An analysis of factors influencing the diversity of macrofungi fruiting on decaying beech logs at site level is presented. Variables related to log size and shape and decay stage were found to explain up to 56% of the variation in total species richness and 42% of the variation in the richness of threatened (red-listed) species. Inclusion of variables relating to the vernal flora and the degree of soil contact further increased the explained variation in total species richness to 71%, but these variables were non-significant with respect to red-listed species. However, inclusion of the variable log type, distinguishing uprooted logs, logs broken at root neck and logs broken 1–7 and 8–15 m above ground, increased the amount of explained variation in richness of red-listed species to 50%. Among the log size and shape variables, the number of bole forks was superior in describing the variation in both total and red-listed species richness. Accordingly, forked trees should preferably be selected for decay in order to improve biodiversity, since they support comparably higher species diversity than unforked logs and have limited economical value. The importance of log type for the richness of threatened species appears to be connected with the occurrence of certain non-dominant primary decayers, causing heart rot, subsequently allowing the establishment of red-listed species. Accordingly, it is suggested that a high diversity of primary decayers may be a key to the conservation of wood decaying fungi. Microclimatic variables were found to have a limited effect on fruit body diversity on the studied logs; however, the microclimatic regime is discussed as an important factor in relation to management of dead wood for fungal biodiversity Español