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The aim of this study was to make an evaluation of the current stands of a relict species, Salix lapponum, within the area of the Polesie National Park, to determine the population size and condition of downy willow as well as to analyse biocenotic conditions in its stands. The study, conducted in the years 2001–2003, allowed to establish that the number of S. lapponum stands had decreased significantly and that its population size in the confirmed stands in the Polesie National Park was substantially lower than 50 years ago. Salix lapponum was a component of different phytocoenoses, but its highest population size and a high degree of development were noted at the sites with the Betulo-Salicetum repentis and Thelypteridi-Phragmitetum communities. The character of the phytocoenoses in which Salix lapponum occurred in greatest numbers may evidence the wide range of tolerance of downy willow with respect to habitat conditions. There is a probability that not only the changes in its habitat conditions, which were noted over the last half-century, had a significant effect on the reduction in the number of stands and in the population size of this species. An essential problem appears to be the fact of the absence of flowering in individuals in many of the studied populations, which may result in an insufficient degree of adaptation of S. lapponum to changing habitat conditions.
Ostericum palustre Besser is a species protected by the domestic and EU laws. In Poland it occurs in about 150 sites one of which is located in the area covered by Natura 2000 “Lisi Kąt”. The population existing there, estimated as 35,000 individuals, covers the acreage of 342 ha. The species persists there mostly in over-dried and transformed-by-meadow-management reed beds with the share of Carex acutiformis and C. gracilis, in phytocenoses of Scheuchzerio-Caricetea nigrae with a large share of mosses, in overgrowing patches of the alliances of Molinion as well as sporadically within reed beds with Carex pseudocyperus. Its share in similar phytocenoses coincides with the reports in literature in the region of the Noteć Valley. In most cases those are heavily disturbed systems, transitional in nature, which must have been the reason for a relatively high level of species variation. The habitat preferences of Ostericum palustre, determined with Ellenberg's indicator values (L, T), correspond to the values optimal for the species. Soil, on the other hand, can be referred to as slightly acid, average fertile and mostly moist.
The present study showed the ecological differentiation of phytocoenoses dominated either by Myriophyllum alterniflorum or by Littorella uniflora, which in Poland are classified within the Myriophylletum alterniflori or Myriophyllo-Littorelletum association. The properties which best differentiated the waters of the above types of phytocoenoses were calcium and factors associated with the carbonate complex (pH, electrolytic conductivity, total and carbonate hardness), and pH in the case of substrates. The most distinct differences in the habitats were found between the phytocoenoses dominated by L. uniflora from the Pomeranian Lobelia lakes and those dominated by M. alterniflorum from the Łęczna-Włodawa Lake District, in which other species from the Littorelletea uniflorae class were absent. The L. uniflora phytocoenoses are associated with soft waters poor in Ca2+ and with the lowest values of pH, electrolytic conductivity, dissolved organic matter (COD-KMnO4) and dissolved SiO2. The substrates they inhabit are mineral and more acidic. By contrast, the values of the above-mentioned properties are considerably higher in the case of the phytocoenoses from the Łęczna-Włodawa Lake District. The habitats of the M. alterniflorum phytocoenoses from the Pomeranian Lobelia lakes occupy an intermediate position and are more similar to those of M. alterniflorum from the Łęczna-Włodawa Lake District. The results obtained in this study suggest that the phytocoenoses of L. uniflora and M. alterniflorum should not be included in the same association. Further studies are, therefore, necessary to resolve this problem. The comparative analysis of the present ecological findings and data obtained from other regions of Europe show that in Poland the phytocoenoses dominated either by L. uniflora or by M. alterniflorum, in which the contribution of Littorelletea uniflorae species is appreciable, are clearly associated with soft waters and their habitats are representative of the Littorelletea uniflorae class. The massive development of the phytocoenoses with both L. uniflora and M. alterniflorum in the Lobelia lakes is not always indicative of the increase in water hardness and euthrophication of waters typical of the communities of the Littorelletea uniflorae class. The M. alterniflorum dominated phytocoenoses without other Littorelletea species could be good indicators of the above processes taking place in such water ecosystems.
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Entoloma jahnii, a rare species in Europe

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The authors describe two localities of Entoloma jahnii Wölfel & Winterh., which were found during the mycocoenological research in Pomerania and Wielkopolska Regions in the phytocoenoses of Carici elongatae-Alnetum and Galio sylvatici-Carpinetum associations. The article consists of a description of gathered specimens and some remarks concerning ecology of this rare species.
Habitat studies were conducted on three rare plant communities dominated by Nuphar pumila, Nymphaea candida and Hydrilla verticillata in lakes of north-eastern Poland. The comparison of habitat properties of these three types of phytocoenoses with those of Nuphar lutea common in the area under study was also performed. It was demonstrated that the plant communities studied were ecologically distinct. The habitats of the phytocoenoses of N. pumila differed most significantly from those of the other phytocoenoses. They often inhabited softer waters poor in Mg2+, dissolved SiO2, but rich in total Fe, PO43−, NO3−, and were associated with acidic substrates containing lower levels of Ca2+ and Na+, but greater amounts of total Fe and NO3−. The differences in the habitats of H. verticillata and N. candida phytocoenoses were most pronounced in the case of four properties of water: Na+, K+, Cl−, and Mg+. Their values were lower in waters of the H. verticillata phytocoenoses. The habitats of all the three types of rare phytocoenoses differed considerably from those of N. lutea. The most significant differences were found between the N. lutea and N. pumila phytocoenoses and the smallest differences were between the patches of N. lutea and N. candida. The properties of water were more important in differentiating the habitats of the phytocoenoses studied than the substrate properties. Due to alkalization and increase in water hardness in the lakes studied the stands of N. pumila are among the most threatened. The patches of N. candida and H. verticillata, which occur in waters with a wider range of hardness and tolerating a slight increase in trophy, can still continue to persist in the lakes for a long time.
In the summer seasons of the years 1996-1998 habitat studies of 60 phytocoenoses of Phragmitetum communis in 30 lakes of Wielkopolska region were carried out. The aim of the study was a comparison of two groups of phytocoenoses exposed to different effects of wind (and waves) and two other groups subjected to a different degree of anthropopressure in respect to 28 properties of water and 23 properties of substrate. Results were expected to answer the question whether the phytocoenoses of this community reveal an internal ecological variability (habitat and floristic) in the local scale as well as to determine which of the two factors has a more important differentiating effect on the phytocoenoses and their habitats.
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