Natural deadwood hosts more diverse pioneering wood-inhabiting fungal communities than restored deadwood

Deadwood can be recreated as a forest restoration measure to increase the amount of deadwood and assist deadwood-dependent biodiversity. While deadwood restoration is known to have an overall positive effect on associated species in the long term, it remains poorly understood how and when wood-inhabiting organisms colonize different kinds of deadwood, which is essential for developing efficient restoration frameworks. In this study, we use DNA metabarcoding to compare wood-inhabiting fungal communities between fresh naturally fallen spruce logs and spruce logs felled for restoration. The results show that although pioneering fungal community composition greatly differs between natural and felled logs, with natural logs hosting more species-rich and heterogeneous communities, felled logs still hold a relatively high fungal diversity. Responses to log type carried a strong phylogenetic signal, and orders Polyporales and Hymenochaetales including most species of conservation concern were more likely to occur in natural than in felled logs. Furthermore, we found that log type was more important for rarely recorded than commonly recorded taxa, suggesting that rare species might be more specialized in their habitat requirements than the common ones. Overall, while restored deadwood can hold a high fungal diversity, the results underline that freshly felled logs do not mimic fresh natural logs. Deadwood restoration should focus not only on increasing the quantity of deadwood but also on the quality of thereof, and most importantly, retaining the existing natural deadwood rather than artificially downing trees.