The article presents the results of an analysis of the alien fraction of coenofloras of the classes of pioneer vegetation of Ukraine. In plant communities of the newly formed ecotopes, 113 alien species of 32 families and 88 genera were identified. A value of the general index of adventization of coenofloras of the classes of pioneer vegetation of Ukraine is 13.4%. The highest level of anthropogenization was established for the plant communities of Bidentetea, Cakiletea maritimae and Isoëto-Nanojuncetea. The leading families of the alien fraction of the studied coenofloras are Asteraceae, Brassicaceae and Poaceae. It has been revealed that terophytes prevail in the biomorphological spectrum of the alien fraction of coenofloras of the classes of pioneer vegetation in Ukraine. The ecological analysis of alien species has shown the predominance of the species with a very wide ecological plasticity in relation to all abiotic factors. It was established that in the investigated coenofloras kenophytes predominate by the time of immigration, and epecophytes – by the degree of naturalization. The analysis and comparison of species composition of the alien fractions of the typological floras of pioneer plant communities by means of Jaccard indices showed the highest similarity between the Isoëto-Nanojuncetea and Bidentetea classes, as well as Festucetea vaginatae and Helichryso-Crucianelletea maritimae. For determination of the degree of anthropogenic transformation of coenofloras of the classes of pioneer vegetation of Ukraine, the indexes of archeophytization, kenophytization, modernization and fluctuation of the flora have been calculated. It has been established that 26 species of 11 families and 25 genera are invasive. Among them, Amorpha fruticosa, Ambrosia artemisiifolia, Anisantha tectorum, Apera spica-venti, Bidens frondosa, Centaurea diffusa, Conyza canadensis, Echinocystis lobata, Elaeagnus angustifolia, Impatiens glandulifera, Solidago canadensis and Phalacroloma annuum are transformers, which constitute the greatest threat to pioneer vegetation due to their diverse impacts.
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