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Saprotrophic macrofungi are key decomposers of plant biomass in forests. These fungi form ecologically diverse group where different species specialize in specific substrates. Wildfires produce massive amounts of heterogeneous dead substrates. The postfire succession of saprotrophic fungi on these substrates may have major consequences on how carbon and nutrients are released back to forest ecosystems after a fire.

We studied the effects of a wildfire (covering 143 ha) on saptroptrophic macrofungi (Basidiomycota and Ascomycota) in a Scots pine (Pines sylvestris) dominated forest in eastern Finland during 12 years after the wildfire. In particular, we focused on the consequences that within-fire variation in fire severity had on fungal assemblages. Twenty-two permanent sample plots (10 x 10 m(2) each) were monitored annually. Plots were located on sites with four different fire severity classes and on two unburned control sites. A total of 43 102 sporocarps of macrofungi were collected. Based on fungal life histories, we separated four different groups in the analyses: (1) wood-associated fungi on decayed wood, (2) decomposers of organic matter in soil or that live on bare mineral soil in forest floor, (3) biotrophic macrofungi that are associations between algae and fungi and that may also be symbiotic with mycorrhizae fungi, and (4) parasites on a living host plant or other fungi.

In total, 219 species were observed. Fire severity affected species richness and composition, and fire always increased fungal diversity in comparison with unburned control sites. On the burned sites, species richness was highest on sites of medium burn severity (114 species in total, vs. 88-106 spp. on other burned sites). Substrate association of species was closely connected to assemblage dynamics: on soil and humus substrates, the succession of fire-associated pyrophilous species was rapid when compared to the succession of aphyllophoroid wood-associated macrofungi (AWAM). Pyrophilous and AWAM assemblages comprised many indicator species that occurred only ephemerally during the few years after the fire.

In previous studies, AWAM assemblages often respond negatively to forest fires in short-term. Our results, however, show that if also other than AWAM macrofungi are included, there are several species typical for immediate post-fire habitats. The role that these species have on forest ecosystem and for example on carbon dynamics after a wildfire remains an important topic for future studies. From the conservation viewpoint, the finding emphasizes that post-fire young successional forests are important habitats for specialized and rare fungi.