The global database of invasive trees and shrubs (Richardson & Rejmánek, 2011; Diversity Distrib. 17, 788-809) has been updated, resulting in a total of 751 species (434 trees and 317 shrubs) from 90 families. Ten originally listed species were deleted (synonyms, inconclusive identification, etc.) and 139 additional invasive species (86 trees and 53 shrubs) are now included in the database. For many species, new records on their adventive distributions are added. The updated database also includes the native ranges for all listed species.
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Interest in the spread and impacts of non-native trees and shrubs on biodiversity and ecosystem functioning is accelerating (e.g., Holland-Clift et al., 2011; Keppel & Watling, 2011; Aslan et al., 2012; Brand et al., 2012; Meinhardt & Gehring, 2012; Rascher et al., 2012; Rodewald, 2012; Saure et al., 2013). This note reports on the update of our database of invasive trees and shrubs that was originally used as online supporting information for our global review of alien trees and shrubs (Richardson & Rejmánek, 2011). The database has been widely used, as shown by citations to the paper and by the volume of correspondence that we have received on a wide range of aspects of the list. As we predicted, mainly because of the lack of objective information from some regions, our initial list was incomplete. For these reasons, we feel that an update of the database should be made available to ecologists and managers. Our criteria for inclusion of species remain unchanged: the alien species should be not only naturalized (consistently reproducing), but invasive (spreading) in one or more of the 15 recognized geographical regions (for definitions see Pyšek et al., 2004). Because we deal explicitly with non-native species, cases of encroachment of native woody species (Eldridge et al., 2012) are not included in our database.
The process of updating resulted in the removal of ten of the 622 species in the original version. Some species included in the original database turned out to be synonyms for other species already listed (Cedrela toona Roxb. for Toona ciliata M. Roem., Fraxinus rotundifolia Mill. for F. angustifolia Vahl subsp. syriaca (Boiss.) Yalt., Rhamnus frangula L. for Frangula alnus Mill., Rosa eglanteria L. for R. rubiginosa L.), Acacia hockii De Wild. is native in the area where it was listed as invasive; Lonicera japonica Thunb. does not fit the definition of a shrub (it is a liana); the species status of Celtis in Southern Africa remains unresolved (C. australis/C. occidentalis); Sesbania bispinosa (Jacq.) W.Wight and Phytolacca americana L. are not woody; and Dodonea viscosa (L.) Jacq. is a cosmopolitan species (Harrington & Gadek, 2009).
On the other hand, 139 new invasive species (86 trees and 53 shrubs) were added to the database (see Appendix S1 in Supporting Information). Unfortunately, most of the new data are from previously well-covered regions and not from the regions where we believe reliable data are still missing (see below). The resulting 2013 version of the database includes 751 species (434 trees and 317 shrubs) from 90 families of angiosperms (84), gymnosperms (4) and tree ferns (2). For many species included in the original version of the database, new records on their adventive distributions were also added. Based on the current data, in terms of numbers of species, the most invaded regions are North America (212 species), Pacific Islands (208), Australia (203), Southern Africa (178), Europe (134) and Indian Ocean islands (126). Very low numbers for the Middle East (47) and Indonesia (41) may partly reflect the real situation, but the shortage of accurate information for these regions is certainly another reason. The resulting data matrix (751 × 15) is still very sparse. The majority of species (49.8%) are still reported as invasive from only one region and only 7.6% of species are recorded as invasive in six or more regions. As a substantial addition to the 2013 edition of the database, authorities for Latin names for all species are provided, and the native ranges for all species are reported (one or more of 15 recognized geographical regions). The major sources of invasive trees and shrubs are Asia, South America, Europe and Australia (each of them provided over 100 species, Asia over 200 species). A detailed analysis of species exchanges among geographical regions will be published separately.
As before, many botanists and invasion ecologists from all parts of the world contributed to this database. We thank them all. MR acknowledges support from the University of California Agricultural Experiment Station. DMR acknowledges support from the DST-NRF Centre of Excellence for Invasion Biology and the Working for Water Programme through the collaborative research project on ‘Research for Integrated Management of Invasive Alien Species’.