Species introductions result in enormous economic and environmental costs. However, despite over a century of research, very little consensus has been achieved regarding particular mechanisms involved in the spread of introduced organisms. We conducted an analysis of 947 nonindigenous plants to examine the relative importance of residence time, availability of potential habitat, and biological traits on county-level distribution in Michigan.

Results/Conclusions

We found the time since introduction explained a large amount of variation in distribution. In general, plant species with distributions larger than those predicted by time alone were considered weeds by state and local authorities, while those with smaller distributions were not. We found no relationship between the type of habitat required by a plant, as estimated by coefficient of wetness, and the extent of the plant’s distribution, indicating habitat availability may not limit spread in this system. Finally, we found that pollination and dispersal systems are associated with relatively high rates of spread in some species. Through this work we will develop an improved understanding of the mechanisms that facilitate persistence and spread of nonindigenous plants, and the long-term impacts of our research are more robust guidelines for inclusion of species on watch lists.