Transportation systems cause multiple ecological impacts by altering biotic and abiotic conditions that affect ecosystem structure and functioning from local to regional scales. I am testing the hypotheses that current and future distribution of exotic species are greatly favored by transportation systems and their adjacent land (e.g., roadsides). To test my hypotheses, I first evaluated the relative contribution of different predictor variables, including roadsides and proximity to transportation systems, to explain the number and cover of exotic species in 460 study sites distributed throughout Mississippi. Then I used species distribution models (SDMs) to predict future distributions of the major invasive exotic species in southeastern United States, and to evaluate the relative contribution of the different environmental variables (including climate, topography, land cover, land use and propagule pressure) to the distribution models.
Results/Conclusions
My research of different factors that affect exotic species distributions in the southeastern United States has shown that both proximity to transportation systems and type of the closest transportation system influence the distribution of exotic plant species. I found that exotic species occurrence and abundance increased with increasing proximity to transportation systems. Transportation routes (e.g., highways and county roads) were more positively correlated with exotic species than were structurally similar utility ROWs (e.g., pipelines and electrical transmission lines). Furthermore, study sites with more than one transportation system in the surrounding landscape usually had a greater number and abundance of exotic species. This was especially significant at locations with a highway and other roads nearby, where values were three times higher than in study sites with only one adjacent highway. The results obtained from the SDMs showed that proximity to roads was one of the most important variables to predict future distributions of the major invasive species in southeastern United States. These results are similar to many published studies that indicate a positive effect of roadsides on the distribution and dispersal of exotic/weedy plant species.