Disturbance corridors, such as roadways, have been identified as a primary means by which non-native species have spread throughout the United States. Recent research has investigated the relationship between varying levels of disturbance and corridor vegetation within select regions, but has failed to make large-scale comparisons between distributions of non-native plants along roadways. This study identified common non-native and native species along interstates and two-lane roadways in nationally protected areas throughout the north central and western states. Roadside vegetation was sampled every other mile in 100 mile interstate transects and every tenth of a mile in 10 mile two-lane roadway transects using presence/absence data. For each transect, species frequency was calculated and analyzed using a Principle Components Analysis (PCA). Comparisons of non-native and native species for all transects sampled showed significant differences in vegetation composition between interstates and nationally protected areas, indicating roadway type as a significant determinant of roadway vegetation. However, when comparing grassland transects, the PCA showed no significant differences in vegetation between roadway types, suggesting that interstate and two-lane roadways have similar vegetation impacts on a regional scale. Further analyses of roadway vegetation on a regional scale are needed to resolve inconsistencies between these findings.

Key words: exotics, invasive, non-native plants, roadsides