Impoverishment of recent floodplain forest mollusc fauna in the lower Ohre River (Czech Republic) as a result of prehistoric human impact
Abstrakt
Analyses of fossil mollusc successions have rarely been used to study the development of floodplain forests during the Holocene. The Ohe River, located in a prehistorically settled chernozem area in the Czech Republic, is partly situated in Cretaceous marlstones, yielding sediments suitable for fossilization directly in floodplain deposits.
We analysed five fossil mollusc successions situated in the lower stretch of the Ohe River and compared the results with recent mollusc assemblages studied along the entire 256km of the river. Fossil samples were composed mostly of open-country species throughout the Holocene or the whole preserved succession.
Only some samples also contained woodland assemblages, but these were always greatly impoverished, with a very low frequency of strictly woodland species. Although the natural-looking appearance of the present-day floodplain forests of the lower river stretch has resulted in its being declared a nature reserve, modern floodplain forest mollusc assemblages there are also impoverished.
This reduction in the distribution of strictly woodland species compared with modern assemblages in the upper stretch of the river seems to be the result of an ancient human settlement and continuous disturbances of the floodplain forest development since the Neolithic. Thus, fully developed floodplain forest assemblages occur recently only in the upper non-impacted stretch of the river.
Based on the studied fossil successions we can conclude that the lower Ohe River floodplain was probably a mosaic of open and disturbed forest habitats throughout the Holocene. This area is part of a central European landscape island, where forests probably never fully developed and open patches from the early Holocene continually developed into an agricultural landscape.