6533b822fe1ef96bd127de8e

RESEARCH PRODUCT

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

subject

description

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 %) environments and degraded semi-natural (sandy grassland, dunes) environments (12 %). Western ragweed occupies the same habitats as the annual species Ambrosia artemisiifolia, but is found at the most stable sites in these habitats. Ambrosia psilostachya is highly abundant in the perennial vegetation at the start of succession (wasteland, roadsides), but is less frequent in more stressful, regularly disturbed pioneer habitats, suggesting a preference for sites with an intermediate level of disturbance. Interspecific competition may also have an effect, as suggested by its lower levels of success in communities consisting of functionally similar species thought to use the available resources in a similar manner. We found no significant impact on the structure of the plant communities occupied by A. psilostachya. However, the development of this plant in Elytrigia grasslands should be monitored and integrated pasture management, including a high plant density, should be implemented. The preliminary ecological data collected in this study should make it possible to establish a more accurate map of the risk of A. psilostachya invasion in France.