Deliberate and unintentional introduction of invasive weeds: A case study of the alien flora of Ukraine

Based on the analysis of invasions of alien plants in Ukraine, the impact of non-native plant species upon the native flora and adverse consequences of their spread are assessed. A case study gives examples of the role of alien plants in fragmentation of populations of native species; contamination of genetic resources of rare and endangered native species, formation of new ecotypes and hybridization with native taxa, disruption of the structure of natural plant communities as a result of introduction of alien species and formation of specific plant communities with domination of aliens. Arguments are provided against uncontrolled casual introductions and subsequent escape from cultivation as a result of ill-judged deliberate introduction of plants for ornamental, agricultural, technical, forestry, and other uses without any preliminary assessment of their invasion potential in the region concerned. Invasions of alien plants promote dramatic changes in the taxonomic, geographical, and ecological patterns of local floras, disruptions in the phytosociological spectrum, spectra of biomorphs, deterioration of zonal peculiarities of the flora, and finally lead to the decline of the vegetation productivity. A list of highly invasive plant species threatening forest, steppe, and submediterranean zones of East Europe is provided.