Etablierung von Zielarten des Cirsio tuberosi-Molinietum nach Bodenabtrag im Bereich von entwässerten Altneckar-Schlingen (Hessen)

We studied whether target species of the Cirsio tuberosi-Mohnietum can establish themselves after restoration measurements in former riverbed sites of the Neckar (administration district Darmstadt-Dieburg, Hesse). These wetland sites (partly former fens) had been drained with subsequent mineralization of peat. We ran topsoil removal experiments to decrease nutrient values in the topsoil layer and to detect the optimal hydrological conditions for Cirso-Molinietum species. As target area we used the nature protection area "Monchbruch" (south of Frankfurt / Main) with extensive stands, e.g., of the Cirsio-Molinietum. In this pilot study we analysed germination, establishment, and vitality of four target species (Carex tomentosa, Cirsium tuberosum, Galium wirtgenii and Linum catharticum) from 2006 to 2009. We ran a field experiment with a gradient of soil removal between 25 cm and 100 cm depth with addition of seeds of these target species. Besides these species, we analysed the floristic structure of the spontaneous vegetation and the establishment of a seed bank. Additionally, we used a second site to study topsoil removal of 10 cm. While target-species germination and establishment rates were both low at a soil removal depth of 10 cm, they were high at 25-40 cm depth. Carex tomentosa was not able to germinate and establish in the dryer parts of the gradient, whereas too-wet conditions with long, persistent watering were not tolerated by Galium wirtgenii and Linum catharticum. Cirsium tuberosum occupied an intermediate position. An optimal establishment rate and vitality of the four target species was attained between 25 and 40 cm soil removal depth. In the course of our four-year study we documented the spread of the target species as well as the beginning of the establishment of a seed bank. Meanwhile many of the former riverbed stands are grazed (partly in a mixed grazing-/ mowing system). Therefore, we asked if an establishment after endozoochorous dispersal by sheep is possible. In this second experiment, sheep were fed seeds of three target species (Carex tomentosa, Galium wirtgenii, Linum catharticum). Only Galium wirtgenii clearly germinated and established successfully. For Linum catharticum we were not able to exclude secondary inoculation. At least for Galium, sheep may play a role as vectors for diaspore transport between the areas. Further investigations will analyse the possible establishment of the Cirsio-Molinietum after inoculation with mown material of this community