09/24/2026
Destruction caused by buffalo creates biodiversity, making it construction. The non-grazing behavior of wild, migratory buffalo is as important to the prairie as their grazing is.
A bison rolls in dirt to scratch an itch, shed winter fur, and drive off biting insects. The depression it leaves behind can last for decades, fill with rainwater, grow plants the surrounding prairie does not support, and function as a miniature wetland long after the bison that made it is dead. A dust bath that outlives the animal becomes an ecosystem.
Bison wallows are shallow depressions, typically 10 to 15 feet across and up to two feet deep, formed when bison repeatedly roll in the same spot. The rolling strips vegetation, compacts the soil, and creates a basin that holds water after a rainstorm when the surrounding grassland drains. A single wallow used by generations of bison deepens and hardens over years until it functions as a natural catchment in a landscape where standing water is scarce for most of the year.
Researchers at Konza Prairie Biological Station in Kansas, the longest-running tallgrass prairie research site in North America, have identified over 50 plant species that grow specifically in and around bison wallows but rarely establish elsewhere on the prairie. The disturbed soil, the retained moisture, and the absence of the dense root mat that dominates undisturbed grassland create conditions that flowering forbs and pioneering species need to germinate. A recent Seedbank study spanning sites in South Dakota found wallows support a higher proportion of medicinal and aromatic plants than surrounding grassland, including species historically used by Indigenous communities.
The wallows also function as breeding habitat for animals that need temporary water. Tiger salamanders and chorus frogs use flooded wallows as egg-laying sites in spring. Shorebirds and waterfowl visit during migration. Aquatic invertebrates colonize the standing water within days of a heavy rain. A bison wallow after a thunderstorm is a vernal pool on a prairie that otherwise has none.
Nickell and colleagues published the arthropod data in Ecosphere in 2018. They compared insect communities on active wallows, abandoned wallows, and undisturbed prairie at the same sites. Active wallows, still being used and regularly stripped bare by rolling bison, held fewer arthropods than the surrounding grass. Abandoned wallows held more. Higher abundance. Higher species richness across several feeding groups. The destruction the bison caused while alive created conditions that increased biodiversity after the bison moved on. The researchers described bison as ecosystem engineers whose non-feeding behaviors, wallowing specifically, are potentially as important to prairie biodiversity as their grazing.
That engineering disappeared when the bison did. Before European settlement, an estimated 30 to 60 million bison maintained millions of wallows across the Great Plains. The wallows were so numerous and so persistent that early settlers used them as landmarks and watering points. When the herds were shot to near extinction in the 1870s and 1880s, the wallowing stopped. The depressions filled in. The plant communities they supported lost their substrate. The ephemeral wetlands they created dried up. Cattle replaced bison on most of the remaining grassland, but cattle do not wallow. They graze the same grass but they do not roll in the same dirt, which means they do not build the depressions that hold the water that grows the plants that feed the insects that the prairie evolved with.
Image is for illustration purposes only
Source: Nickell, Varriano, Plemmons, and Moran (2018), Ecosphere / Konza Prairie Biological Station / WWF Seedbank Study / McMillan et al. (2011) / Uno (1989) / Polley and Wallace (1986) / Wikipedia, Buffalo Wallow.
