Zur Geschichte der mitteleuropäischen Trockenrasen seit dem Spätglazial - Methoden, Tatsachen, Hypothesen
[On the history of Central European dry grassland communities since the Late-Glacial - methods, facts, hypotheses]
Literature surveys reveal, that our present knowledge of the formation of dry grasslands is sparse compared to that achieved for woodlands, mires and arable lands. (Under dry grasslands we mean the communities of the classes Violetea calaminariae, Sedo-Scleranthetea (Koelerio-Corynephoretea), and Festuco-Brometea). Still there are a number of sources which can quite rigorously be evaluated actualistically. These are listed in Table 1, and in the text they are interpreted specifically with respect to dry grasslands. The likelihood of an air-tight preservation is very low. Where found at all, these are as a rule thanatocoenoses. However, current chorological disjunctions, the present plant sociological behaviour, and archeological as well as historical finds also permit - with measured scientific imagination - some critical conclusions to be drawn. These will be presented in a chronological sequence. Among the subfossils of the Late-Glacial (ca. 16 000-10 000 BP) and the early Post-Glacial numerous species can be found which may be regarded as playing a role for the synevolution of the dry grasslands. One also finds disjointedly distributed present-day continental or alpine species pointing in the same direction. These can also be regarded as representatives for many other species with present-day continuous areals. Endemic heavy-metal plants are to be interpreted as Late-Glacial derivatives of previously widely distributed ancestral species. For the Neolithic and Bronze Ages no meadows can be demonstrated; although domestication of animals is unequivocal, the question of the nutrition of the livestock presents itself. Feeding with leaves and brushwood has been quite recently established. Stubble grazing can also be assumed to have been practised. Of course, forest grazing in prehistoric times has been long established. However, actualistic studies on the syndynamics of the vegetation at the sites of forest clearings in primeval forests are lacking. In fact the grazed forests studied today in Central Europe are actually stands in progressive succession. Nonetheless, several dozen subfossil plant species taken together indicate that there were nutrient-poor and dry grasslands already developed. Here it is unclear to what extent true community mosaics vs. "mixtures" ("Durchdringungen") were involved. The proportion of "Saum" ("border") species in the available material is high, which indeed points clearly to a very extensive grazing. From the Iron Age there is available to us in one fortuitous instance a dry grassland-palaeobiocoenosis, autochthonous, from the covering of a burial mound for a Celtic "prince" (from the 6th century BC). This has been evaluated in impressive detail (encompassing ca. 85 species) and in comparison to present-day neighbouring dry grassland communities. The similarity between the old species combination in situ and the present-day vegetation is striking. Thus the nucleus of the anthropozoogenic Brometalia in their pasture form were already demonstrably developed in Germany at that time. Corresponding mown stands have not so far been detected. In any case, they presumably must have been quite scarce until at least the Middle Ages.