ABSTRACT

Since the late 1990s, the field of invasion biology has expanded in numerous ways. In 1999 President Bill Clinton signed an executive order calling for action against invasion of alien biological species in the United States, and this translated into action throughout the world. In ‘war rooms’ in the United States and elsewhere, managers strategized on how to deal with these invasive species, newly recognized for the harmful effect they may have on ecosystems (Clements and Corapi, 2005). Although Elton (1958) had first conceptualized the field much earlier, it was not until the new millennium that scientific efforts began in earnest, and many new agencies were created, often to develop cooperative efforts to manage invasive species. Weeds historically have been dealt with by agricultural agencies, but more recently the threat of invasive species was recognized by numerous other stakeholders and frequently there has been disagreement between agricultural interests and other sectors. Often it is a question of definition, and the line between agricultural weeds and invasive weeds is frequently blurred (Rejmánek, 1995; Clements et al., 2004; Smith et al., 2006; Thomas and Leeson, 2007).