Scientists spent 6 years following the great migration of Yellowstone bison. What they found is remarkable
Bison almost disappeared from North America at the end of the 19th and early 20th century. But conservation efforts in recent decades have seen figures gradually increase, especially in Yellowstone National Park where around 5,000 animals now live.
These huge herbivores travel around 1,000 miles each year while they move back and forth along a 50 mile migration route across the park. But how do large migratory herds such as those of the landscapes of Yellowstone are fit and that their effects improve or degrade ecosystems?
This is what researchers from Washington and Lee University, the National Park Service and the University of Wyoming wanted to discover it. Thus, they spent six years following the animals when they moved through the seasons, using experiences in the field, satellite images and GPS collar data to compare pastured and un loose plots.
The results of their study, recently published in the journal ScienceSuggest that the Yellowstone bison reshaves the park’s ecosystems in a largely positive way – creating a patchwork of habitats, which improves biodiversity while keeping healthy floors.
How do the bisons improve the ecosystems exactly?
While the great herbivores are concentrated in the river valleys in the spring and summer, they are strongly feeding on new shoots, creating landscapes which seem to be overgrazed but are in fact the opposite, explains Bill Hamilton, professor at Washington and at Lee University.
“What we are witnessing is that when bison move through the landscape, they amplify the nutritional quality and the ability of Yellowstone.
“Their grazing probably has important consequences for other herbivores and for the food network as a whole, similar to the changes that occurred in the Serengeti when the Gun population has recovered.”
By consuming young plants, bison accelerates the nitrogen cycle. Soil microbes increase, recycling more nitrogen in shapes than plants can use. The result is the grasses that push as much as those without victory but which are 150% more nutritious, explains Hamilton, who says that these advantages go outside, supporting other animals and enriching the whole food canvas.
“With the current big herds of bison, Yellowstone’s meadows work better than in their absence,” explains Hamilton. “And this version is an overview of what was lost when the bison was almost wiped out in North America in the late 1800s.”
Jerod Merkle of the University of Wyoming agrees. “The return of a large-scale bison migration offers clear advantages to the ecosystem services that underlie Yellowstone,” he said. “Heterogeneity is the bison to provide. When I look through the migration of the bison, there is a strong variation in the quantity of pasture – some places seem to be very short lawns while others remain intact.”
Unlike closed or managed populations, the Yellowstone bison shows that freedom of movement is at the heart of the ecological advantages they bring to landscapes, concludes the study.
Image of the top: bison grazing near Roosevelt Arch in the spring. Credit: Jacob Frank | National Park Service
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