Arbuscular mycorrhizae fungi (AMF) occur in most terrestrial ecosystems and are crucial to plant community structure and function. This study examined the distribution of AMF propagules, spores, and colonized plants across the Pumice Plain of Mount St. Helens 23 years after its eruption, documenting the changes since 1993. Propagules of AMF were detected by using the mycorrhizal inoculum potential assay in six microsite types across the Pumice Plain. Fifteen species of AMF were isolated from spore trap cultures, and spores were found in all of the microsites, although the distribution was aggregated. The vegetation of the Pumice Plain is currently composed primarily of facultatively mycotrophic species, which are predominantly associated with arbuscular mycorrhizae. Mycorrhizal colonization and propagule levels continue to increase as primary succession proceeds.
