Fungi associated with Engelmann spruce and subalpine fir were studied in a high altitude area of western Wyoming. Thirty permanent plots were established and their mean stand age determined. Three age classes were delineated: young (78 years), mature (127 years), and old-age (216 years). Stand and soil parameters including density, basal area, and soil pH, P, K, Ca, organic matter, and Mg concentrations were used to define similarities in stand characteristics. Sporocarps of higher basidiomycetes and ascomycetes were collected and identified, and ectomycorrhizal root tips sampled from each plot. Pure cultures of the basidiomycetes were routinely attempted. Mycorrhizal syntheses were subsequently attempted with both tree species using successful pure cultures. Thirty-nine species of higher fungi were collected during the study. Distribution of sporocarps throughout the age classes revealed a distinct fungal flora in each age class. Greatest density of species appeared in the mature stands. Non-mycorrhizal fungi were more abundant in the mature stand while mycorrhizal species were more abundant in the old-age stand. Mycorrhizal root counts increased from young to old-age stands. Low numbers of sporocarps and mycorrhizal rootlets were collected from the young stand. It seems evident from this study that a more diverse assemblage of higher fungi is present in mature and old-age forests and a progressive increase of fungal species from young to old-age stands supports the hypothesis that fungal succession is occurring in the study area. / Master of Science