Spreading of adventive plants on river banks of the Elbe River in the Czech Republic and the Danube River in Slovakia outside of harbours

摘要

In the years 1973-2004, an adventive fiora (so called neophytes) and vegetation on open river at planar level outside of harbour bodies in Bohemia on the Elbe River between the towns Melnfk and Hrensko, and in Slovakia, on the Danube River between thetowns Bratislava-Devin and Sturovo, as a part of flora and vegetation of river harbours monitoring were investigated. The banks of watercourses on open river (i.e. outside of harbours) are in direct contact with river current carrying away diasporas ofplants not only from harbours but also from all ecotopes along river in river basins. In this process, floods play a significant role as well. With regard to transport of diasporas, the Elbe River harbours, in comparison with the Danube River harbours (Bratislava, Komarno), are influenced more significantly by watercourse that is associated with a lower height of harbour embankments and walls above the level of watercourse. Spreading of plants on open river banks is influenced, apart from human activities, also by the erosion-accumulation process that has a selective impact during ecesis of introduced species. Flora of river banks is therefore less rich than flora of actual harbours. In total, there were found on the banks of both watercourses 54 (=100%) adventive plant species (not including archeophytes). The highest number of them belonged to therophytes (68%) and hemicryptophytes (22%). Of 54 neophytes on the banks of the Elbe and Danube Rivers, 50% belong to invasive species. On the Danube River,they were occasionally registered also in the vegetation of the ass. Bidenti-Polygonetum hydropiperis, Odontito-Ambrosietum artemisiifoliae and Rutnici crispi-Agrostietum stoloniferae. Of newly spreading invasive species, Xanthium saccharatum and Amaranthus blitum subsp. emarginatus var. pseudogracitis were registered on the Danube River in Slovakia. The difference in presence of alien expansive weeds is significant on both watercourses outside of harbours: 3 species on the Elbe River, 8 species on theDanube River, total 9 species that is not quite 1/3 of all these species known from the harbours. For their spreading, there are particularly favourable broad areas of the Podunajska nizina Lowland, on which fields many species of expansive weeds are naturalised that we cannot state for the planar Elbe River Lowland. To conclude, it can be noted that watercourses in cultivated landscape represent an important way of spreading of neophytes, especially of invasive species.