The level of invasion by alien plants in the Ploučnice River basin

The level of invasion varies according to the habitat type. The aim of this paper is to evaluate the level of invasion in the basin of the Ploučnice River in North Bohemia. The values of the level of invasion were quantified for vegetation plots from the Czech National Phytosociological Database and for segments of riverbank vegetation which were mapped at own field research. Ten maps showing the level of invasion by alien plants were developed based on a quantitative assessment of the level of invasion of particular habitat types at different altitudes. The levels of invasion were measured as proportion of the species that are aliens and total cover of alien species, the same was done for archeophytes and neophytes separately. The other option to quantify the level of invasion was using levels of count of invasive neophytes in the riverbank vegetation. Within each habitat the level of invasion was related to altitude. If the relation was significant, the level of invasion in that habitat was extrapolated according to that relation to altitude. Mean levels of invasion were used for the habitats which the relation was non-significant for. The west, northeast and the central parts of the assessed basin were evaluated as the most invaded areas. It is caused by the occurrence of the most invaded..