Recent Advances in Understanding Plant Invasions

Abstract

In the last two decades biological invasions have drawn increasing attention (see e.g., Drake et al. 1989; Lodge 1993; Williamson 1996; Lonsdale 1999; Alpert et al. 2000; Kolar and Lodge 2001). Compared to other subjects of ecological investigation, studies related to biological invasions have almost exploded in number during the last years (Fig. 1). Increase in the number of published papers on invasive plants between 1990 and 2002 (filled circles, plotted against the left y-axis). The data were obtained by a year-specific search in the ISI WebOfScience database using invasive plant(s) orplant invasion(s) as search terms (for the title and the abstract). Note that not all papers on plant invasions were retrieved by these search terms, nor are papers on other invasive organisms included. To account for the constantly increasing journal coverage by ISI, the development in the number of invasionrelated studies is shown calibrated against the development in the number of ecology-related studies in the same period of time (open squares, plotted against the right y-axis). While the number of ecology-related studies increased fairly linearly there has been an exponential increase in the number of studies related to invasive plants in the last years The fact that an increasing number of ecologists gets caught up in the problem of biological invasions can be attributed to several reasons. First, biological invasions are increasingly recognized as one of the most important threats to biodiversity (D’Antonio and Vitousek 1992; Vitousek et al. 1997a; Walker and Steffen 1997; Mooney 1999), i.e. biological invasions tend to homogenize the earth’s biota (Lodge 1993; Vitousek et al. 1997b; Mooney 1999; Mack et al. 2000). Second, biological invasions can also pose severe environmental, economic and sometimes even health threats (Vitousek et al. 1997a,b; Mack et al. 2000 and references therein, Pimentel et al. 2000). Invasive species affect native species and ecosystems by competing directly for resources that native species require, by altering ecosystem functions and processes such as nutrient and hydrologic cycles, and fire frequency and/or intensity. There are virtually no natural areas left that have not felt the impact of non-native invaders (Usher 1988). Third, biological invasions represent great natural experiments for the ecologist whose investigation is extremely valuable for the understanding of population spread (Sakai et al. 2001) and community- and landscape-level processes affecting the patterns and abundance of species at large spatial and temporal scales, i.e. scales which are otherwise hardly accessible for experimental ecologists.KeywordsInvasive SpeciesPlant InvasionBiological InvasionAlien PlantPropagule PressureThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.