Mia R. Maltz ^1* Michael F. Allen ² Michala Phillips ² H L. Freund ² Rebecca R. Hernandez ³ Hannah Shulman ⁴ Lela V. Andrews ⁵ Jon Botthoff ² Emma L. Aronson ²

• ¹ University of Connecticut, Storrs, Connecticut, United States
• ² University of California, Riverside, Riverside, California, United States
• ³ University of California, Davis, Davis, California, United States
• ⁴ The University of Tennessee, Knoxville, Knoxville, Tennessee, United States
• ⁵ Tecan Genomics, Redwood City, United States

The type and abundance of biotic propagules and legacies in recovering ecosystems are important variables for determining post-disturbance successional trajectories. Soil microorganisms regulate nutrient cycling, interact with many other organisms, and therefore may support successional pathways and complementary ecosystem functions, even in harsh conditions. The 1980 eruption of Mount St. Helens had devastating effects above and belowground in forested montane ecosystems, including the burial and destruction of soil microbes. Historic forest management methods, such as old-growth and clearcut regimes, and locations of small mammal enclosures, may have influenced microbiome resilience in response to this catastrophic eruption. Our study compared the microbes in Volcanic eruption and microbiome rescue old-growth and clearcut forests, as well as in locations of historic short-term gopher enclosures (Thomomys talpoides), to evaluate community response to forest management practices and to examine vectors for dispersing microbial consortia to the surface of the Pumice Plain. These biotic interactions may have primed ecological succession in Bear Meadow and the Pumice Plain by creating microsite conditions conducive to primary succession and plant establishment. Using molecular techniques, we examined bacterial, fungal, and AMF communities to determine how these variables affected microbial communities and soil properties. We found that bacterial/archaeal 16S, fungal ITS2, and AMF SSU community composition varied among forestry practices and among sites with long-term lupine plots and gopher enclosures. The findings also related to detected differences in C and N concentrations and ratios in soil from our study sites. These data suggest that the fungal communities from previously clearcut locations were less diverse than in gopher plots within the Pumice Plain. These clearcut meadows also harbor fewer ancestral AM fungal taxa than were found within the old-growth forest. By investigating both forestry practices and mammals in microbial dispersal, we evaluated how these interactions may have promoted revegetation and ecological succession within the Pumice Plains of Mount St. Helens. In addition to providing evidence about how dispersal vectors and forest structure influence post-eruption soil microbiomes, this project also informs research and management communities about belowground processes and microbial functional traits in facilitating succession and ecosystem function.