Differences in invasibility of two contrasting habitats and invasiveness of two mugwort Artemisia vulgaris populations.
The establishment success of non-native invasive species is often attributable either to habitat invasibility or inherent species traits. In this study, the interplay between these two factors in the establishment, expansion and plasticity in growth of the clonally reproducing invasive weed mugwort Artemisia vulgaris in two contrasting habitats, as well as the potential management practice of monthly mowing, were explored. The resource allocation patterns and spatial distribution of ramets originating from two naturalized populations found in New York, USA, were investigated over a 3-year (2001-03) period. Ramets from these morphologically distinct populations were transplanted into each of two contrasting habitats to determine the invasive potential of these populations and the relative resistance of each habitat to invasion. Total ramet production, average ramet height and spatial distribution patterns differed significantly between the two populations, but the degree of variation in the response was habitat-dependent. There were no interpopulation differences in total biomass production. Plastic responses in resource allocation patterns, spatial distribution of ramets and relative growth rates were observed, demonstrating differences in invasive potential between the two mugwort populations. The two habitats differed in invasibility. This could have been the result of differences in community structure, competition for available resources, disturbance and/or invader traits. In addition, monthly defoliation (mowing) reduced mugwort ramet production by as much as 90% and as little as 10%. This study demonstrates that variation exists in habitat invasibility, and that intraspecific variation in growth patterns occurs in mugwort. The interaction between habitat traits and species characteristics was important in determining invasion success. The monthly mowing following the introduction of mugwort can substantially decrease the rate of spread of this clonal species, which may provide an effective management opportunity both for this species and for other clonal invaders.