Diversity and composition of dead wood inhabiting fungal and bryophyte communities

Abstract

Species composition and diversity of fungi and bryophyte communities occurring on dead beech trees were analysed in five European countries (Slovenia, Hungary, The Netherlands, Belgium and Denmark). Altogether 1009 trees were inventoried in 19 beech dominated forest reserves. The realized species pool of fungi was approximately three times larger than that of bryophytes (456 versus 161 species). The two most important factors influencing the composition of both fungal and bryophyte assemblages were decay stage of the trees and geographic region. In the case of fungi the effect of decay stage exceeded the effect of geographical difference, whereas in the case of bryophytes it was the opposite. For both organism groups species richness per tree was positively associated with tree size. In the case of fungi obligate wood decaying species dominated the studied communities in all countries. Bryophyte communities were composed of species belonging to widely different ecological groups. The proportion of epixylic species was 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 with countries: in Slovenia hepatics, in Hungary and Denmark pleurocarps, and in The Netherlands and Belgium acrocarps were the most important. Diversity of communities differed considerably among regions. Slovenian sites were the hotspot 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. Fungal alpha diversity is low, but beta diversity is high with rich occurrences of infrequent and threatened species. This richness is most likely caused by the combination of high air humidity and a very high degree of naturalness of the Slovenian sites. Hungarian stands are characterized by intermediate levels of fungal alpha and beta diversity, intermediate to rather high levels of bryophyte alpha and beta diversity, and very high fractions of rare and threatened fungal species. These characteristics reflect the relatively high naturalness of the study sites, as well as a rather continental climate. In the Danish sites alpha and beta diversity of fungal assemblages, as well as the number of infrequent species was high, while the number of threatened species was intermediate. For bryophytes, alpha diversity was low and beta diversity was intermediate. These characteristics are explained by a combination of forest history, present forest structure and climatic traits, and show that Danish beech reserves have a good potential for restoring rich bryophyte and fungal communities if more or bigger forest reserves are declared. The Belgium site was characterized by high alpha, but 4 low beta fungal diversity, and intermediate alpha, but low beta bryophyte diversity, and a rather low frequency of threatened species. These patterns seem to reflect the favourable climate for growth in combination with severe impact from past human disturbance. The Dutch sites are characterized by low fungal alpha and beta diversity, and low bryophyte alpha, but intermediate beta diversity, and very low frequencies of threatened species in both groups. These characteristics clearly relate to the low degree of naturalness of the beech forests in The Netherlands