Ecology and impact of an emerging invasive species in France: western ragweed (Ambrosia psilostachya DC.)

Western ragweed (Ambrosia psilostachya DC.) is a perennial member of the Asteraceae native to North America that was introduced into France at the end of the 19th Century. Field observations have provided evidence of a recent expansion and of the emergence of dense clonal populations potentially threatening the biodiversity of certain Mediterranean sensitive or degraded habitats. This study therefore aimed to identify the habitats colonized and the ecological conditions favouring successful colonization by this species, and to determine its impact on the plant communities of the semi-natural habitats invaded. Ambrosia psilostachya mostly colonizes ruderal (61 %) and cultivated (14 %) enviro…