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Climate change will likely shift plant and microbial distributions, creating geographic mismatches between plant hosts and essential microbial symbionts (e.g., ectomycorrhizal fungi, EMF). The loss of historical interactions, or the gain of novel associations, can have important consequences for biodiversity, ecosystem processes, and plant migration potential, yet few analyses exist that measure where mycorrhizal symbioses could be lost or gained across landscapes. Here, we examine climate change impacts on tree-EMF codistributions at the continent scale. We built species distribution models for 400 EMF species and 50 tree species, integrating fungal sequencing data from North American forest ecosystems with tree species occurrence records and long-term forest inventory data. Our results show the following: 1) tree and EMF climate suitability to shift toward higher latitudes; 2) climate shifts increase the size of shared tree-EMF habitat overall, but 35% of tree-EMF pairs are at risk of declining habitat overlap; 3) climate mismatches between trees and EMF are projected to be greater at northern vs. southern boundaries; and 4) tree migration lag is correlated with lower richness of climatically suitable EMF partners. This work represents a concentrated effort to quantify the spatial extent and location of tree-EMF climate envelope mismatches. Our findings also support a biotic mechanism partially explaining the failure of northward tree species migrations with climate change: reduced diversity of co-occurring and climate-compatible EMF symbionts at higher latitudes. We highlight the conservation implications for identifying areas where tree and EMF responses to climate change may be highly divergent. 

This article is a Commentary onFernandezet al.,226: 569–582. 

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 About 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 modelled climatic drivers of diversity and community composition with general additive, generalized dissimilarity models and Threshold Indicator Taxa 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 kilometres 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 on ECMF‐associated biogeochemical cycles.