Macrofungi on large decaying spruce trunks in a Central European old-growth forest: what factors affect their species richness and composition?

Species richness and composition of macrofungi on huge fallen trunks of spruce (Picea abies) were monitored at a model old-growth forest locality, Boubinsky prales virgin forest (Czech Republic). Using detailed survey of all macrofungal groups based on fruit bodies, 168 species were recorded on 33 trunks with a diameter of 100-150 cm, which is a very high species richness. Individual trunks were inhabited by 6-32 species. The number of species per trunk was positively correlated with increasing tree cover, medium decay stages, and decreasing altitude. The species-richest groups were resupinate fungi with annual basidiomata and fleshy saprotrophic fungi. Species composition on particular trunks was significantly influenced by percentage of bark cover, altitude, and decay stage and to a lesser degree also by percentage of trunk contact with the soil and cover of mosses, trees, and shrubs. Resupinate fungi and fleshy saprotrophs were distributed along the entire decay gradient. Most polypores prevailed in early decay stages. Mycorrhizal agarics were associated with the latest stages. The presence of dominant species Fomitopsis pinicola had a low effect on the composition of other fungal species on the same trunk, whereas Phellinus nigrolimitatus had a significant effect. The monitoring revealed 71% of species known at the locality from spruce, and 45 species new to the locality, especially those with inconspicuous fruit bodies. The previously published field survey was more efficient for capturing rare species with larger fruit bodies. Both methods should be combined during mycobiota inventories.