“Heißländen” are dry sites in river floodplains, where rare, endangered species often occur. This thesis deals with Heißländen in the Natura 2000 site Tullnerfelder Donauauen in Lower Austria. The highly regulated river Traisen is to be renaturalized and environmentally improved in the course of a LIFE + project. The aim of this thesis was to characterize the vegetation of the Heißländen, as well as to determine their potential endangerment by both the impending renaturalization of the river Traisen and by succession. In order to determine vegetation units and to analyze the floristic composition, the vegetation was mapped using phytosociological methods. Some of the habitat types are endangered and several species are on the Red List of locally endangered species. The vegetation of the Heißländen resembles a mosaic structure and differs on a small scale, which made it difficult to determine distinct vegetation units for specific areas. Brometalia erecti and Festucetalia valesiacae are the most dominant occurring phytosociological orders. Valuable relics of steppic grasslands, with e. g. Stipa joannis, occur on a very small scale and there are also areas that are subject to scrub encroachment. Parts of valuable semi-natural dry grasslands are endangered through the implementation of the planned renaturalization of the river Traisen, which could only be saved by an alternative river route. There is also the risk of increasing encroachment of land, e. g. by Calamagrostis epigejos and various shrubs. In order to protect the valuable, partly endangered habitats and species of these Heißländen, a management plan must be developed, which takes into account the mosaic structure of the vegetation. Measures for the conservation of Heißländen include regular mowing and scrub clearance.