Epixylic diversity in an old-growth boreal forest is influenced by dynamic substrate attributes

Quantifying the factors influencing wood-inhabiting species in boreal forests is crucial for better understanding of their ecology and conservation needs. We estimated the influence of substrate attributes on epixylic diversity on logs of Picea abies, Betula pubescens, B. pendula, Populus tremula and Pinus sylvestris in a mixed European old-growth boreal forest with high substrate availability and continuity. The number of species of different taxonomic and substrate groups in respect of log attributes was estimated with generalized linear models. The composition of epixylic communities was analysed using non-metric multidimensional scaling with subsequent environmental fitting. Additionally, we calculated species interaction networks of log (tree) species and epixylic plants and lichens. Species richness per log decreased with the increasing height above the ground and increased with the increasing amount of accumulated litter. True epixylics were the most sensitive to a log position above the ground. Aspen and conifer logs harbored the highest richness of rare species of lichens and liverworts. Birch logs hosted mainly species with wide substrate amplitude. The whole epixylic community specialization index decreased in the order lichens, liverworts, mosses, vascular plants. Tree species identity and associated attributes (bark cover, pH etc.) as well as ‘dynamic’ attributes (accumulation of litter, wood decomposition and time since tree death) influenced the total species number, their taxonomic diversity, and the composition of epixylic communities. Our results indicate the importance of wood of various age and tree species for the conservation of epixylic diversity in boreal forests.