Reintroduction of bison to grasslands increases plant diversity, drought resistance

A study led by Kansas State University has found that reintroducing bison — a formerly dominant grazer — doubles plant diversity in a tallgrass prairie. The research spans more than 30 years of data collected at the Konza Prairie Biological Station and was recently published in the journal Proceedings of the National Academy of Science, or PNAS.

The study found that plant communities also withstood the most extreme drought in four decades. These gains now rank among the largest recorded increases in species richness from grassland grazing worldwide, researchers said.

“Bison was an integral part of North American grasslands before they were abruptly removed from more than 99% of the Great Plains,” said Zak Ratajczak, assistant professor of biology and principal investigator. “This removal of bison occurred before quantitative data and therefore the effects of their removal are largely unknown.”

The study took place in the Flint Hills ecoregion, the largest remaining landscape of the tallgrass prairie. Researchers examined the composition and diversity of plant communities in three treatments designed to capture characteristic management regimes: there were no megagrazers; bison were reintroduced and allowed to graze year round; or domesticated cattle were introduced and allowed to graze during the growing season.

“Our results suggest that many grasslands in the central Great Plains have significantly lower plant biodiversity than would have been the case before large-scale extermination of bison,” Ratajczak said. “Restoring or ‘wilding’ native megafauna could help restore grassland biodiversity.”

The study also found that livestock had a positive impact on plant diversity, compared to the lack of large grazers, although the increase in plant species richness was significantly smaller than that caused by bison.

“I think this study also shows that livestock can have a largely positive impact on the conservation of biodiversity in our region, especially given that many in the livestock industry are feeding the prescribed fires that have prevented these grasslands from becoming forests. said Ratajczak. “What this study really suggests is that when economically and environmentally feasible, reintroducing bison could have an even more positive impact on biodiversity conservation.”

In addition to addressing land use, researchers also wanted to learn how bison affect the resilience of plant communities to extreme climate changes. The long duration of the study allowed researchers to capture one of the most extreme drought events to occur in the Great Plains since the Dust Bowl of the 1930s.

Researchers found that native plant species in the bison-grazed area could withstand drought after the extreme climate.

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

Other K-State researchers in the study include Professor Jesse Nippert; John Blair, college professor; Allison Louthan, assistant professor; and Jeffrey Taylor, research assistant, all of the Department of Biology at the College of Arts and Sciences. Other contributors include Scott Collins, University of New Mexico; Sally Koerner, University of North Carolina; and Melinda Smith, Colorado State University.

“Some of the most meaningful ecological trends take decades to unfold, and we can only identify them using long-term data such as those supported by the NSF LTER program,” Nippert said. “Without this kind of data, fundamental properties of ecosystems can go undetected with short-term experiments alone.”

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

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

Reference:

1. Zak Ratajczak, Scott L. Collins, John M. Blair, Sally E. Koerner, Allison M. Louthan, Melinda D. Smith, Jeffrey H. Taylor, Jesse B. Nippert. Reintroduction of bison results in a long-lasting and resilient increase in grassland diversity. Proceedings of the National Academy of Sciences, 2022; 119 (36) DOI: 10.1073/pnas.2210433119