Grassland Soil Depressions: Relict Bison Wallows or Inherent Landscape Heterogeneity?

Abstract

Abstract Wallows are circular soil depressions created by repeated bison (Bison bison L.) dust-bathing. Despite more than a century of bison absence from the Great Plains and lack of evidence on wallow persistence, many studies have classified grassland soil depressions as ‘relict’ wallows. We studied bison wallowing on a tallgrass prairie site in Oklahoma where bison were reestablished in late 1993. Bison use of existing soil depressions fitting descriptions for relict wallows located before reintroduction and bison formation of new active wallows were documented from 1993–1995. Bison avoided existing depressions, instead forming active wallows in different locations. Bulk density and soluble salt, sodium and clay content of soils in existing depressions were significantly higher than soils in active wallows or nearby reference sites. These depressions occurred primarily on shale-derived soils rich in silt and clay, whereas active wallows were formed mostly on sandy loam soils overlying sandstone. The sp...