Abstract

Biological invasions represent one of the most serious global environmental threats. One of their negative aspects is a biodiversity loss in the natural ecosystems. Our study reports the results of the evaluation of changes in the proportion of invasive alien species and the results of the evaluation of the changes of the diversity in various types of forest, grassland and ruderal vegetation of Bratislava city over the time. In total, 26 invasive alien taxa were recorded in the vegetation of Bratislava. The majority of invasive taxa were recorded in both time periods. Five invasive species (Echinocystis lobata, Fallopia japonica, Helianthus tuberosus, Juncus tenuis, and Solidago canadensis) were recorded only in the more recent period. Most of the invasive species prefer ruderal habitats, and some of them also invade the forest vegetation (mainly the floodplain forests). In the dry grasslands of the class Festuco-Brometea, no invasive species were recorded in both periods. The statistical analysis revealed the increase of the average percentual number of invasive alien species in the majority of classes of the forest and ruderal vegetation of Bratislava over the time. In the majority of classes, where the proportion of invasive species increased, the Shannon–Wiener index of diversity of all species decreased significantly over the time. Our results contribute to the knowledge about biological invasions in cities.

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