Biology Without Borders

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Reintroduction of the Bison

500 years ago, there were 30 million wild bison to be found roaming North America. By the end of the 1800s, there were only a thousand. I won’t go into detail of how that happened because it is a story for another time, but I will show a picture to illustrate just to what extent they were being hunted.

Pile of American bison skulls to be used for fertilizer in the mid-1870s. Image taken from Wikipedia.

Luckily, environmental organizations and dedicated people are trying to repopulate the wild bison in North America. By now, there’s around 20 thousand wild bison roaming public lands in the United States, and over 150 thousand in private property. The Chicago Tribune is reporting another attempt at bison reintroduction in the northern United States.

The state of Illinois has been one of the states that has seen the return of the bison, in October of last year the Nature Conservancy brought 30 bison to the Nachusa Grasslands west of Chicago. It was brought as a conservation herd to help with the restoration of the the prairie, now Illinois wants to reintroduce wild bison to the Midewin National Tallgrass Prairie for the same purpose.

Locations of the two reserves in relation to the city of Chicago, IL. Image taken from Chicago Tribune website.

The Midewin officials aim to restore the tallgrass prairie to its former glory, using the newly reintroduced bison to help restore native vegetation, which in order will help maintain a more suitable habitat for the grassland birds. Since 1997, Midewin has used domestic cattle to graze the grasslands to manage its vegetation, however cattle will graze on just about any plant while bison are selective in their grazing. This different grazing habit will help the bisons create a habitat similar to what it was in the prairie before the bison were hunted out of the area.

The reintroduction of the bison will be a 20 year experiment, it aims to improve the diversity of the prairie’s fauna and flora. The bison will live in fenced off pastures to be watched by visitors and also s├│ the caretakers have an easier time handling them. It will work much in the same way as it does in the Nachusa Grasslands.

It’s too soon to say if the bison are helping with the restoration of the prairie, however the bison are thriving, none have escaped and there are many bison calves being born. If the reintroduction of wolves to Yellowstone in 1995 is any indication, this bison experiment will be a success and the prairies will see a return of the bird species that come to the northern US during spring and also a more diverse flora. The trophic cascade in Yellowstone was much more nuanced, however the bison will surely affect the development of the specific plants necessary for a healthy habitat for the birds natural to the region.

A simple video explanation of the trophic cascade phenomenon in the Yellowstone Park by ‘Sustainable Human’:


For those interested in what happened in Yellowstone, here’s some papers found on Google Scholar:



Henrique Ramalho Martins