Invasive alien plant species of Union concern in the Lower Siret Floodplain Natura 2000 site (Romania)

The increasingly negative impact of invasive alien species on ecosystem structure and function, biodiversity, health, and the economy has led to an intensification of efforts to control or eradicate these species.The growing threats from invasive alien species are well illustrated by the expansion of the List of invasive alien species of Union concern (EU Regulation 1143/2014), which has been updated three times since the initial list was adopted in 2016.The number of species included has risen from 37 in 2016 to 88 today.The most recent data from Romania indicate the presence of 10 of the 41 invasive alien plant species (IAPS) of Union concern in Romania.Among them, three species (i.e., Baccharis halimifolia, Celastrus orbiculatus, and Heracleum mantegazzianum) are records submitted through citizen science apps and not confirmed through peer-reviewed publications.To provide distribution data for IAPS of Union concern in an environmentally sensitive area, between 2022 and 2023, we sampled 166 terrestrial, aquatic and riparian plots from the Lower Siret Floodplain (Eastern Romania).We identified two IAPS Union concerns, namely Ailanthus altissima in 8 (5.63%) sample areas located predominantly on the left bank of the Siret River, in the sector between Movileni and Poiana (Galati), having the primary pathways of introduction Unaided (n = 4), Release in nature (n = 2) and Transport -Stowaway (n = 2), and Elodea nuttallii in one sample area near Movileni (Galati).We recommend further monitoring, focusing on areas already invaded or likely to be invaded, as well as the removal and replacement of IAPS species.Additionally, we suggest raising public awareness through educational campaigns, increasing the use of open data repositories by scientists, as well as advocacy for a more intense use of citizen science platforms for monitoring.