Interactions between fluvial geomorphology, riparian vegetation, and invasive alien woody species in the Tagliamento River, in North-Eastern Italy

Biogeomorphology, an emergence subdiscipline, recognizes the meaningful bidirectional interplay between biological communities and geomorphic processes. Changes in hydrological conditions may facilitate the establishment of plant communities, and these latter, in turn, may act as natural engineers influencing the evolution of fluvial structures. Riparian ecosystems meet several characteristics that are considered hospitable for plant growth, such as exposed sediment areas, high levels of nutrients and organic matter, and propagules availability. However, precisely these conditions along with the removal of key elements that maintain the native vegetation, may favor invasions of non-native species. Non-native vegetation can alter the dynamics and structure of the affected ecosystem causing in the worst conditions, irreparable ecological damage. Hence, it is paramount to understand the relationships between fluvial processes and vegetation and invasive alien species (IAS) in order to conduct adequate management and control. The present study aimed to assess these interactions in two sub-reaches of the Tagliamento River in the Friuli Venezia Giulia region in North-Eastern Italy. A multi-temporal analysis was conducted using datasets from 2010 and 2024, obtained from field surveys and DTMs, to evaluate the changes over time and the influence of the IAS in the study area. The results revealed that in geomorphological terms, the Tagliamento River is, as many authors have described previously, less impacted compared to other temperate rivers affected by human interventions. Regarding the vegetation in the river system, its spatial distribution follows a clear pattern with pioneer species tolerant to inundation and disturbances close to the flowing channels, and more stable tree communities growing in upper elevations under more stable conditions. Finally, from the mutual interactions between fluvial morphology and vegetation, it was stated that variables such as the elevation above the thalweg and the way it evolves may be determinants for species richness. This work attempts to highlight the relevance of research conducted addressing the interplay between these elements within the river systems. Moreover, it points out the importance of considering the role and impact of IAS to define effective management strategies for the future.