Sandökosysteme in Südhessen: Staus quo, jüngste Veränderungen und Folgerungen für Naturschutz-Maßnahmen

2000

S. 25-45

54 Lit. Ang.

Unselbständiges Werk

200063705

The open sand sites in south Hesse, especially in the region of Darmstadt, still contain a number of endangered vegetation types (e.g. Bromo tectori-Phleetum arenarii, Armerio-Festuccetum trachyphyllae), as well as larger populations of endangered plant species (e.g. Jurinea cyanoides, Bassia laniflora). Many sites with their endangered ecosystems are meanwhile so small and fragmented that an exchange of diaspores is currently hardly possible any more. Data on soil seed banks and seed rain show that in no case endangered species of sand ecosystems were present in the seed banks of more ruderalized areas. All Red Data Book species found in the seed banks of different pioneer stages, the Jurineo-Koelerietum glaucae, and the Armerio-Festucetum trachyphyllae occur in the actual vegetaion too. For pinoneer habitats it could be shown that the seed bank plays a role in the restitution after disturbance for some species (e.g. for Corynephorus canescens and Potentilla argentea). It is doubtful whether all the present micropopulations of endangered species will survive. The pine stands, which in 1950 were still rich in Pyrolaceae and Orchidaceae species, have considerably changed and are meanwhile with regard to these characteristic species florstically impoverished. Their herb layer is nowadays often characterized by dominant stands of taxons of the Rubus fruticosus group and by Calamagrostis epigejos. Some releves of the florstically impoverished Pyrolo-Pinetum and Leucobryo-Pinetum are presented. but also at open land sites, mono-dominance stands of Poa angustifolia, Calamgrostis epigejos and, in the recent past, an increase in the C4 grass Cynodon dactylon have been ascertained, especially when the land was not utilized. It will be shown that many of the particularly endangered sand ecosystems are mosaic complexes which need certain disturbance factors to be preserved also in their pioneer stages. Disturbances retard long-term changes (e.g. caused by eutrophication) and make it thus possible to "redynamize" the areas. A promising approach is for instance grazing by extensive breeds (sheep, goats, pigs); grazing animals promote dynamic processes.