Community structure and dynamics of wood-rotting Basidiomycetes on decomposing conifer trunks in northern Finland

The succession and organization of wood-rotting Basidiomycetes, as indicated by their fruit body production, were studied on naturall y fallen , decomposing trunks of Picea abies (L.) Karsten subsp. obovata (Ledeb.) Domin and Pinus sylvestris L. in northeastern Finland. The study area consists of northern boreal primeval forests that show no signs of forestry practices or wood utilization. Altogether 120 species of Basidiomycetes were found on Picea and 104 on Pinus. The species compositions varied with the following characteristics of the trunks: stage of decay , history of fungal infections preceding the tree fall , diameter and amount of bark. The structures of fungal communities were analysed by using DCA ordination and the divisive clustering technique TWINSPAN. The results indicate that wood-inhabiting fungi succeed each other according to a regular order and that they differ from each other in their association with microclimatic regimes, in their strategies in resource capture, in their competition ability during the wood decomposition, and in their species associates. Physical and chemical properties of the host tree species and the microclimate of the growth site govern the basic trends in the community development of wood-inhabiting fungi. The first steps in tree trunk decomposition greatly depend on the way the tree died. Primary decayers affect the composition of the fungi at later stages of decay , by opening successional path ways for specific groups of saprotrophs. It is concluded that the conser ation of Jignicolous fungi can succeed only after comprehensi ve analysis of fungal community de elopment and the achievement of a thorough understanding of the decomposition dynamics of fallen tree trunks.