Distribution of non-native wetland plants is facilitated by urbanization and roads in the Chicago region

Human modification of the landscape, including urbanization and road construction, has facilitated the spread and establishment of non-native plant species. Urban areas have often been introduction points for species and have a combination of factors making them susceptible to invasion; including reduced habitat area, loss of unique habitat types, and increased nutrient run-off. Roads facilitate the spread of non-native plant species by providing locally disturbed habitat and a corridor for propagule dispersal. I conducted two analyses to assess how changes in the environment through urbanization and road construction facilitate the distribution of non-native plant species. For these analyses I used species occurrence data from over 2000 wetlands within the Chicago region. In the first analysis I examined the influence of urbanization and roads on the occurrences of 15 non-native plant species. I found that species, or groups of species, responded differently to the effects of urbanization and roads. For example, occurrences of halophyte species were best predicted by road variables; halophytes were more commonly associated with major roads such as interstates and federal highways, road types that are likely to receive greater applications of de-icing salts. For the second analysis I examined non-native species composition and identified non-native-dominated community types; I then conducted a similarity-based analysis to show that these novel communities are repeated across the landscape in a predictable way. I evaluated the contribution of surrounding land cover, roads, and geographic distances among wetlands to the similarity of plant communities. Non-native species were found to be widespread across the region. I found that non-native species similarity was most strongly correlated with similarity of land cover within 100 m of wetlands. This analysis was repeated for identified community types. My findings that similar changes to the landscape have resulted in similar combinations of non-native species is evidence that anthropogenic drivers are creating novel habitats and ultimately novel community types. Together my analyses have implications for understanding and managing non-native plant species within urban areas