Hoverfly assemblages in the NP Gesäuse

Dealing with the effects of past human influences poses a challenge for many national parks. In the course of economic forest use in earlier times, the natural beech-tap spruce forests in the NP Gesäuse (Steiermark, Austria) were replaced by spruce forest in many places. Today, the rejuvenation of the beech is promoted through targeted management measures. Knowledge of local flora and fauna is of great importance for the planning and monitoring of such interventions. In the course of this study, suspended beds were therefore used as bioindicators for intact forest ecosystems. They include some xylophage species with good indicator properties. In order to draw conclusions about the quality of the habitats as well as the species richness of this group in the NP Gesäuse, natural beech (taps) spruce mixed forests, former spruce forests and through these running avalanche channels were investigated. The floating-fly communities were sampled and compared from May to August 2013 using a butterfly net and color shells. A total of 102 species were detected with 1841 individuals, including the first discovery of xanthogramma stackelbergi for Austria. The floating air communities of each habitat differed significantly, so that indicator species for each habitat type could be identified. In avalanche channels, with their rich flower supply, most species and the highest diversity could be detected. In the cool spruce forest, which served as a retreat from the heat on hot summer days, most individuals were caught. Differences in diversity and species richness between the two forest types were less clear. Although spruce forests showed the least balanced dominance conditions, they were a suitable habitat for many species due to the light conditions favourable by the management measures. Beech spruce mixed forests showed the highest variation in species and individual richness and housed most xylophage species, suggesting an intact forest ecosystem. Temperature and flower supply had a significant influence on floating fly activity and were used to explain differences in species richness and abundance between habitats. In comparison with the fishing methods, the butterfly net proved to be more efficient in terms of both species and individual numbers. However, since the species composition differs significantly between the two methods, the net cannot completely replace the color shells.