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coarse screes often remain unfilled by fine grained matrix and they contain autochtonous forest molluscan fauna. These circumstances prove (1) rapid,¹ sometimes ‘‘catastrophic” formation of screes due to the rock falls, (2) these changes were taking place still in forested environments and thus without significant anthropic impact. Some of the morę demanding species like Mac-rogastra densestriata, Macrogastra latestriata, Truncatellina claustralis and at some places Bulgarica cana, Carychium tridentatum are retreating, but on the other hand some species of grasslands including modem elements that have never lived in Central Europę before(Oxychilus inopinatus - sińce Neolith-ic, Cecilioides acicula - undeground species). For these reasons we consid-er the Subboreal from the point of Holocene biostratigraphy as the initial phase of the Late Holocene diversity depletion (Lożek 1982).

The Subboreal may be regarded as a kind of a boundary in some Mid-European regions or landscape elements, because of the irreversible relief and soil changes taking place. Severe erosion leads to formation of fiat floodplains because of the enhanced accumulation of floodplain loams (Auelehm). Tufa bodies were affected by downcutting, several meters deep gullies developed at many different places. The dramatic change that may be depicted as “Lu-satia crisis” was taking place in sandstone areas (Lusatia culture represents one of the most widespread cultures of the Late Bronze Age). The older Pre-Subboreal sand strata are calcareous and may contain as many as 40 molluscan species including demanding forest species, while younger sediments are acidic and oligotrophio - the diversity is significantly reduced to 5-7 envi-ronmentally indifferent species that have survived in these areas till now. The leaching of calcium carbonate had a profound effect on the vegetation - the original mostly deciduous beech and oak woods were transformed into pre-vailing oligotrophic pine forests. Fortified settlements were for the first time located in mountainous regions close to the tree limit, sometimes 1200-1500 m above sea level (Południca in Nizke Tatry Mts., Slovakia - Pieta 1981).

The further biodiversity deterioration continued through the Subatlantic when some morę demanding molluscan species disappeared. Last centuries before our era are characterized by morę humid, colder climate and partial reforestration of hilly regions. Great migration took place during the l-6^,h century when it was concluded by the Slavic arrival around 540 and then 590 (TfeStik 1997). The Slavs occupied at the beginning the old loess-chemozem settlement area, but during the 10^,h century and later they spread over most of the still virgin landscape including mountainous regions. Mining coloni-zation played an important role in the Bohemian mountains, but pastorał Yalachian colonization was even morę intensive in the Carpathian mountain