The study found that bison grazing led to 156% more crude protein in lawn-forming habitats, 155% more in high elevation areas and 119% more in dry habitats.
While bison reintroduction has been accelerating in recent years, many of the animals are confined to limited geographic areas in state parks, ranches and other areas.
“ There's a lot of bison restoration going on right now, and it's all excellent. It's really exciting. But a lot of those restoration efforts are small bison herds that are constrained to smaller areas. And what our study shows is that we're not gonna see quite the ecosystem effect in that type of bison restoration without allowing their numbers to get bigger and allowing them to naturally migrate and move across a landscape,” he said.
Montana’s lawsuit seeks to cap Yellowstone’s herd at 3,000 animals over worries that bison migrating outside of the park could infect cattle with a reproductive disease called brucellosis and other concerns. Last year the park approved a 10-year management plan to allow the herd to grow up to 6,000 animals. The park’s been averaging about 5,000 animals for the past decade.
