LAWRENCE — Reintroducing bison to tallgrass prairies can double biodiversity of native plants and increase drought resistance, a Kansas State University study found.
The study collected 29 years of data from the Flint Hills.
Native species biodiversity increased between 0.58 and 1.06 species per year, depending on the area with the introduction of bison. Researchers found that introducing cattle increases biodiversity by half, as compared to bison. Dominant grass cover in areas where bison grazed was significantly lower than in ungrazed areas but the grass was not eliminated completely.
The area bison grazed was cleared and gave space for new native plants to thrive. This finding was replicated by cattle, but to a lesser extent. Researchers credit this to differences in their grazing habits.
Bison are year-round grazers, whereas cattle typically only graze during growing seasons. Bison also form grazing lawns, whereas cattle do not. Grazing lawns create areas that lead to a significant decline of dominant grasses, which help create a concentrated area for diverse species to grow.
RESEARCHERS gathered data on the species from the 2011 and 2012 droughts, which researchers say were one of the “most extreme drought events that have occurred in the Great Plains since the 1930s Dust Bowl,” and found that the new biodiverse species were resilient during droughts.
“The resilience we found in the bison grasslands is also consistent with the idea that diversity promotes ecological resilience,” said researcher Zac Ratajczak. “And this resilience will only become more important if our climate becomes more extreme.”
Recovery in the bison-grazed areas was rapid, and rebounded to pre-drought levels within two to four years. Researchers found lower resilience in cattle-grazed areas than bison-grazed areas, but it remained higher than ungrazed areas. This is because the dominant grasses in ungrazed areas rely heavily on shallow soil water, and the biodiverse species often rely on deeper soil water. The increase in competition for water between grasses decreases their resilience and ability to rebound.
Researchers predict there used to be millions of bison in the Great Plains, but pioneer settlements drove them to near extinction by the late 1800s. Today, there are about 5,000 bison in Kansas. Ratajczak said the removal of bison occurred before quantitative records, meaning the full effects of their removal are unknown.
“Our results suggest that many grasslands in the central Great Plains have substantially lower plant biodiversity than would have occurred before bison were widely wiped out,” Ratajczak said. “Returning or ‘rewilding’ native megafauna could help to restore grassland biodiversity.”
