Megagrazer rewilding results in long-running and resilient biodiversity gains in a Great Plains grassland

Zak Ratajczak, John Blair and Jesse B. Nippert, Division of Biology, Kansas State University, Manhattan, KS, Scott Collins, Department of Biology, University of New Mexico, Albuquerque, NM, Sally E. Koerner, Department of Biology, University of North Carolina Greensboro, Greensboro, NC, Allison Louthan, Environmental Studies, University of Colorado- Boulder, Boulder, CO, Jeffrey Taylor, Konza Prairie LTER, Manhattan, KS, Melinda Smith, Department of Biology, Colorado State University, Fort Collins, CO

Background/Question/Methods
The widespread extirpation of megafauna has destabilized ecosystems and altered biodiversity globally. Across many grasslands, native megagrazers are either absent or have been replaced by domesticated megafauna—usually domestic cattle (Bos tauras). In North America, most extirpations of native megafauna occurred before the modern record, leaving it unclear how much modern-day biodiversity reflects their loss. Here we report on a long-term (30 years) reintroduction of a native megaherbivore, Plains Bison (Bos bison) and cattle (Bos taurus), to native tallgrass prairie. Plant community responses were measured in areas grazed by each herbivore and in ungrazed prairie using a network of long-term, permanently located 10 m2 plots per treatment (n=80). An extreme drought and heatwave occurred in year 21 and 22 of the reintroduction, which allowed us to contrast resilience to climate extremes in the presence/absence of megagrazer reintroduction.
Results/Conclusions
Following bison reintroduction, plant species richness and diversity increased relative to ungrazed controls. These biodiversity gains are multi-scalar, with a doubling of average species richness at finer scales and a 65% increase at the landscape scale. Gains in diversity have occurred for >30 years exhibiting high resilience to extreme drought and heat waves. Domestic grazers (cattle, B. taurus) also increased diversity and those gains were also resilient to the climate extreme. However, cattle have produced only half as much biodiversity gains as bison. We conclude that (1) some ecosystems maintain a latent ability to increase native plant diversity following reintroduction of native herbivores and (2) that these gains are potentially resilient to climate extremes that will become more common in the future under global environmental change. These gains are apparent across several scales, ranging from the size of smaller (<1 km2) to larger land holdings (>4 km2).