Diversity of fungi in harvested forests 10 years after logging and burning: Polypore assemblages on different woody substrates

The negative biodiversity effects of timber- and biofuel-oriented forestry practices can be alleviated by leaving retention trees and logging residues following clear-cut harvests and occasionally including prescribed bums. Such measures can potentially maintain substrates especially for dead-wood-associated species during young, post-harvest successional stages. However, the availability and temporal patterns of different types of dead wood substrates after cutting are largely unknown, yet these patterns may have a major influence on fungal diversity. We sampled dead wood and the associated polypore fungi - a key wood decomposer group - in a large-scale field experiment with 24 sites, before logging and 2, 4 and 10 years after logging (clear-cut with and without retention trees) and burning. We investigated all old natural dead wood, stumps, slash and retention trees on each site, totaling 98,136 dead wood items. The data include 22,150 records of 122 polypore species collected across all sampling years. Ten years after treatments, we found no differences in the number of species between unlogged and logged or burned and unburned treatment categories, but on the treated sites, the numbers were higher than before treatments. Furthermore, the composition of species assemblages differed as the substrate types available varied between treatments. All dead wood substrate types hosted diverse polypore assemblages. The highest numbers of species were found on slash and retention trees. Furthermore, the polypore assemblages differed between dead wood types. Burning increased the number of species on stumps and red-listed species seemed to increase on burned sites. Our results show that dead wood can host diverse polypore assemblages also in managed forests after timber harvests. However, the pre-requisite for maintaining fungal diversity appears to be that in addition to sufficient amount of substrates - also qualitative variation in dead wood substrates is maintained, including stumps and slash.