Reintroducing bison results in long-running and resilient increases in grassland diversity

Significance Large animals (megafauna) have cascading effects on populations, communities, and ecosystems. The magnitude of these effects is often unknown because native megafauna are missing from most ecosystems. We found that reintroducing bison—a formerly dominant megafauna and the national mammal of the United States—doubles plant diversity in a tallgrass prairie. These plant communities have few nonnative species and were resilient to an extreme drought. Domesticated megafauna (cattle), which have replaced native herbivores in many grasslands, produced less than half of this increase in plant species richness. Our results suggest that many grasslands in the Central Great Plains have substantially lower plant biodiversity than before widespread bison extirpation. Returning or “rewilding” native megafauna could help to restore grassland biodiversity.