Diversity and composition of dead wood inhabiting fungal and bryophyte communities in semi-natural beech forests in Europe

Species composition and diversity of fungi and bryophyte communities occurring on deadbeech trees were analysed in five European countries (Slovenia, Hungary, The Netherlands,Belgium and Denmark). Altogether 1009 trees were inventoried in 19 beech dominated forestreserves. The realized species pool of fungi was approximately three times larger than that ofbryophytes (456 versus 161 species).

The two most important factors influencing the composition of both fungal and bryophyteassemblages were decay stage of the trees and geographic region. In the case of fungi theeffect of decay stage exceeded the effect of geographical difference, whereas in the case ofbryophytes it was the opposite. For both organism groups species richness per tree waspositively associated with tree size. In the case of fungi obligate wood decaying speciesdominated the studied communities in all countries. Bryophyte communities were composedof species belonging to widely different ecological groups. The proportion of epixylic specieswas higher in Slovenia than in Hungary (more continental climate) and in the Atlantic region(lower naturalness of sites). The significance of bryophyte taxonomic groups changed withcountries: in Slovenia hepatics, in Hungary and Denmark pleurocarps, and in TheNetherlands and Belgium acrocarps were the most important.

Diversity of communities differed considerably among regions. Slovenian sites were thehotspot of bryophyte diversity characterized by high alpha (species richness of trees) and beta(species richness of sites) diversity and a high fraction of rare and threatened species. Fungalalpha diversity is low, but beta diversity is high with rich occurrences of infrequent andthreatened species. This richness is most likely caused by the combination of high airhumidity and a very high degree of naturalness of the Slovenian sites. Hungarian stands arecharacterized by intermediate levels of fungal alpha and beta diversity, intermediate to ratherhigh levels of bryophyte alpha and beta diversity, and very high fractions of rare andthreatened fungal species. These characteristics reflect the relatively high naturalness of thestudy sites, as well as a rather continental climate. In the Danish sites alpha and beta diversityof fungal assemblages, as well as the number of infrequent species was high, while thenumber of threatened species was intermediate. For bryophytes, alpha diversity was low andbeta diversity was intermediate. These characteristics are explained by a combination offorest history, present forest structure and climatic traits, and show that Danish beechreserves have a good potential for restoring rich bryophyte and fungal communities if more orbigger forest reserves are declared. The Belgium site was characterized by high alpha, butlow beta fungal diversity, and intermediate alpha, but low beta bryophyte diversity, and arather low frequency of threatened species. These patterns seem to reflect the favourableclimate for growth in combination with severe impact from past human disturbance. TheDutch sites are characterized by low fungal alpha and beta diversity, and low bryophytealpha, but intermediate beta diversity, and very low frequencies of threatened species in bothgroups. These characteristics clearly relate to the low degree of naturalness of the beechforests in The Netherlands.