Kansas research shows reintroducing bison to tallgrass prairie doubles plant diversity

TOPEKA, Kansas — Decades of research by Kansas State University scientists offers evidence that reintroducing bison to roam the tallgrass prairie has gradually doubled plant diversity and improved resistance to extreme drought.

The gains documented in the journal Proceedings of the National Academy of Science were among the largest recorded in the world in terms of species richness in pastures. The research involved more than 30 years of data collected at the Konza Prairie Biological Station near Manhattan.

Zak Ratajczak, principal investigator and assistant professor of biology at Kansas State, said the removal of nearly all prairie bison occurred before quantitative records were established. That meant the effects of removing the dominant grazer were largely unknown, he said.

“Bison were an integral part of the North American grasslands before they were abruptly removed from more than 99% of the Great Plains,” Ratajczak said.

The research took place in the Flint Hills Ecoregion, which is the largest remaining tallgrass prairie landscape. Researchers examined plant composition and diversity on sections of land without mega-grazers, with bison allowed to graze year-round and domestic cattle allowed to graze during the growing season.

“Our results suggest that many grasslands in the central Great Plains have significantly lower plant biodiversity than they would have had before the bison were largely wiped out,” Ratajczak said. “Returning or ‘re-wild’ native megafauna could help restore grassland biodiversity.”

The study confirmed that livestock had a positive impact on plant diversity, compared to the absence of large grazers present. Increases with cattle in plant species richness were significantly lower than those with bison.

In addition to addressing land use, researchers sought to understand how bison influenced plant resilience to climate extremes. Due to the length of the study, researchers were able to capture one of the most extreme drought events to occur on the Great Plains since the Dust Bowl of the 1930s.

“The resilience we found in bison grasslands is also consistent with the idea that diversity promotes ecological resilience,” Ratajczak said. “And that resilience will only become more important if our climate becomes more extreme.”

Other State K biology researchers involved in the study were Jesse Nippert and John Blair, professors; Allison Louthan, Assistant Professor; and Jeffrey Taylor, research assistant. Other contributors included Scott Collins, University of New Mexico; Sally Koerner, University of North Carolina; and Melinda Smith, Colorado State University.

“Some of the most significant ecological trends take decades to develop,” Nippert said. “Without this kind of data, fundamental properties of ecosystems can go unnoticed using only short-term experiments.”

A series of six grants totaling more than $31.6 million since 1980 from the National Science Foundation funded the study and was conducted under the NSF Long-Term Ecological Research, or LTER, program.

“The research done at Konza Prairie is truly unique and impressive,” said David Rosowsky, K-State’s vice president of research. “There are very few places in the world that can provide this kind of long-term data that can have such a strong impact on how we interact with our natural resources.”

Konza Prairie Biological Station is jointly owned by Kansas State University and the Nature Conservancy.