NSF Award
2324988
Multi-year extreme droughts have greatly impacted grasslands of the Great Plains in the past and will likely become more common. Before the last big drought in the Great Plains -- the “Dust Bowl” -- humans had essentially removed bison and other large animals by hunting. Therefore, the influence of these once widespread animals during extreme drought is unknown. Yet scientists know that in normal times, large grazers such as bison drastically alter grasslands’ soil and plant life. For example, one long-term study found that reintroduction of bison increases the abundance of plant species adapted to drought and grazing. Since the Dust Bowl, bison have been reintroduced to relatively small areas of grassland throughout the Great Plains. To prepare for future changes in climate, scientists need experiments that measure how bison and other large grazers shape grasslands’ response to extreme droughts. For instance, can grazed tallgrass prairie provide quality forage after several years of drought? Will the plant biodiversity that supports pollinators be resilient or decline? Such questions remain unanswered because the experimental design used to simulate droughts -- large shelters that divert rain away from plants underneath -- is untested in places where bison have been reintroduced. In particular, bison may avoid, congregate under, or destroy such “rainout” shelters, in which case experiments that rely on them would be unable to test what they were supposed to test. This study will assess the effectiveness of multiple types of rainout shelters and whether a) bison use areas under rainout shelters at similar rates as areas not under rainout shelters, b) bison destroy or damage rainout shelters, and c) whether rainout shelters block enough rainfall to simulate extreme drought. Results will inform future experimental designs and help rangeland managers determine best practices for grazing under increasingly arid conditions.<br/><br/>Both drought and grazers strongly influence grassland systems, and a large body of work has quantified the response of grasslands to each of these drivers separately. But drought and grazing may interact to influence grassland form and function. For example, grazed plant communities often have different species composition than ungrazed communities, and those species could be more (or less) sensitive to drought. Grazed plants could also have a reduced ability to respond to the additional stressor of extreme drought. Our understanding of such interacting effects is limited because of the logistical challenges associated with manipulating drought in the presence of large grazers. This project will experimentally manipulate drought in the presence and absence of large grazers, using a variety of experimental designs. The goal is to test the feasibility of independently manipulating drought and grazing on communities of prairie plants. Specifically, researchers will develop methodologies to establish experimental drought manipulations in the presence of a key large grazer in the Great Plains, bison, at Konza Prairie Biological Station and Long-Term Ecological Research Site. Researchers will establish rainout shelters and quantify bison use and activity levels under the shelters. They will conduct an iterative method of shelter designs, testing one design first and then modifying as necessary to elicit the intended responses (namely, similar levels of bison use under and away from the shelters and a 50% reduction in soil moisture under the shelters). Results will provide pilot data essential for designing a much larger experiment on the interaction of drought and grazing on plant communities. The long-term objective is to understand how these two fundamental drivers influence grassland populations, communities, and ecosystems.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
