There are few symbols of the American West more iconic than the bison — shaggy giants that once roamed in the tens of millions before being nearly annihilated by European settlers.

A new study published Thursday in Science finds that bringing North America’s largest land mammals back to their ancient stomping grounds is breathing new life into grassland ecosystems, with benefits cascading across the food web.

Scientists have long known bison act as “keystone species,” shaping prairie landscapes through grazing, wallowing and seed dispersal. Previous research has even suggested their vast herds help lock carbon in the soil.

But the latest findings, from Yellowstone National Park, reveal just how dramatic their influence can be for ecosystem health when they are allowed to roam freely thr

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