The interaction of elevated soil temperature, ash deposition and biotic factors associated with untreated subsurface soils on the patterns of sporocarp appearance among populations of carbonicolous ascomycetes in a prairie soil was studied in the laboratory. Ash or unheated prairie soil, when separately combined with aerated steam-heated soil, disrupts the biotic associations, affecting both the production of sporocarps and their order of appearance. With either of these treatments, the interval required for sporocarp appearance among several species was extended but never abbreviated. When ash and a subsurface layer of unheated soil were applied together to create a "simulated burn," the successional pattern was similar to that observed in soil samples collected immediately following prairie burning. The biological causes of this disturbance-mediated heterotrophic succession include: (1) the growth rate and minimal time required for sporulation among individual species populations, and (2) an overall pattern of competitive hierarchy. We suggest that the order of appearance of ascomycetes on recently-burned soils may be the evolutionary outcome of interspecific competition.