Abstract
The first recordings of flora and vegetation in the surroundings of the Moszne lake (Polesie National Park) started from 1960. In 1980s the water conditions in this area changed and affected the organisms that lived there. The aim of this research was to recognize the present state and changes that occurred within flora and vegetation in the course of 18 years (1995–2013). In 2013, at the beginning of June, 34 phytosociological relevés were made on the floating mat that surrounds the Moszne lake in the same locations as they were done in 1995. The obtained data was collated with figures from the literature by comparing the frequency of plant species and plant communities, average plant species coverage and by calculating Sørensen indexes. The results showed that almost the same plant communities were identified in both terms of research. It was found that 35% of the plant species had disappeared after 18 years and that the biggest increase in percentage coverage was noted in case of Phragmites australis and Sphagnum fallax. Those findings show that it is very difficult and sometimes even impossible to reverse the negative influence of water condition change on bogs.