Exploring Confusing Soil and Ecological Relationships of the Des Moines Lobe in Minnesota and Iowa, USA

by

Kyle Steele, Clayton Johnson, Danielle Evans, and Greg Nowacki

USDA Natural Resources Conservation Service, Soil Science Division, 1400 West Main Street, Albert Lea, MN 56007

Abstract – The Des Moines Lobe of the Wisconsin Glaciation is an expansive and agriculturally important ecoregion consisting of nearly 18 million acres. Predominate soils of the region are classified as typical Mollisols developed under tallgrass prairie vegetation, which is characteristic of the semi-arid environments of the central and northern Great Plains. Still, we estimate at least 2.5 million acres contain soils developed under various treed conditions, ranging from open savannas to closed forests. The majority of these areas were mapped as various transitional soils, having properties of both prairie and forest soils (e.g., dark surfaces, leached horizons, clay-enriched horizons, etc.). Many populations of these soils occur in isolated pockets within the central portion of the Des Moines Lobe, often on the leeward side of fire breaks, such as lakes, stream valleys, or comparatively rough terrain. Based on bearing tree analysis, these areas were primarily oak savanna. In contrast, the majority of these soils are located in the northeastern portion of the region where mesic hardwood forests were the dominant vegetation type (colloquially referred to as “Big Woods” forests). Here, transition to forest soils from the south and west is rather abrupt, where Mollisols (i.e., Typic Hapludolls) apparently abut Alfisols (i.e., Mollic Hapludalfs). Currently, the same soil map units are associated to each of these ecologically contrasting conditions. With interest mounting related to the development of USDA Ecological Site Descriptions, we explore these soil-ecosystem interactions and recommend potential areas for improvement to soil maps.