Exotic vegetation types in urban areas are linked to longitude

Colonial Williamsburg, VA

It seems that the fruit does not fall far from the tree. In a paper published in Urban Habitats (Vol. 1, no. 1), researchers Steven Clements and Gerry Moore studied 8 U.S. eastern cities and compared the diversity of both native and non-native plants. Looking at Boston, New York, Philadelphia, Washington, D.C., Detroit, Chicago, Minneapolis, and St. Louis, they found that these cities averaged 65% native trees to 35% exotics. For the native trees, they found similar clusters of species in the Boston, New York, Philadelphia, and Washington, D.C. area; and another cluster around Detroit, Chicago and Minneapolis. For the non-native trees, they found the most similarity around Chicago and Detroit, and New York and Philadelphia. Clements and Moore surmise that the exotic tree clustering is longitudinal, and "most likely the result of the history of plant introduction in North America." The eastern seaports have the most non-native species which declines significantly as one moves westward. They also note that exotic species have more time to become established with older cities. Similar observations can be seen along the Gulf Coast near New Orleans and Mobile, though it is more latitudinal.