As Bethany explains, the paper compares the spatial distributions of invasive vs. native plants across the US. Although we commonly think of invaders as starting at one unlucky spot and moving outward, our research found that invasive plants are incredibly widespread – even the relatively rare ones. In contrast, native plants do not receive the advantage of widespread human introduction. We’re actively assisting the migration of invasives and leaving behind the natives.
You can read more about the work here and here http://www.umass.edu/newsoffice/article/non-native-plants-us-widespread-and-plenty