DEVELOPMENT OF SMALL WATER-MIRE BASINS IN DURY RESERVE, NW POLAND K. Milecka G. Kowalewski

milecka@amu.edu.pl

Dury Reserve is located in Tuchola Forest, NW Poland. It consists of five small water-mire basins, which developed since the last glaciation.

Geological research revealed sequence of gyttja and peat layers accumulated as a result of lakes and mires existence. Pollen and plant macrofossil analyses let us to trace the development of regional plant cover and development of local water-mire ecosystems.

The bottom layer of the sediments reveals the vegetation at the hot period of Late Glacial, probably in the end of Allerod d. A pine forest dominated then with lower proportion of birch and light demanding herbaceous plants like Poaceae, Artemisia, Rumex and Cichorioidae. Younger Dryas is seen in the diagram very clearly with the high content of Juniperus pollen grains (ca 15%) and Betula (up to 55%). NAP exceed 20% because of numerous pollen grains of Poaceae, Artemisia, Chenopodiaceae, Rumex and Ranunculaceae.

Diminish of the curve of herbaceous plants signs the beginning of Holocene. Preboreal Period is mirrored in a very thin layer of sediments. High curve of Betula is still there, but Pinus pollen grains are more frequent instead of Juniperus and NAP. Density of the forest was growing then in comparison with the late glacial time.

The upper part of the core shows the accumulation of sediments in the time of great importance of deciduous forest at the area of Bory Tucholskie. At first Corylus immigrates and content of its pollen grains creates the highest curve. Later mesophilous trees like Quercus, Ulmus, Tilia and Fraxinus excelsior were more frequent.

There was no intensive human activity at the area surrounding Dury peatbog. The pollen diagram shows strong anthropogenic pressure on plant cover as late as in the uppermost part only. Since the Neolithic one can observe single or not numerous pollen grains of cultivated plants or pasture indicators. Bory Tucholskie were penetrated then, but settlement was not long lasting and frequent and signs of human activity came from sites of greater distance. More intensive economy of last centuries is reflected in several upper spectra mainly by content of pollen grains of Artemisia, Chenopodiaceae, Plantago lanceolata, Rumex and Secale.

The bottom part of the pollen dagram is probably not the beginning of the existing of organic sediments basin. High Pediastrum curve suggests the lake was formed some time before the accumulation of the oldest part of the core sediments. At the depth of 575 cm a clear change is marked. The lake finished its existence and bog was formed at the place of research core. Accumulation rate is much bigger in the upper part of core at the time of peatbog functioning. Sporomorphs of Sphagnum, Drosera rotundifolia and Lycopodium clavatum proves an oligotrophy of all the wetland area within Dury Reserve. In two short periods of lower water level, local culmination of Calluna vulgaris ocurred. Probably the less density of forest caused growing level of groundwater and rapid development of Sphagnum communities. The research is still going on.