Richness and composition of macrofungi on large decaying trees in a Central European old-growth forest: a case study on silver fir (Abies alba)

The species richness and composition of macrofungi on huge fallen trunks of silver fir (Abies alba) were monitored during a case study in the well-preserved Boubinsky prales virgin forest in Czechia. A detailed survey of all macrofungal groups recorded 200 species on 30 trunks within the diameter range of 85-190 cm. This number is very high in the overall context and includes many rare and threatened species. The species-richest groups were corticioids and fleshy saprotrophic fungi. Individual trunks were inhabited by 4-33 species. The species richness was negatively correlated with trunk decay and positively with bark cover, moss cover and trunk length. Simultaneously, it was negatively correlated with increasing time since tree fall, time since tree death and the way of fall, namely its category 'broken'. Species composition was significantly influenced by decay, bark cover, moss cover, and, to a lesser degree, also by canopy cover, time since fall and time since death. The best trunks in terms of mycobiota rarity and nature conservation were those which died a long time ago but fell to the ground only recently. They have gone through a long phase of slow decay and gradual succession in standing position. As a result, they are inhabited by many distinctive fungi, especially those preferring natural forests. Durandiella gallica, Hohenbuehelia josserandii, Panellus violaceofulvus, Phellinus pouzarii and Pseudoplectania melaena can be considered almost exclusive fir specialists. All these fir-associated fungal species are immediately threatened by the gradual disappearance of firs resulting mainly from ungulate overpopulation, requiring the urgent implementation of appropriate conservation measures. A list of fungi characteristic of wood of silver fir and Norway spruce is presented.