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Bison can restore animal diversity and ecosystem health

Land managers have been working to restore the health of the Great Plains ecosystem through the widespread reintroduction of bison. A new study suggests that these efforts are paying off. The experts report that grazing by bison has restored bird diversity and improved the overall health of a mixed-grass prairie in Montana.

Study lead author Andy Boyce is a conservation ecologist at the Smithsonian National Zoological Park and the Conservation Biology Institute’s Migratory Bird Center.

“We’ve known for some time that bison don’t spend as much time in wetland areas as cattle do, but what we didn’t understand was how this difference was going to influence biodiversity,” said Boyce. 

“When we looked at areas where bison were reintroduced, and compared them to similar areas with cattle, we found that the  vegetation along small streams changed in ways that are associated with more diverse bird communities and increased use of these areas by native ungulates like white-tailed deer.”

“Bison reintroduction is resulting in healthier more biodiverse riparian environments, which is great news for tons of other prairie species.”

The researchers explained that grazing by large herbivores in grassland ecosystems affects biodiversity by modifying the vegetative environment through selective consumption. To investigate whether restoration of bison is associated with increased bird diversity within a temperate grassland ecosystem, the experts focused on a mixed-grass prairie in northcentral Montana. 

“We used a long time-series of remote sensing imagery to examine changes in riparian vegetation structure in stream networks within bison and cattle pastures. We then assessed how vegetation structure influenced diversity of bird communities and detection rates of mammals in these same riparian networks,” wrote the study authors.

“We found that percent cover of woody vegetation, and native grasses and forbs increased more rapidly over time in bison pastures, and that these changes in vegetation structure were associated with increased bird diversity and cervid occupancy.”

According to the researchers, the findings indicate that replacing cattle with bison could have positive impacts on vegetation and mammals.

“Furthermore, we predict that increases in riparian vegetation will be associated with increased diversity of bird communities,” wrote the study authors.”We also predict that deer use will increase with higher shrub and tree cover after accounting for distance to the Missouri River drainage, a forested landscape that serves as a source population for cervids.”

By Chrissy Sexton, Staff Writer

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