The diversity of saproxylic beetles’ community from the Natural Reserve Voievodeasa Forest, North-Eastern Romania

Abstract

Nature reserves harbour considerable richness and diversity of saproxylic organisms since dead wood is preserved in situ, this being also the case of Voivodeasa beech-spruce-fir forest in North-Eastern Romania, the area investigated under the present research. Flight interception traps were employed to capture insects during a vegetation season with the goal to characterize saproxylic Coleoptera community in terms of diversity and several other structural features. Among the captured insects, the majority pertained to obligate saproxylic species (217 species). However, the unexpected high species richness corresponded to an area with modest representation of deadwood due to previous status of commercial forest. The identified beetles were members of different habitat-guilds depending on what type of substrate they colonized: recently dead wood (23%), decomposed dead wood (41%), wood inhabiting fungi (34%) and treehollow detritus (2%). According to their trophic position, the identified saproxylic beetles pertained to the following guilds: xylophagous (40%), mycetophagous (39%), predatory (14%), and species relying on other food resources. The observed richness corresponded to the case of hyperdiverse communities where sampling never leads to the stabilization of species richness under a realistic sampling scheme. The diversity profiles constructed on Shannon, Gini-Simpson, Berger-Parker and evenness indices for the pooled inventory and for separate samples across the vegetation season indicated the aggregated saproxylic community as highly diverse and highly uneven, with rich representation of rare species, dominated by few abundant species. We assembled four bipartite, unweighted, and undirected networks to approach the temporal changes across the sampling period extended over one vegetation season. The topology of beetles’ community and of the three main trophic guilds (xylophagous, mycetophagous and predatory) networks linked to time sequences are characterized by high connectance, high nestedness and modularity, with the exception of the mycetophagous sub-network not displaying significant modularity. Among the identified species, 13% indicate high degree of naturalness of the Voievodeasa forest. 62 of the identified species are included in the Red List of European Saproxylic Beetles of which five are near threatened (Protaetia fieberi, Cucujus cinnaberinus, Crepidophorus mutilatus, Ceruchus chrysomelinus, Prostomis mandibularis), Ischnodes sanguinolentus is vulnerable and Rhysodes sulcatus is an endangered species. During the study, two Coleoptera species, new for Romanian insect fauna were identified: Denticollis interpositus Roubal, 1941 and Hylis procerulus (Mannerheim 1823).