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Abstract Nowadays Najas flexilis is believed to be extinct in Poland, Germany, and Switzerland, while in other European countries it is classified as endangered or vulnerable. During the Early and Middle Holocene the species occurred throughout much of Europe, but in the Late Holocene it underwent a significant decline and reduction in range following, as it is believed, the gradual cooling of the climate and/or the eutrophication and acidification of lakes caused by human activity. The article recognizes the existence and disappearance of slender naiad in the palaeolake at the Hieronimowo site, NE Poland, during the Eemian Interglacial and at the beginning of the last glaciation (Vistulian, Weichselian), when lake transformations were caused solely by natural factors without human impact. Results of palynological and macrofossil analyses reveal that the appearance of slander naiad in the studied water body was probably triggered by the change of its pH and trophic status, resulting from the start of spruce and pine expansion stimulated by climate worsening during the younger part of the hornbeam phase (E5 R PAZ) in the middle Eemian. The appearance of spruce and pine in the area of the lake led to its acidification and oligotrophication, and that caused the strong and rapid development of N. flexilis. The species existed in the palaeolake at the Hieronimowo site through the spruce (E6 R PAZ) and pine (E7 R PAZ) phases, until the end of the Eemian Interglacial. These observations suggest that regressive transformations of the environment typical for the late part of the interglacial cycle, 'unsupported' by human activity, do not lead the extinction of N. flexilis. Quite the opposite, these processes promote this species. Its disappearance started only at the beginning of the Early Vistulian (Weichselian), and it was probably caused by a drastic decrease in temperatures and/or by the development of green algae, which limited light availability on the bottom of the water body. [ABSTRACT FROM AUTHOR]

Pollen analysis of sediments from three lakes and analysis of plant macroremains including charcoal from archaeological sites in the Mazurian Lake District provide new data for the reconstruction of vegetation changes related to human activity between the 1st and 13th century ad. At that time settlements of the Bogaczewo culture (from the turn of the 1st century ad to the first part of the 5th century ad), the Olsztyn Group (second part of the 5th century ad to the 7th or beginning of the 8th century ad), and the Prussian Galinditae tribes (8th/9th-13th century ad) developed. The most intensive woodland clearing occurred between the 1st and 6th/7th century ad. Presence of Cerealia-type, Secale cereale and Cannabis-type pollen, as well as macroremains of Hordeum vulgare, S. cereale, Triticum spelta, T. cf. monococcum, T. cf. dicoccum, Avena sp. and Panicum miliaceum documented local agriculture. High Betula representation synchronous with microcharcoal occurrence suggests shifting agriculture. After forest regeneration between c. ad 650 and 1100, the area was strongly deforested due to the early medieval occupation by Prussian tribes. The archaeobotanical examination of samples taken in a cemetery and a large settlement of the Roman Iron Age revealed strong differences in the taxonomic composition of the fossil plant remains. An absolute dominance of birch charcoal in the samples from the cemetery indicates its selective use for funeral pyre construction. There is a difference between cereals found in both contexts: numerous grains of Triticum have been found in the cemetery, while in the settlement crops were represented mostly by Secale and Hordeum. Grass tubers, belonging probably to Phleum pratense, are among the particularly interesting plant remains found in the cemetery. [ABSTRACT FROM AUTHOR]