Spatio‐temporal habitat dynamics in a changing Danube River landscape 1812—2006

Modern, holistic concepts dealing with river/floodplain ecology recognize the key role of hydromorphological turnover processes for the development of distinct habitat patterns. Such patterns, in turn, are a vital basis for the extraordinary biodiversity of riverine systems. Natural braided/anabranched river systems in particular are characterised by high turnover rates; in the mid‐term, however, they are thought to stay in dynamic equilibrium (shifting‐mosaic steady‐state) as long as the physical framework conditions remain unchanged. This study analyses both the historical composition and the spatio‐temporal development of riverine habitats associated with an anabranched section of the Austrian Danube River. A habitat age model was used to analyse the age structure of the different habitat types. The results for the period 1812–1821 prior to channelization indicate that terrestrialization and habitat ageing were almost balanced with habitat regeneration and rejuvenation. Even though intensive morphological changes occurred, the Danube here largely persisted in dynamic equilibrium. The first channelization measures between 1821 and 1838, when 21% of the main channel banks were embanked, slightly promoted habitat regeneration. From 1859 onwards (80% embanked) until 1925, the natural habitat life time cycle was disrupted and the regenerating processes almost ceased. Altogether, human interferences led to a river landscape in a morphologically static state governed by significant terrestrialization (habitat succession) and habitat ageing. Without natural disturbances or, alternatively, targeted habitat management strategies, such an ecosystem soon lacks morphologically young habitats and adequate site conditions for a river/floodplain type‐specific biocoenosis.