EPPO Global Database

EPPO Reporting Service no. 09 - 2021 Num. article: 2021/205

Impact of invasive alien plants on species composition along river banks

River systems are important corridors for the movement of nutrients and minerals, and their banks harbour a rich diversity of plant species, with many species endemic to such habitats. Such habitats are in a constant state of flux and are prone to high levels of natural disturbance which can make them vulnerable to invasion by invasive alien plants. The impacts of non-native plant species on the vegetation of a semi-natural riparian ecosystem were assessed in the Tiber River basin in Umbria (Italy). The study aimed to assess the change in riparian vegetation composition over a 22-year period by comparing data collected in 1998 at 46 sites, to data collected at 48 sites in 2020. The results showed that both datasets contained 91 species in total and there was only a 2 % increase in the number of non-native plant species (6.6 % 1998 compared to 8.8 % in 2020). However, the percentage cover of non-native species increased significantly, from 4.3 % in 1998 to 36.6 % in 2020. The three taxa that increased their cover the most were Paspalum distichum (Poaceae: EPPO List of Invasive Alien Plants), Amorpha fruticosa (Fabaceae: EPPO List of Invasive Alien Plants), and Xanthium orientale subsp. italicum (Asteraceae). Amorpha fruticosa is native to North America and was introduced into the EPPO region as a garden ornamental in the early 1700s. It can outcompete native species and has negative impacts on ecosystem services. Paspalum distichum is considered native to the Americas and is found throughout the world, including several countries in the EPPO region. The species is an aggressive invader, especially in riparian systems (e.g. Portugal) where it can have detrimental impacts on endemic vegetation. In the current study, generally, in sites where A. fruticosa is absent, P. distichum is dominant. Xanthium orientale subsp. italicum is also native to North America and is invasive in the EPPO region where it colonises disturbed habitats (roadsides, river banks and sandy beaches). All populations of the species should be monitored and controlled.


Praleskouskaya S, Venanzoni R (2021) Effects of invasive alien species on riparian vegetation over a 20-year time-lapse: a case study from the Tiber river in Central Italy. Biodiversity 22(1-2), 67-81. https://doi.org/10.1080/14888386.2021.1940277