Spatial and physical characteristics of bison wallows in the Flint Hills of Kansas

Abstract Bison have long been considered a keystone species of North American prairies, increasing plant and animal diversity through a number of unique behaviors. One such behavior is wallowing, in which the repeated rolling of bison in the same spot leads to the formation of small, shallow, oval depressions called wallows. The objective of this study was to characterize spatial and physical attributes of bison wallows at the Konza Prairie Biological Station, a tallgrass prairie preserve in northeastern Kansas. We used aerial imagery from two different years (2011 and 2019) to assess the abundance and spatial distribution of these wallows in relation to fire frequency, elevation, and slope. We also recorded physical characteristics (2020) for a randomly selected subset of wallows and analyzed these data in relation to the same landscape features. Results from the analysis of the aerial images indicated that wallows were more abundant in areas characterized by combinations of more frequent burning, higher elevations, and little or no slope. In the 2020 physical measurements, we found that wallows were smaller in areas burned more often and shallower at higher elevations, particularly when located on grazing lawns. Terrestrial plants were found in approximately 72.1% of the wallows that were physically sampled, and their prevalence increased with increasing slope. We found some quantity of aquatic plants in approximately 7.1% of the sampled wallows. The probability of finding aquatic vegetation in wallows was higher on grazing lawns and in areas burned less frequently, particularly every 20 years. This study enhances the understanding of the distribution of wallows and their physical characteristics as a type of disturbance that could alter relationships within grassland communities.