This investigation compared the mycofloral populations inhabiting the organic and mineralized soil horizons, and evaluated the effect of castastrophic vegetational disturbances on their species composition, in selected upland forests in northern Wisconsin. Eight forests, part of the conifer—hardwood complex, were included in the study: three of them served as virginal reference stands, four represented secondary succesional communities occupying areas that experienced severe forest fires, and one was a yellow birch forest that became established on a clear—cut area. Sample populations, obtained by the dilution plate method, were isolated from each detectable horizon in each stand. In general, the highly organic large, especially the litter and fermentation horizons, possessed the greatest number of fungal propagules as well as the greatest species diversity. With increasing depth, both the density and diversity decreased rapidly. Although many of the species were present in more than one horizon, most of them exhibited maximum densities and freqencies in only one of them. Thus, the populations colonizing each horizon could be characterized by a somewhat specific combination of prevalent species. The relatively low similarity coefficients derived from comparisons between the populations in the horizons within a stand substantiated the view that there were distinct populations. Ordination of the coefficients suggested that the soil profile could not be visualized as an edaphic cline with elicited a soil microfungal continuum. Since most of the predominant species in any specific horizon differed from those residing in overlying horizons, the establishment of a characteristic mycoflora could not be attributed to differential survival of propagules that percolate from horizons above.