Invasive plant species in urban and suburban habitats of the city of Zagreb

Urban ecosystems often form a mosaic of anthropogenic and natural vegetation. Although their naturalness is frequently disrupted by human activities, they are characterized by increased species richness due to the presence of alien flora, which most commonly spreads via transport corridors and often becomes invasive in newly colonized ecosystems. Despite the fact that invasive flora in urban ecosystems remains insufficiently studied in cities of northeastern Europe and Croatia, previous research indicates a high occurrence of invasive species. In this study, a total of 16 invasive plant species were recorded at four selected urban and suburban sites within the city of Zagreb. The family Asteraceae was the most represented, while the majority of the recorded species (69%) originated from the Americas. Hemicryptophytes and therophytes were the dominant life forms. Ambrosia artemisiifolia L. and Solidago gigantea Aiton were recorded at all sites, whereas Ailanthus altissima (Mill.) Swingle, Amaranthus retroflexus L., Bidens frondosa L., Conyza bonariensis (L.) Cronquist and Reynoutria japonica Houtt. were found at only one site, indicating differences in floristic composition between urban and suburban ecosystems.