In order to assess changes in the community structure of ectomycorrhizal fungi across the tree line, data on distributions of fungi and their host plants, as well as on edaphic factors and stand age, were collected at two montane sites in the Front Range of the Canadian Rockies. Canonical correspondence analysis (CCA) was used to explore relationships between fungal species composition and environmental factors. Richness and diversity of ectomycorrhizal fungi decreased with elevation, in spite of the fact that host plant diversity was highest at the ecotone between the subalpine forest and the alpine zone. Both host plant distribution and edaphic factors were important in explaining the observed changes in fungal species diversity and composition. The majority of ectomycorrhizal fungi found in the subalpine forest and at the ecotone were conifer associates, while a large proportion of those in the alpine zone were non-host specific and able to form mycorrhizae with both angiosperms and gymnosperms. The abundance of non-host specific fungi in the alpine zone is expected to provide a favorable environment for the establishment of conifer seedlings above the present tree line.