The structure of macrofungal assemblages in boreal forests, with particular reference to the effect of fire on Basidiomycota and Ascomycota

Abstract

The majority of forests in Finland have been subject to intensive clear-cutting and thinning, and peatlands have been extensively ditched and fertilized. Such changes have modified forest environments but the effects of these changes on macrofungi are still unclear. This thesis examines macrofungal communities in boreal forests and peatlands, with particular focus on the effects of wildfire, prescribed burning and tree retention (timber harvest intensity) on ectomycorrhizal (ECM) and saprotrophic (SM) macrofungi (Basidiomycota and Ascomycota). The thesis is based on empirical field data, which includes over 550 species and a monitoring period of up to 12 years. Fertile forests had more diverse ECM and SM assemblages than the dry and semi-dry forests. Non-ditched pine bogs had less macrofungi than drained spruce mires, pine mires and pine bogs. Rare and Red-listed agarics and aphyllophoroid wood-associated macrofungal species were rare in managed forests. In general, wildfire increased the richness and sporocarp production of several SM species and also modified assemblage composition. ECM diversity was greatest in the mild and intermediate fire sites where it was three-fold higher than the high-severity fire sites. The succession of fire-associated pyrophilous species in burned humus was rapid. Prescribed burning and harvest intensity had a major influence on macrofungal populations. However, these effects were strongly dependent on the functional group. Clear-cut areas had an overall adverse effect on macrofungi; ECM species in particular disappeared after clear-cutting. Several SM species occurred exclusively on burned areas, and retention areas had a slight positive effect on macrofungi, including ECM species. My results show that macrofungal assemblages are diverse and vary systematically in forest and peatland site types. Intensive forest management has mostly negative effects on macrofungi, including edible mushroom species. Prescribed fire in the forest landscape and a reduction in harvest intensity can be used to maintain fungal assemblage diversity in managed forests.