ABUNDANCE, VEGETATION, AND ENVIRONMENT OF 4 PATCH TYPES IN A NORTHERN MIXED PRAIRIE

The importance of concurrent disturbances to the maintenance of plant species diversity in grasslands has been emphasized by several authors, but there are few studies comparing different disturbances at the same site. In this study the size, abundance, vegetation, and environment of thatching ant mounds, earthen mammal mounds, bison wallows, and openings in dry marshes are compared in a northern mixed prairie in north central South Dakota. Patch size and abundance varied considerably between patch types. Ant and earthen mammal mounds were the smallest but most abundant patch types. Bison wallows and dry marshes were larger and occurred less frequently than ant and earthen mounds. Different patch types occupied a similar amount of area. Ordination of patch vegetation revealed marked between-type compositional differences; ant and earthen mounds were dominated by vegetatively reproducing perennials, while annuals occurred more abundantly in bison wallows and dry marshes. Many species were restricted to either wallows or marshes. Levels of nitrate, phosphorus, soil organic matter, and other environmental factors varied significantly between patch types. Different patch types supported different groups of species, and patch vegetation was a product of mechanism of patch creation, patch environment, and location.