Due to changes in cultural landscapes which intensified the land use within the second half of the last century, the vegetation of extensively managed moist grassland became more and more endangered. Melioration as well as strong nutrient inputs by fertilisation changed the site conditions to productive, intensively managed grassland with an often species-poor vegetation, dominated by species of the family Poaceae. Because of the high phytodiversity and the many endangered plant species in the remaining extensively managed moist grassland areas, protection and restoration of these areas have become the focus of scientific studies and restoration projects. An unfavourable water regime as well as a high nutrient availability are abiotic obstacles, while seed limitation caused by the lack of populations and a high fragmentation of the plots are biotic obstacles to the restoration. Therefore, adequate restoration methods and an adjusted management of the areas are important conditions for the protection of extensively managed grassland with a high nature-conservation value. Within the scope of the testing and development (T+D) project “Ried und Sand”, investigations of the management and restoration of grassland areas in the “Hessian Ried” were carried out in the area of former meanders of the Neckar. Cirsio tuberosi-Molinietum vegetation in the nature protection area “Mönchbruch” served as a target area. The aspects treated in this thesis are related to the development of the vegetation in extensively grazed areas, the quantity and quality of the phytomass with respect to animal nutrition, and the establishment of target species (by means of topsoil removal and experimental transfer of different types of inoculation material) on species and community levels. The investigation of the vegetation (Chapter 3) succeeded in specifying the main site-conditions as well as the effects of extensive grazing and moderate restoration methods on the investigated plots. The differences in soil moisture of the plots, which are reflected in the composition of the vegetation, could be ascertained by perennial measurements. Additionally, a productivity gradient could be defined with reference to the target area. Investigation on standard plots showed that sheep grazing maintains the vegetation structure and tends to increase phytodiversity. On fallow land, a rapid succession occurred, which led to litter accumulation, reduction of grasses, increase of herbs and formation of a shrub layer. Grazing is an appropriate measure to ensure an open landscape, but it did not result in the establishment of either Molinion and Molinietalia species or endangered species. The effects of cattle grazing were very different. On one site the grazing intensity was so low in the plot areas that it didn’t have consistent effects and fallow stages occurred which maintained the status quo. The species number showed a small increase, or at least no decrease, compared to control plots. However, rare or endangered species were not favoured. Moderate restoration methods with a slight topsoil removal and inoculation led to an increase of phytodiversity due to an establishment of ubiquitous grassland and ruderal species, but only very few target species. When the rotary tiller was employed instead of topsoil removal, the effects were less pronounced and phytodiversity was also slightly increased. On young ex-arable land, succession led from a stage of annual weeds and ruderals to a stage with perennial ruderals and to stands which were dominated by graminoids. Inoculation brought about a considerable increase in species number, but mostly of widespread grassland species. Another aspect of extensive grassland management is a balanced livestock nutrition which guarantees health and welfare of the grazing animals in the long run. This depends on the quantity as well as the quality of the available phytomass and can probably be improved by an adjusted grazing management. As part of this thesis, the phytomass production and its quality at the time of peak standing crop of different grassland types in the “Hessian Ried” and a target area was investigated (Chapter 4). Vegetation parameters, phytomass production as well as ruminal nitrogen budget (RNB), contents of crude fibre, crude protein, minerals (calcium, potassium, magnesium, sodium and phosphorus) and energy content (metabolizable energy, net energy content for lactation) of the vegetation of different grassland types and the target area were analysed. The grassland types were only slightly different and the animal nutrition could be qualified as good, sometimes with an insufficient availability of sodium and phosphorus. Ruderalised areas showed an increased nitrogen content, which can be toxic in some cases. The target area was characterised by a lower phytomass production and slightly reduced crude protein contents, RNB and contents of potassium and phosphorus compared to the “Ried”-areas. In case the target communities are restored in only small areas of the “Hessian Ried”, remaining grassland areas can compensate a possibly insufficient supply of phosphorus and sodium and thus enable long-term management within the grazing system. In the case of a grazing system including “Ried” and “Sand” areas within the investigation area of the Testing and Development-Project “Ried und Sand”, the “Ried”-areas play an important role for animal nutrition. Abiotic factors such as nutrient availability as well as biotic factors such as seed limitation are to be considered for the restoration of grassland. In a pilot study we analysed germination, establishment and vitality of target species depending on topsoil removal depth (Chapter 5). Seed addition was arranged on a gradient of soil removal and topsoil-removed plots. Besides the development of these single species, we analysed the floristic structure of the spontaneous vegetation and the establishment of a seedbank. Germination and establishment of the seeded target species was mainly successful in all approaches. Target species germinated and established themselves weakly at a soil removal depth of 10 cm, but very successfully 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 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. Only Galium wirtgenii clearly germinated and established itself successfully after endozoochorous dispersal by sheep. Carex tomentosa didn’t germinate and for Linum catharticum we were not able to exclude secondary inoculation. At least for Galium sheep may play a role as vectors to guarantee diaspore dynamics between the areas.
We further investigated the biotic measure of inoculation of a Cirsio tuberosi-Molinietum to overcome seed-limitation on community level after topsoil removal in the area of the “Hessian Ried” (Chapter 6). The inoculation was carried out with fresh mown or raked material. In addition to the establishment of the target community, the potentials of different inoculation materials, including the diversity of their species-pool, could be assessed as well. The experimental design comprised two inoculation stripes and one control stripe on a restoration site with previous topsoil removal. The establishment of target species of the Cirsio-Molinietum was monitored in both inoculation approaches after two years. In the first year a clear emergence of target species was recorded, whereas next year a small decrease occurred, probably due to wet weather conditions and prolonged inundation events. Therefore, there was a development of stands with wet soil conditions. Comparison of the two inoculation materials showed a higher restoration potential of raked material, which had a higher diversity of seed species. This is probably caused by the retention of seeds in the bryophyte and/or litter fraction of this inoculation material. In contrast, mown material contained partially a higher abundance of target species, which fructified at mowing date. Further monitoring of the established populations of both experimental approaches seems advisable, because the development is probably not yet completed after two years. An appropriate extensive management of the site, e. g. a mowing-grazing system, is also necessary to ensure the development and survival of the established target plant community. Altogether this thesis shows that an extensive grazing management can maintain the structural status quo of grassland areas in the “Hessian Ried”, which is characterised by the predominant water regime and high nutrient availability. These grassland areas provide good animal nutrition and can compensate for grassland with phytomass of less nutritional quality but with higher conservation values, such as sand-ecosystems, within one grazing system. A significant improvement of nature conservation values and an increase of phytodiversity could not be guaranteed by the management. Here, the restoration methods topsoil removal in combination with the transfer of inoculation material can lead to an establishment of the target-community on species- as well as community-level. Especially the transfer of raked material is a promising method. The possible connection of such scattered restoration areas by the existing grazing system guarantees animal nutrition and can improve further grassland areas in the “Hessian Ried”, e. g via endozoochory. In the grazing system of the T+D-project the existing grassland areas can compensate for the lower phytomass production and quality of sand ecosystems with high nature conservation values, and thus improve the conditions of the whole grazing management. | English |