AIM: Ectomycorrhizal fungi (ECMF) are partners in a globally distributed tree symbiosis implicated in most major ecosystem functions. However, resilience of ECMF to future climates is uncertain. We forecast these changes over the extent of North American Pinaceae forests.

LOCATION: 68 sites from North American Pinaceae forests ranging from Florida to Ontario in the east and southern California to Alaska in the west.

TAXON: Ectomycorrhizal fungi (Asco- and Basidiomycetes).

METHODS: We characterized ECMF communities at each site using molecular methods and modeled climatic drivers of diversity and community composition with general additive, generalized dissimilarity models, and Taxonomic Indicator Threshold Analysis (TITAN). Next, we projected our models across the extent of North American Pinaceae forests and forecast ECMF responses to climate changes in these forests over the next 50 years.

RESULTS: We predict median declines in ECMF species richness as high as 26% in Pinaceae forests throughout a climate zone comprising more than 3.5 million square kilometers of North America (an area twice that of Alaska state). Mitigation of greenhouse gas emissions can reduce these declines, but not prevent them. The existence of multiple diversity optima along climate gradients suggest regionally divergent trajectories for North American ECMF, which is corroborated by corresponding ECMF community thresholds identified in TITAN models. Warming of forests along the boreal-temperate ecotone results in projected ECMF species loss and declines in the relative abundance of long-distance foraging ECMF species, whereas warming of eastern temperate forests has the opposite effect.

MAIN CONCLUSIONS: Our results reveal potentially unavoidable ECMF species-losses over the next 50 years, which is likely to have profound (if yet unclear) effects of ECMF associated biogeochemical cycles.

The file can be accessed in the R statistical computing software and manipulated using the package “phyloseq.” It contains an OTU table, taxonomy information, and sample data from the 68 sites analyzed in our manuscript.