Fungal diversity and potential tree pathogens in decaying logs and stumps

• Fungal composition differs between stumps and logs of the same tree species.
• Different potential fungal tree pathogens were found in logs and stumps.
• Fungal diversity increases when different wood sources are combined.
• Different wood sources may increase the risk of survival of tree pathogens.

Different types of dead wood in forest ecosystems contribute to an increase of habitats for decomposer fungi. This may have a positive effect on fungal diversity but may also increase habitats for tree pathogens. In this study we investigate the fungal diversity and composition via high-throughput sequencing in decaying stumps and logs (three years after cutting) of two tree species (Larix kaempferi and Quercus rubra) in a forest site.Fungal diversity and composition in decaying wood was different between tree species, between stumps and logs of the same tree species, and between sapwood and heartwood. When different wood sources were combined, fungal species diversity increased. This indicates that different wood sources contribute to fungal diversity and, therefore, species conservation in forests.Potential fungal tree pathogens were found in L. kaempferi stumps and logs, whereas their occurrence was generally less in Q. rubra wood sources. No clear difference was found in the relative abundance of potential fungal tree pathogens between stumps and logs, but some potential tree pathogens were only found in either stumps or logs. This indicates that both logs and stumps can be habitats for potential fungal tree pathogens, and each wood type seems to harbor different fungal tree pathogens.In conclusion, forest management practices that aim at maintaining different types of dead wood seem to positively affect fungal diversity, but may additionally increase the risk of survival of potential tree pathogens. This potential risk seems to depend on the tree species.