Early settlers turned the prairie into cropland, and used its sod to build homes.

When Europeans first reached North America, prairie land covered more than a quarter of the continental US, stretching thousands of miles from Canada to Mexico, and from east of the Mississippi to the Rockies. A complex system of interdependent plants and animals, the prairie once supported some 60 million bison. By 1900, the American westward expansion had virtually wiped out the bison, the prairie and the Plains Indians who once lived there.

In "Prairie Comeback," Alan Alda visits the Nature Conservancy's Tallgrass Prairie Preserve in northeast Oklahoma, where director Harvey Payne and chief scientist Bob Hamilton are seeking to restore the full prairie ecosystem on a 50-square-mile former cattle ranch. They begin with two key ingredients - bison and fire.

Broadleaf plants add to the prairie's overall biodiversity by producing flowers and seeds.

Prairie plants are specially adapted to fire. Their deep root systems help them survive and are even stimulated by a blaze. Bison like to graze on the young tender shoots of grasses that sprout in the aftermath of a burn. This basic interaction is the foundation of the prairie ecosystem. The broadleaf, flowering plants ignored by the bison grow back in force, since they have less competition from grasses. Such plants attract an array of birds, insects and small mammals -- until, after a couple of years, the grasses recover, and the whole process begins again.

With carefully timed and rotating burns, the Natute Conservancy hopes to restore the quintessential American ecosystem to at least this small corner of the Plains.

For more on this topic, see the web feature:
Tataonka: The Spirit Animal