Interessante Molluskenzönosen (Mollusca: Gastropoda) aus dem südhercynischen Gebiet

Abstract

UNRUH, M.: Remarkable, interesting, gastropod assemblages from the region between middle Weiße Elster and Saale rivers in the southern hercynian region. – Hercynia N. F. 35 (2002): 253-274.In the south of Saxony-Anhalt, between the rivers Saale and Weiße Elster, mollusc coenoses have been examined in three forest habitats and blanket coverage mapping has been carried out. In a landscape characterised more or less by the absence of forests and by intensified agriculture the remaining more or less small-scale forests host highly diversified or more or less poorly diversified societies of land snailes depending on the intensity of use, quality of habitat and edaphic factors. Euryoecious widespread species in high abundance can be found on the locally levelled out podsol forest soil that is covered by forests of oak-hornbeam societies all of the same age. This coenose has been deduced from the Droyßig forest, a Circaea lutetiana subvariant of Luzulo-Fagetum. Here 21 different species of molluscs have been detected. According to SCHUBERT the soils of these forest societies are dry and acidified close to the surface. In the Zeitzer Forst (49 land snailes) and the Grabeholz (39 land snailes species), two differently sized neighbouring forest areas, mollusc societies have been found which beyond the only current proof of Daudebardia brevipes and Vitrea subrimata point out the steadiness of environmental factors for several centuries. These old forests are depicted in written sources and maps and in historic times formed the boundary of the natural fur-beech-forests. The presence of vegetable indicator organisms allows the reconstruction of the historic transformation of these deciduous forests with now dominant oak trees and other economically preferred forest trees that happened a long time ago. The special attractiveness of both places to molluscs is caused by such factors as the formation of sinter by emerging watercourses in a favourable microclimatic situation as well as by the continuing coverage by forests for centuries. Thus in the Zeitzer Forst and the Grabeholz singularities have been found regarding the continuity and quality of environmental gradients reaching far beyond the average of the more or less impoverished typical coenoses that are formed of euryoecious species. Yet it is not clear whether the great variety of species is a relict of a once more widespread coenose or whether it has emerged from the especially favourable complexity of an environment with a high percentage of dead wood, a favourable soil and the availability of chalk in a habitat normally characterised by more acid to neutral soil reactions. Taking into consideration the conditions of the habitat these mollusc coenoses can be regarded as reference habitats for the discussion of the indicator features of invertebrates for the assessment of historic old forests. The highly diversified and rare habitats which are also suitable as a refuge for other groups of organisms are part of the ”Aga- und Elster-Tal und Zeitzer Forst” nature reserve. Furthermore the Grabeholz was declared a ”protected forest area” in 1999 and the ”Zeitzer Forst”, an area of about 1.500 ha, is bound to be declared a nature reserve.