Thomas J. Stohlgren1, Petr Pysek2, John Kartesz3, Misako Nashino3, Anibal Pauchard4, Marten Winter5, Joan Pino6, David Richardson7, John. R Wilson8, Brad Murray9, Mingyang Li10, Laura Celesti11, and Xavier Font6. (1) USGS Fort Collins Science Center, (2) Institute of Botany, Academy of Sciences, Prujonice, Czech Republic, (3) Biota of North America Program, (4) Universidad de Concepcion, IEB, (5) UFZ Helmholtz Centre for Environmental Research, (6) Autonomous University of Barcelona, (7) Stellenbosch University, (8) Center for Invasion Biology, (9) University of Technology Sydney, (10) Nanjing Forestry University, (11) Università La Sapienza
Background/Question/Methods Modern trade and transportation has re-united the continents. We evaluated the occurrence of the top 120 (top 528 in some cases) widely distributed plant species in North America (north of Mexico), Chile, Argentina, Republic of South Africa, Europe, New South Wales (Australia), and the Peoples Republic of China, by examining the numbers of regions or cells occupied in each area by native and alien species (i.e. species from other biogeographical regions). We asked how many plant species on the lists are alien (i.e., from other regions), and if alien species are as widely distributed as their native species counterparts.
Results/Conclusions
We show that at regional levels, invasive plants are often the most widely distributed plant species, but that the global patterns of invasion are highly asymmetric. Over half of the widely distributed species of the top 120 list in North America were alien. Alien plant species were also well represented on the top 120 lists for New South Wales (43.3%), Chile (34.2%), Argentina (29.7%), and the Republic of South Africa (22.5%). Europe had almost no alien species on the list. We also show how invasion patterns are affected by scale. The pattern within the United States varied by region with California having 20% alien plants species in its top 120 species list, in comparison to Florida, which had only one alien species on its top 120 list. Meanwhile, aliens (non-native species introduced after 1500 A.D.) comprised only 11.7%, 5.0%, and 4.2% of widely distributed plant species in the European regions sampled: Great Britain and Ireland, Catalonia (Spain) and the Czech Republic, respectively. The patterns of invasion in the United States, Republic of South Africa, and Europe were corroborated when a greater number of plant species was examined (n = 536 species). Only 2.1% among these most distributed species in Europe are alien, while in North America it is 40%. However, despite the disparity in the sizes of the areas evaluated, or in the number of alien species in different areas, we discovered that the alien species present were equally or more widely distributed in comparison to native species on the lists. These widespread alien species contribute to the continued homogenization of the global flora.
