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Aim Taxonomic comparisons of alien floras across climatically similar regions have been proposed as a powerful approach for increasing our understanding of plant invasions across scales. However, detailed comparisons between the alien biotas of climatically similar regions are scarce. This study aims to compare the taxonomic patterns of alien species richness in mediterraneantype climate areas of central Chile and California, in order to better understand how climatically similar regions converge or diverge in terms of their alien flora.Location Central Chile and California, United States.Methods We compared the alien floras of the state of California in the United States and central Chile, considering within-region variation and taxonomic composition up to the species level. To test for within-region variation, administrative units and counties were grouped within seven latitudinal bands for each region. We tested for differences in the relative contributions of the various origins of the naturalized species to each region. We used a family naturalization index to establish which families had relatively higher numbers of naturalized species in each region. We evaluated the similarity, using cluster analyses with Jaccard's similarity index, of alien taxa between regions and latitudinal bands using presence-absence matrices at the species, genus and family levels. We used principal components analysis to determine the presence of a compositional gradient including all latitudinal bands. ResultsWe recorded 1212 alien plant species in California and 593 in central Chile, of which 491 are shared between the two regions. These figures include 25 species that are native to California and 37 that are native to Chile. A comparison between the alien floras of central Chile and California reveals three major trends: (1) higher naturalized species diversity for California than for Chile, at all taxonomic levels; (2) differences in the proportion of species according to origin, with America, Africa, Asia and Australia providing a larger number of species in California than in Chile; (3) segregation between regions in terms of taxonomic composition of their alien flora, and a rather weak differentiation within regions; and (4) a trend towards higher similarity between the alien floras of latitudinal bands associated with higher levels of human disturbances. Main conclusionsThe alien floras of central Chile and California are significantly different, but this difference diminishes in highly disturbed areas. Thus, the current high levels of species movement caused by globalization, together with increasing levels of anthropogenic disturbances, should reduce the Journal of Biogeography (J. Biogeogr.) (2008) 35, 614-624 614 www.blackwellpublishing.com/jbi ª 2007 The Authors

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RESUMENEl estado de conservación de la fl ora nativa a una escala administrativa como la regional es útil para implementar medidas que reduzcan la pérdida de biodiversidad a nivel local. En este trabajo se clasifi ca la fl ora nativa de las regiones de Arica-Parinacota y de Tarapacá según su estado de conservación, utilizando una base de datos de 7.432 registros georeferenciados que corresponden a 717 especies vasculares nativas. La clasifi cación se realizó utilizando principalmente los criterios de distribución geográfi ca de UICN (versión 3.1). Un 27,6% de las especies nativas presentes en estas regiones presentan problemas de conservación (3,2% En Peligro y 24,4% Vulnerable). En la Región de Arica y Parinacota las especies amenazadas alcanzarían el 34,4% de la fl ora nativa y el 24,3% en la Región de Tarapacá. La fl ora nativa de estas dos regiones tiene un grado de amenaza mayor que los encontrados en las regiones de Antofagasta, Atacama o Coquimbo. Esto se explica parcialmente por distribuciones restringidas (bajas extensiones de la presencia y/o áreas de ocupación) sumado a una disminución en la calidad de su hábitat. PALABRAS CLAVE:Categorías de conservación, especies amenazadas, plantas nativas, Desierto de Atacama, Altiplano. ABSTRACTKnowledge of the conservation status of the native fl ora at an administrative level, such as the regional level, is useful to take actions to reduce biodiversity loss at a local level. In this study, we classifi ed the native fl ora of the Arica-Parinacota and Tarapacá Regions according to its conservation status using a database of 7,432 geo-referenced records corresponding to 717 native vascular species. The classifi cation was carried out using mainly geographical criteria of IUCN (version 3.1). A 27.6% of the native species in these regions have conservation problems (3.2% Endangered and 24.4% Vulnerable). In the Arica-Parinacota and Tarapacá Regions, 34.4% and 24.3% of the species, respectively are threatened. The native fl ora of these two regions has a greater degree of threat than that found in either Antofagasta, Atacama or Coquimbo. This is partially explained by restricted distributions (extent of occurrence and/or area of occupancy) combined with a decline in habitat quality.