Yellowstone's free-moving large bison herds provide a glimpse of their past ecosystem function

Although momentum is building to restore bison across North America, most efforts focus on small, managed herds, leaving unclear how large, migrating herds shape landscapes and whether their effects enhance or degrade ecosystems. We assessed carbon and nitrogen dynamics across the northern Yellowstone ecosystem, where one of the last remaining large migratory populations resides. Bison stabilized net aboveground production while accelerating nitrogen turnover, increasing aboveground nitrogen pools while carbon pools remained stable, which improved landscape nutritional quality. Effects were strongest in wet, nutrient-rich habitats that received higher bison densities and grazing than is recommended in rangeland management, while soil and plant conditions suggested landscape resilience. Restoration should embrace heterogeneity in densities and effects across habitats and spatial scales beyond those guiding most current recovery efforts.