Long-term Study: Bison Facilitate Persistent and Resilient Increases in Grassland Plant Diversity

 

A 29-year study of year-round bison grazing¹ has demonstrated the value of this keystone species in restoring vegetative diversity in a Kansas Flint Hills tallgrass prairie. The study was conducted on the Konza Prairie Biological Station, administered by Kansas State University. Year-round bison grazing was compared to no grazing and to the common practice of seasonal cattle grazing.

Ungrazed plots were dominated by a few grass species, with minimal diversity of other species. Plant species diversity increased with both grazing treatments, especially for forbs (non-grass species). However, with bison grazing, the steady 29-year increase in native plant species was about twice that observed with cattle grazing. Many of the increasing species have been relatively rare and targeted for conservation in Kansas. Nonnative plant species remained uncommon. Bison-grazed communities now include a set of plant species that are nearly absent in the ungrazed and cattle-grazed treatments. Moreover, year-round bison grazing promoted plant communities that were resilient to a 2-year extreme drought.

In this study, the bison pasture was 3.8 square miles, where about 275 bison had free range. The pasture grassland contained a dynamic mosaic of fire frequencies. Our Coalition recommends at least 1000 bison on 100 square miles for rewilding bison and their associated biotic community. Under our recommendation, we expect the response of a plant community to bison restoration will be at least as diverse as in the Kansas study.

This study demonstrates, uniquely with long-term data, a need to reestablish public, wild bison on the Charles M. Russell National Wildlife Refuge, as mandated by Congress, to restore the overall biological integrity of the Refuge.

¹Ratajczak, Z. et al. 2022. Reintroducing bison results in long-running and resilient increases in grassland diversity. Proceedings, National Academy of Sciences 119(36):1-7.

See also, Olson, W. and J. Janelle. 2022. The Ecological Buffalo: On the Trail of a Keystone Species – reviewed here in an earlier News item.