Abstract: Faunistic-ecological field investigations of the ant fauna (Hymenoptera, Formicidae) of a wild-river landscape in Tennengau, Salzburg. – In the summers of 1998 and 1999 the ant fauna of five successive stages of a natural floodplain – gravel bank, Salicetum eleagnii, Erico-Pinetum sylvestris, Alnetum incanae and a pine forest – situated in the Tauglgries, 4 to 5 km Se of Hallein, was investigated. Three methods were applied in this study: direct counting of ant nests, baited pitfall traps and additional sampling by hand. A total of 26 ant species (ca. 21 % of the Austrian myrmecofauna) out of 10 genera (Lasius, Formica, Camponotus, Manica, Myrmica, Leptothorax, Myrmecina, Formicoxenus, Tetramorium, Ponera) was identified in the area. The highest species number was found in the xerothermic Erico-Pinetum sylvestris (22 species). The average nest densities in the investigation areas were between 0.07 and 48 nests per 100 m2. The highest average nest densities and relative abundance achieves Leptothorax nigriceps in the Erico-Pinetum sylvestris (48 nests / 100 m2, which is 20 %), Manica rubida in the Salicetum eleagnii (38.7 nests / 100 m2, which is 35.3 %) and Ponera coarctata in the Erico-Pinetum sylvestris (34.7 nests / 100 m2, which is 14.4 %). The five study areas are described by the structure of vegetation, temperature, soil moisture and soil nitrogen (Ellenberg & al. 1991) and vegetation density. Furthermore the ecological characterization and analysis of autecological requirements concerning habitats for ants is given on the one hand by the division of ant species into the average of tolerance towards temperature, soil moisture, soil nitrogen and vegetation density, and on the other hand by the classification of habitats through the number of nests and species. Since natural floodplains in Central Europe are already rare and endangered, reasons for the need of protection are examined. The most important aim for protection is the preservation and the promotion of the great variety of habitats, as well as the numerous but already threatened species of animals (especially arthropods), which are especially adapted to xerothermic environmental standards.