Ectomycorrhizal fungal community succession and fragmentation across forest edges nearly three decades postharvest

Societal Impact Statement Forest management for wood products involves the conversion of primary forests to younger plantations. This has an immediate impact on biota such as ectomycorrhizal fungi, a diverse symbiotic fungal community. Alternatives to large clearcuts may be one way to mitigate harvesting effects. We tested this premise by examining ectomycorrhizal fungal communities across forest edges in 1‐ha openings at nearly three decades postharvest. We found reductions in species richness and shifts in community composition were still evident, illustrating how recovery was limited by the open canopies of younger trees. Sustainable management of ectomycorrhiza may require further conservation strategies, particularly green‐tree retention. Summary Ectomycorrhizal fungi (EMF) are sensitive to stand‐removing disturbances; diverse EMF communities, especially rarer fungi typical of old‐growth stands, may take a century to re‐establish. Proximity to mature forests via small cutovers could accelerate postharvest EMF community recovery, thereby supporting sustainable forest management. Alternatively, forest edges may impose a fragmentation effect, which could eventually negatively influence EMF taxa in the remaining forest. We compared both succession and fragmentation patterns across 1‐ha openings 27 years postharvest in a high‐elevation coniferous forest. We sampled 90‐m transects across forest edges of nine openings, using long‐read metabarcoding of EMF from mycorrhizal root tips, and Sanger sequencing of epigeous sporocarps to assess EMF community response. A timber harvesting effect on root tip EMF communities was still evident, with differences among species assemblages between the opening, edge zone, and interior forest habitats. EMF richness of root tips in openings declined by 27%, on average, beginning at 10 m from the forest edge. While EMF richness on roots was consistent across forest plots, fruiting was curtailed within forest edge zones, alongside some reductions in forest‐dependent taxa. Overall, the potential benefits of small openings were apparently constrained by environmental factors that delay the re‐establishment of late‐seral EMF species under open canopies. The negative effect of edges on EMF reproduction and some taxa abundance in the forest adjacent to openings is relevant when designing green‐tree retention forestry systems, suggesting medium to large patches of trees may reduce fragmentation stress and better sustain an array of late‐seral fungi.