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Description

Abstract

Ectomycorrhizal fungi (EMF) are sensitive to stand-removing disturbances. The re-establishment of diverse EMF communities, including return of the rarer fungi typical of old-growth stands, may take longer than a century. Using smaller cutovers, with their high edge to area ratio, has the potential to accelerate postharvest EMF community recovery by increasing proximity to mature forests. By contrast, forest edges produce a fragmentation effect that could eventually inflict a negative influence on EMF taxa of the remaining forest.

We compared both succession and fragmentation patterns across small openings at 27 years postharvest in a high-elevation coniferous forest. We sampled 90 m transects across forest edges of nine 1-ha 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 significant differences among species assemblages between the opening, edge and interior forest habitats. Furthermore, EMF richness of root tips in the openings declined by 27%, on average, beginning at 10 m from the forest edge, illustrating how the previously observed influence of overstory trees had not expanded into the openings during this time. An influx of multi-seral taxa into the young stands was instead likely driven by spore dispersal, which may have been facilitated in these small cutovers where regenerating saplings were never more than 50 m from mature trees. While EMF richness on tree roots was maintained in the interior forest, sporocarp fruiting was curtailed within forest edges, alongside some reductions in forest- dependent taxa, likely reflecting fragmentation stress.

Overall, the potential benefits of small openings appeared constrained by environmental factors, such as open canopies and limited rooting density, that delay the re-establishment of late-seral EMF species. The negative effect of edges on EMF reproduction and abundance of some taxa in the forest adjacent to the openings should be considered when designing retention forestry systems as part of sustainable forest management. Our results suggest medium to large patches of retained trees may reduce fragmentation stress and better sustain an array of late-seral forest fungi.

We sampled 90 m transects across forest edges of nine 1-ha openings, using Pacific Bioscience (PacBio) sequencing of EMF from mycorrhizal root tips, and Sanger sequencing of epigeous sporocarps to assess EMF community response. PacBio sequences were analyzed using DADA2 and fungal names were assigned using a combination version 8 of the full UNITE + INSD dataset for eukaryotes and a priori knowledge.