Can the large ecological amplitude of Ambrosia artemisiifolia explain its invasive success in France?

In order to understand the successful spread of Ambrosia artemisiifolia in France, the variability of colonised habitat by this species was studied at 48 locations, from its central to peripheral area of distribution. Each site was characterised by a vegetation survey, a description of the A. artemisiifolia population and a soil analysis. Differences in the number of species, Shannon diversity index, evenness index and plant life form spectra were compared among the sites. A total of 276 species occurring along with A. artemisiifolia was observed. Therophytes and hemicryptophytes represented more than 80% of all the species. The two most frequent species occurring along with A. artemisiifolia were Chenopodium album and Polygonum aniculare. Multivariate analysis of vegetation surveys showed that A. artemisiifolia has a wide ecological tolerance. It colonises a large range of disturbed habitats differing in terms of vegetation cover, species composition and type of soil. The present study highlights the potential of A. artemisiifolia for invading spring crops and all seminatural or disturbed open areas. The success of its ongoing invasion can be explained by both its generalist character and the existence of vacant ecological niches, which are poorly occupied by the French native flora.