Invasion trends of aquatic Ludwigia hexapetala and L. peploides subsp montevidensis (Onagraceae) in Italy based on herbarium records and global datasets

Identifying areas susceptible to invasion by an alien species is a strategy of prevention. We used national herbaria and global databases to assess the invasion trends of the two aquatic invasive species Ludwigia hexapetala and Ludwigia peploidessubsp. montevidensis in Italy. We defined the invasion status with invasions curves and predicted potentially suitable areas with Species Distribution Models based on WorldClim variables and the human footprint index. Low seasonal variation in temperature and precipitation, temperature ≥ 20 °C in the warmest, driest and wettest periods of the year and precipitation in the coldest period are the bioclimatic factors that most account for the potential distribution of the two species. The human footprint has lower relative importance than bioclimatic variables. All Italian peninsula appears as a suitable bioclimatic environment for the invasion of the two Ludwigia species, except the Alps and the highest peaks in the Apennine. Based on the current distribution of the species in Italy and the mostly densely invaded areas globally, the agricultural land surrounding the current invaded areas and along the Italian coasts is the most vulnerable to the invasion. Considering the trend of the invasion curves, which have been sharply rising for the latest decades, there are reasons to expect that the alien Ludwigia species will continue their expansion, if no timely and effective actions are taken. Informative campaigns, accurate monitoring and prompt management are fundamental preventive tools in areas predicted as vulnerable to invasion by this study.