Natural Hazards Hazards for Nature? Avalanches as a promotor of biodiversity

Avalanches are feared by humans and considered catastrophic due to their unpredictable and destructive force. But this anthropocentric perspective fails to capture the potential ecological value of these natural disturbances. The Gesäuse National Park is a model-region for investigations of such highly dynamic events because of its distinct relief and extreme weather conditions. This project aims to record and analyse the animal assemblages in these highly dynamic habitats as well as document succession and population structure. 1) Dynamic processes lead to one of the very few permanent and natural vegetationless habitat types in Central Europe outside the alpine zone i.e. screes and other rocky habitats at various successional stages. In addition to the tight mosaic distribution of a variety of habitats over larger areas, avalanche tracks also offer valuable structures like dead wood and rocks. Remarkable is the sympatric occurrence of the three Harvestmen species Trogulus tricarinatus, T. nepaeformis and T. tingiformis, a species diversity peak of spiders, true-bugs and ants; and the newly recorded occurrence of Formica truncorum. 2) The presence of highly adapted species and coenoses reflect the extreme environmental conditions, specific vegetation cover and microclimate of these habitats. Several of the recorded taxa are rare, endangered and endemic. The very rare dwarf spider Trichoncus hackmani is a new record for Styria and the stenotopic and critically endangered wolf-spider Acantholycosa lignaria is dependent on lying dead wood. The true bug Phytocoris intricatus is a new occurrence record for Austria. The ant species Myrmica lonae is an extremely rare recorded ant species in Styria for which avalanche tracks are considered to be its preferred habitat. 3) Avalanche tracks in southern exposure are azonal heat islands providing suitable environmental conditions for thermophilic and heliophilous species as well as those normally considered to have more southern distributions. The surprising inneralpine presence of several southern and submediterranean species reflect these unique microclimatic conditions, e.g. the vulnerable spider species Atypus piceus and the grasshopper Myrmecophila acervorum. Furthermore, high alpine species disperse via avalanche tracks to lower-altitude sites. Some Arachnological examples are the mountain-jumping spider Sitticus atricapillus, Austrian subendemic gnaphosid spider Zelotes zellesis and the scree inhabiting wolf spider Pardosa nigra. Examples among true bugs more typical for subalpine grasslands include Calocoris alpestris, Nithecus jacobaeae, Eurydema rotundicollis and CARPOCORIS melanocerus. Avalanche tracks play a major role in the survival of rare and endangered arthropod species and coenoses and are important refuges of endemic species. Vascular plant diversity averaged 70 species per 20 m plot. Search biodiversity hotspots deserve protection. Avalance tracks are additionally considered essential corridors of vertical migration during periods of rapid climate change. While more research is needed to fully understand the ecological importance of these habitats, it is clear that acceptance and protection