Native and non-native perennial Asteraceae respond similarly to land degredation in a transplant experiment

Background/Question/Methods

Previous research has reported that the herbaceous floras of post-industrial sites are often dominated by species introduced from Europe and that urban areas often have the highest numbers of non-native plants. I hypothesize that non-native species are pre-adapted to brownfield conditions due to a much longer association with anthropogenic activities than their native North American counterparts. Vegetation surveys of brownfield and old-field sites showed similar numbers of native species in both site types, but higher percent cover of native species in old fields, suggesting that the native species are present in brownfields but their growth is limited more so than that of the non-natives. To investigate this question, I transplanted one native and two non-native perennial Asteraceae species between one old field and two brownfield sites. Native Solidago canadensis was sourced from one old field and one brownfield, non-native Centaurea stoebe was sourced from one old field, and non-native Artemisia vulgaris was sourced from two brownfields. Each source population was transplanted into all three sites, with ten individuals in each site, for a total of 150 transplants. At the end of the growing season, these transplants were measured for height and number of inflorescences. 

Results/Conclusions

All three species achieved greatest height in the old field. In the brownfield sites, they reached lower heights, but all did the worst in the same brownfield site. Although these trends were the same for all species, the differences in average height were smaller for Artemisia v. The difference in average height for Artemisia v. from best to worst site was only 6.6 cm, while the differences for Solidago c. and Centaurea s. were 26.0 and 27.5 cm. This result suggests that Artemisia v. would grow best in less degraded habitat, but is less negatively affected by brownfield conditions. The source site type also mattered. The average height of Solidago c. sourced from the old field was higher (p-val=0.092). The survival rate of Solidago c. was lower for plants sourced from a brownfield when growing in a brownfield, but there was no difference when planted in an old field. These results show all three species grow better in less degraded habitat, but some non-native species are less negatively affected by brownfield conditions. The dominance of these non-natives in urban and brownfield sites is likely due to a release from competition.