Dead wood and moribund trees are characteristic structural elements of forests, providing a dominant resource of dead organic matter and special microhabitats. Many invertebrates are saproxylic, i.e. dependent on this resource either through trophic or topic (habitat) links. Many saproxylic species have become rare and threatened, often restricted to remnants of primeval forests. Most such stands exist in mountainous areas at higher altitudes while very few lowland forests have an unbroken history of existence and a close to natural state. However, in some floodplains of large rivers, forests did prevail throughout the ages. Today, floodplain forests are among the most endangered habitats in Europe. Data on the saproxylic fauna in floodplains is very limited. Since 1996, the saproxylic communities of some arthropod taxa (Aranaea; Coleoptera; Diptera-Brachycera; Hymonoptera: Formicidae) have been studied in old floodplain forests, dominated by oak and ash, in South Moravia (Czech Republic). Some aspects of species richness and the impact of inundation are presented.