Mapping of the Xylobionten fauna in deadwood stands in the Gesäuse National Park

The objectives of the research project are the survey of the species of beetles and bedbugs colonising wood in the Gesäuse National Park, the representation of species diversity depending on, inter alia, forest type, altitude, exposure and deadwood abundance, the identification of particularly valuable forest habitats and, if necessary, the formulation of measures to increase biodiversity in the forest. Beetles were collected in June/July 2016 at 30 locations with the help of approach traps and bark bugs were recorded at 42 locations in 2017 in a time standardised manner. In addition, the bedbugs of the approach traps were also evaluated, which is why bedbug data for 53 locations are available. Data from the FFH habitat type map of the national park and from the forest inventory of the national park were included in the data evaluations. A total of 1,553 beetle individuals were collected, which can be assigned to 231 species from 52 families. 179 species are xylobiont. Among them are 65 fresh wood and 62 old wood settlers, 28 species of tree fungus-living beetles, 2 Mulmhöhlenbesiedler and one species with special biology The species set includes several faunistic and nature conservation biologically remarkable species: Symbiotes armatus (1. Evidence Stmk), Zilora obscura, Cacotemnus thomsoni (both 2. Evidence Stmk), Microrhagus lepidus (3. Evidence Stmk), Wanachia trigutata, Peltis grossa and Ostoma ferruginea. Also outstanding is the only second Styrian find of the very rare primeval forest relic Lacon lepidopterus. The species numbers per site vary greatly. On average, 15-30 species were found per site, the maximum value is reached with 39 species at the site Sheikkogel. The most species-rich sites are located on the one hand at south-facing, deciduous wood-dominated sites north of the Enns and on the other hand in the east of the national park at higher forest areas. Particularly species-rich forest types are spruce fir beech forests, the investigated snow heath pine forests and the subalpine spruce forests were relatively species-poor. The evaluation of the beetle communities showed the highest value level for four locations: Schagermauer, Gstatterstein, E Wirtsalm and E Sulzkarsee. The nature conservation value increases with the total deadwood volume and the volume of standing deadwood. For the national preservation of a number of extremely rare xylobionte animal species (e.g. Lacon lepidopterus) the national park probably has a special responsibility. Bark bugs were detected at 40 of the 53 sites examined. In total, eight species occur. Several species occur in the national park only from a certain stage of forest development and the available deadwood qualities. Crucial is the presence of dead wood in a stronger dimension and in the advanced phases of decay. The Styrian first detection of the extremely rare primeval forest relic species Cixidia lapponica (Nordic bark cicade) was also successful as bycatch. Probabilities of occurrence in the national park were modelled for four xylobionte, longitudinally value-determining beetles: Hylecoetus dermestoides (Lymexylonidae; freshwood colonizers), Melanotus castanipes (Elateridae; old wood settlers), Litargus connexus (Mycetophagidae; Mushroom colonizers) and Dolotarsus lividus (Melandryidae; forest relict species). The summation of the occurrence probabilities of these representatives of typical xylobionte guilds (beetles, bedbugs) provides information on the most valuable forest habitats in the national park for forest biodiversity. The study shows that valuable beetle and bark bug species in the national park only occur at a certain stage of forest development. Crucial is the presence of dead wood in a stronger dimension (30 cm diameter). High abundances were found by us on sites that had a deadwood stock of more than 70 m/ha, which is about three times the average deadwood stock in the Austrian forest.