Macrofungi on fallen oak trunks in the Białowieża Virgin Forest – ecological role of trunk parameters and surrounding vegetation.

All groups of macrofungi were recorded on 32 large fallen trunks of pedunculate oak ( Quercus robur ) in various decay stages in the strictly protected zone of Białowieża National Park, Poland. The total number of species was 187 with 4–38 species per trunk. The mycobiota of individual trunks was unique, consisting of a variable set of several frequent species, a high number of infrequent to rare ones, and a considerable proportion of mycorrhizal fungi and species preferring conifer wood. Relations between trunk parameters, surrounding vegetation and fungal occurrences were analysed using multivariate statistical methods. The number of fungal species per trunk was significantly correlated with trunk orientation, which reflects the heat load via forest canopy gap, trunk size parameters, percentage of bark cover and contact with the soil. The species-richest trunks were those covered by bark, of larger volume (thick, long), not exposed to heat from afternoon sun, but, simultaneously, with lower canopy cover. Orientation (azimuth) of the fallen trunks proved to be significant also for the fungal species composition of a particular trunk, which also reflected trunk size characteristics, its moss/bark cover and contact with the soil. Presence of some dominants ( Ganoderma applanatum , Mycena inclinata , Kretzschmaria deusta , Xylobolus frustulatus ) had a significant effect on fungal community composition. Some herbs requiring nutrient-rich soils occurred in the vicinity of trunks with a larger contact area with the soil and in later stages of decay. The process of oak trunk decay in relation to fungi and surrounding vegetation is outlined.