Bidentetea-Arten an der mittleren Elbe : Dynamik, räumliche Verbreitung und Soziologie
The ecology of species of intermittently flooded nitrophilous annual communities (class Bidentetea) is investigated intensively at the banks of the river Elbe since 1993, some aspects even since 15 years. The investigations show clearly, that area, development and diversity vary year by year. The main reasons are different weathers which cause time and dimensions of the high waters. The period of investigation however is still to short to decide whether it is a fluctuation or a straightened development, especially because the yearly variations are overlapped by the irregulär spreading of alien species. The analyses of the drift lines and similar Sediments show that high waters are of great importance for the spreading of Bidentetea species at the river Elbe. After floods it was even possible to find germinable diaspores in the Sediments deposited in Elm-Oak woods. The invasive plants fit till now well in the existing plant communities, a displacement of native species was not obeserved. The distribution in area and time of all Bidentetea species for a large river section is shown for the first time in this paper, the actual ecology of the invading species Artemisia annua, Artemisia biennis, Bidens connata, Bidens radiata, Portulaca oleracea, Rumex stenophyllus and Xanthium albinum is also documented.