Postglacial occurrence and decline of Betula nana L. (dwarf birch) in northeastern Poland

The Late Glacial and Holocene presence of Betula nana L. (dwarf birch) in northeastern Poland was reconstructed through palaeoecological analyses of sediment cores from the Taboły mire located in the territory of the Knyszyńska Forest. Peat records spanning thousands of years were analysed for plant macrofossils along with radiocarbon dating. Betula nana was present in Taboły from ca 13 000 to ca 9000 yr BP. The presence of this species was described in the Late Glacial period, most likely in the Allerød and Younger Dryas. However, our research on the palaeoecology of dwarf birch showed that after the Late Glacial/Holocene transition, the species did not disappear from northeastern Poland and still existed in the Preboreal, Boreal and lower Atlantic periods. The occurrence of Betula nana was documented by the presence of generative remains (nuts and catkin scales) in sediments, which is the best evidence of its in situ position. The later disappearance of the studied species could be related to the negative effects of palaeoenvironmental conditions in the Atlantic, which resulted in a temperature increase and high precipitation, causing the waterlogging of the substratum and rendering it unsuitable for dwarf shrub that prefers severe climate conditions. The Taboły site seems to be one of separate locations of B. nana during the Atlantic in this part of Europe.