Fallen retention aspen trees on clear-cuts can be important habitats for red-listed polypores: a case study in Finland

Green-tree retention is a relatively new forestry application, which aims at decreasing the negative effects of clear-cut logging on forest biodiversity. In this study, the value of retained aspens in maintaining diverse assemblages of wood-decaying fungi (polypores; Basidiomycota) on clear-cuts was investigated, after the retention trees had died, fallen and started to decay. A total of 110 fallen aspen trunks were investigated on clear-cuts and within old-growth forests in eastern Finland, southern boreal zone; and 499 records of polypores belonging to 46 species were made. The intermediately decayed trunks on a clear-cut area hosted more species and more red-listed species than did trunks within forests. Most of the polypore species with more than two records were found in both habitats. These results suggest that many aspen-associated polypores are able to live and reproduce in sun-exposed habitats, if the quality and quantity of dead wood fulfill the species-specific requirements. This unexpected result, however, may be partly due to the exceptionally great abundance of aspen in the study area. Furthermore, in the long term, the local benefits of fallen retention trees can be limited, unless the local continuity of large aspens, both living and dead, is ensured.