Habitate und Vorkommen der Deutschen Ufer-Tamariske (Myricaria germanica (L.) Desv.): Vergleich zwischen Voll- und Restwasserstrecken

The habitat requirements of Myricaria germanica and the impact of the residual flow regime of hydropower plants on their habitats and occurrence was analyzed in Austria on three river sections within the influence of diversion plants and five river sections without. The ex-situ germination experiments showed that the germination of Myricaria germanica seeds began after only a few hours in the water and the seeds were germinated on average two days after the flooding. During the germination phase the German tamarisk invested little in root and shoot growth, but afterwards, the young plants showed rapid root growth. In general, the field survey confirmed that the success of establishment of Myricaria germanica was highest on sites which are more or less open, have high soil moisture and are also not significantly influenced by extrem morphodynamics. The analysis of the site con-ditions for the tamarisk showed only slight differences in the flow regime and the morphodynamics with regards to and without the influence of hydropower plants. The three residual flow sections were characterized by a clearly lower occurrence of the tamarisk, although river morphological aspects could also be a possible reason for this. In some sections (natural and residual flow) there was a low number of individuals of the seedling and establishment phase. This observation underscores the fact that a successful establishment of new tamarisk generations is not possible in all years. Additionally it should be noted, however, that changes in the flow regime caused by diversion plants can have a negative effect on the young development phases of tamarisks in small (regularly occurring) floods. In order to maintain sustai-nable tamarisk populations in residual flow sections, special attention must be paid to the continuous transport of bed load and in particular, the river bed forming discharges.