Invasive species: vectors and management strategies

Every time I met Ewald Weber over the last few years, he said he was working on ‘the book’. Only when I saw it published could I understand why it took so long — the amount of information he has synthesized is breathtaking. The book is, by far, the most complete overview of invasive plant species globally and, even better, the information is amazingly well organized. The introduction is pragmatically brief, outlining basic principles of the invasion biology of plants, commenting on practical aspects such as impact and control strategies, and explaining the scope of the book and its organization. Useful references to important web sites and important general papers are not missing either. In some cases, Weber’s approach to terminology differs from mine (e.g. that a plant can become invasive within its native range), but this is a relatively minor issue. The core of the book comprises species accounts in alphabetical order, each given a single page with most important synonyms, information on life form, commercial use (i.e. planting purpose), invaded habitats, brief description and succinct paragraph on ecology in both native and introduced geographical range, and reference numbers that relate to a list at the end of the book. Last, but not least, is information on the geographical distribution of species. The way the information is organized here is simply superb. The world is divided into nine regions (Fig. 1), each divided into subregions (32 in total); most of them are within political boundaries, hence clearly circumscribed. This approach made it possible to delimit each species’ distribution in each subregion as to whether it is native, naturalized outside natural areas (termed ‘introduced’), or invasive in natural areas. An important issue that needs comment is the species coverage, since the terminology differs from that recently suggested in the literature (Richardson et al ., 2000; Py s ek et al ., 2004). First, Weber follows the definition of the World Conservation Union (IUCN) in considering invasive species as only those that become ‘. established in natural or seminatural ecosystems or habitats, is an agent of change, and threatens native biological diversity’ (McNeely, 2001). Invasive species in agroecosystems are explicitly excluded. Translated to the above mentioned terminology, this is an overview of invasive plant species in natural habitats. This must be borne in mind when interpreting what the data in the book tell us. Secondly, it appears that despite the author repeatedly stating that the species included represent a sample, and Hal Mooney in the introductory note pointing out that Ewald no doubt struggled over which species to include, the overview seems pretty complete to me. Although some important invaders of natural areas are not covered (e.g., Ageratum conyzoides , Agrostis avenacea , Duranta repens , Melinis repens , Opuntia vulgaris , Pseudotsuga menziesii , Senna siamea , S. spectabilis , Spartium junceum , Tridax procumbens ) and the mistake that Cronk & Fuller (2001) made by including Swietenia macrophylla is repeated (see Rejmánek, 2002), the sample of species in Weber’s book is highly representative. To my mind, the 448 species that are invasive