Relationship of Topography to Soils and Vegetation in an Upper Michigan Ecosystem

The influence of topography on soil development and classification and the interrelationships among soils and forest composition are poorly understood in Upper Michigan. Topographic plant-soil interrelations are important because plants are increasingly being used to indicate environmental conditions and potential forest productivity. Our objectives, therefore, were to study the effect of topography on soil development and classification, soil nutrient status, and forest composition over a classical toposequence. An 8-ha portion of a steep watershed was topographically mapped, and soils and plants were sampled and analyzed using established techniques. In addition, the distributions of selected ground flora species were mapped over the landscape. Results indicate a strong correspondence between the distribution of plants, soil development and classification, and soil nutrient status. Soils ranged from a Lithic Dystrochrept in the upper slope through a Typic Dystrochrept, Entic Haplorthod, Dystric Eutrochrept, and finally a Terric Borosaprist in the toeslope; this is considerable variability within a horizontal distance of 300 m. Soil nutrient status varied along with soil development and was strongly related to topographic position. For these coarse-textured soils, increased content of macronutrients is closely associated with increased content of soil organic matter. For example, in the surface soil of a colluvial soil profile we found that soil nitrogen was roughly 10 times greater than in the subsoil; this large difference in soil nitrogen was closely associated with large amounts of soil organic matter in the surface soil. Within the highly variable landscape, forest composition followed variability in soil development, soil organic matter, and soil nutrient status. Groups of ground flora species were closely associated with these soil and topographic variations.