Detailed analysis of fungal communities in Norway spruce logs reveals stochastic fine-scale patterns of species and detects lichen forming fungi without their photobionts

Fungal ecologists have long been intrigued by the mechanisms behind the high fungal species richness in dead wood at small and large spatial scales. We identified processes resulting in fine-scale fungal community patterns with a network analysis based on a detailed metabarcode mapping of fungi in and on the surfaces of eight naturally fallen Norway spruce logs in northern Sweden. Our results show that (1) dominant species and communities of fungi vary significantly among the logs, (2) wood inside and on log surfaces has distinct and diverse fungal compositions and (3) consistent co-occurrences of fungi in wood are rare. These patterns suggest priority effects favouring primary colonizing species are important for determining which becomes the dominant species, and that colonization of the rest of the community and fungal co-occurrences are largely shaped by stochastic processes. Furthermore, lichen-forming fungi were detected without their photobionts in wood, indicating possible free-living stages.