Conservation of polypore diversity in managed forests of boreal Fennoscandia

Abstract

In this thesis patterns of polypore assemblages are described along the gradients of forest succession and naturalness, and the effectiveness of some biodiversity-oriented forestry methods for maintaining the diversity of polypores in managed forests is evaluated. The thesis is based on four different data sets collected in eastern Finland 1996-2005. The data include a total of 19 617 records of fungi (based on presence of fruiting bodies) representing 129 species of polypores and 133 species of corticiaceous fungi. The main findings of the thesis are as follows: 1) For wood-inhabiting fungi, in managed as well as in natural forests, the most speciesrich phase of forest succession is the first stage after a major disturbance (wildfire or clearcutting). The fungal assemblages at the first stage of forest succession are distinctive, particularly in natural forests, compared to the assemblages at later successional stages. 2) After the first stage of succession, the level of forest naturalness is more important than the successional stage in determining the diversity of polypores. Particularly threatened species suffer with increasing levels of management intensity, and in the most intensively managed forests, no threatened species can be found. 3) Fallen retention aspens can be suitable habitats for several polypore species, including many red-listed species. 4) Woodland key habitats, as defined in the Finnish Forest Act, can support several polypore species, but provide little help for red-listed species. 5) The short-term effects on polypores from logging are more dramatic than the effects of fire. On the time scale of four years, logging changes the species composition of polypore assemblages, increases dominance and increases the overall polypore abundance, but decreases the proportion of red-listed and species designated as biodiversity indicators. The results presented in this thesis underline the fundamental importance of dead wood, its amount and diversity, in maintenance of species diversity in managed forests. Of the current biodiversity-oriented forestry practices, tree retention (at clear-cut sites) can be an effective way of supporting polypore diversity, including red-listed species. However, current retention levels need to be increased to support diversity. The short-term value of “woodland key habitats” and prescribed burning seem to be limited with regards to polypores. The long-term effects, however, may prove to be different. Measures enhancing the diversity of polypores are also likely to improve the living conditions of other taxa dependent on dead trees or large living trees, thus supporting the maintenance of the most threatened part of species diversity in the Fennoscandian boreal forests.