THE DISTRIBUTION OF SPODOSOL SOILS IN SOUTHERN MICHIGAN - A CLIMATIC INTERPRETATION

This study describes and explains the geographic distribution of Spodosol soils (Podzols) on a regional scale. We employ a spatially-based, functional-factorial model of soil formation and, by holding four factors constant, are able to examine the effects of climate on soil genesis and distribution. Analysis of soils data for the southern peninsula of Michigan reveals that well and moderately well-drained, sandy Spodosols are found primarily in the northern half of the region in association with mixed coniferous-deciduous forest. Within this "Spodosol province," degree of soil development varies markedly. Differences in degree of soil development among sandy sites appear to be independent of present-day (or presettlement), regional vegetation patterns and may be related to variations in climate. Infiltration and "soil freezing potential," calculated using a hydrologic model, as well as air temperature records, are analyzed to ascertain which climate factors best correspond to observed trends in Spodosol development. Soils with strong spodic development exist in areas of northwestern southern (lower) Michigan that commonly experience deep lake-effect snows. Deep snowpacks in early winter inhibit soil frost, allowing for unrestricted infiltration of meltwater into the mineral soil during the spring snowmelt period (March and April). Correspondence between areas of increased autumn infiltration and strong Spodosol development suggests that wet soil conditions at the onset of winter also have impact on soil development, probably by inhibiting soil frost. Whereas the overall distribution of Spodosols is related to a coniferous component in the forest, variation in the degree of Spodosol development appears to be related to the frequency of years with high amounts of snowmelt infiltration, which intensifies the podzolization process.