Aim. Fungi are drivers of wood-decay in forested ecosystem, while bryophytes use dead wood as a platform for their autotrophic lifestyle. We tested the hypothesis that fungal communities on beech logs are mainly structured by substrate quality, while bryophyte communities are structured by climatic gradients. In addition we tested if community structure in both organism groups is altered along a gradient from nearly pristine forest to forests heavily affected by management and human disturbance in the past.
Methods. We surveyed 1207 fallen beech logs in 26 of the best preserved forest stands across six European countries, representing a gradient in overall naturalness of the forest landscape. Recorded species were classified in ecological guilds. Indirect ordination and variation partitioning was used to analyse the relation between species composition and environmental variables, recorded at log or site level.
Results. In total, 10,367 bryophyte and 15,575 fungal records were made, representing 157 and 272 species, respectively. Fungal communities were most clearly structured by substrate quality compared to bryophyte ones. In both groups a distinct turnover in species composition was evident along a longitudinal gradient from Central to Western Europe. Fungi specialised in trunk rot and specialised epixylic bryophytes were scarcely represented in Atlantic regions, and partly replaced by species belonging to less specialised guilds. Variables related to climate and forest conditions were confounded along this main geographical gradient in community composition
Main conclusions. We found bryophyte and fungal communities co-occurring on fallen beech logs in European beech forest reserves to differ in their response to biogeographical drivers and local scale habitat filters. Both groups responded to major gradients in climate and forest conditions, but the loss of specialist guilds in degraded forest landscapes points to a functionally important effect of forest landscape degradation at the European continental scale.