Oxbow Lakes: Vegetation History and Conservation

Abstract

Along the heavily regulated Drava River, oxbows were formed by meander cut-offs in the first half of the 19th century. Now they are biodiversity refugia in an environment dominated by agricultural fields. Main seminatural vegetation types of the oxbows are euhydrophyte vegetation, reed and cattail beds, tussocky and non-tussocky large sedge beds, grey willow shrubs, and riparian willow-poplar or alder forests. The majority of oxbows harbour eu- or mesotrophic habitats. Oligo- and dystrophic habitats are far less common, endangered and protected. The aquatic and riparian vegetations of the oxbows of the Drava floodplain are relatively well-preserved, due to moderate land use, state-border position for fifty years, and partly National Parks status for 20 years. Since Hungary’s accession to the European Union (2004), habitats and sites of European Community importance (Natura 2000) are the priorities of nature conservation. The main threat to oxbows is hydroseral succession, accelerated by riverbed incision, drought hazard and dropping groundwater levels. Other threats are excess nutrient load, spread of invasive species and oversized large game and herbivorous fish populations. For the sustenance of floodplain wetlands intensive, multi-sided and coordinated conservation measures are needed.