ABSTRACT
The introduction* of invasive alien plants into new ranges may have significant consequences for habitats and ecosystems. Although many invasive species have had detrimental effects on native species and ecosystems, not all invasive plants cause serious ecological harm. Many plants are unable to establish permanently, and others become naturalized into the environment, without causing any observable problems. Consequences of invasion can also be beneficial. The ‘‘tens rule’’ (Williamson 1996), stating that 10% of imported species spread, 10% of these establish, and 10% of the established species cause problems (¼ 0.1%), is generally applicable to alien plants. The challenge is to identify the 0.1% of species that can be harmful among the plant species introduced into a country or a region. If negative impacts occur, in the majority of cases these threats are causedby indirectdamage thataffects plantsprimarily throughprocesses such as competition for space and resources or alteration of ecosystem properties, for example, the alteration of soil chemistry orwater regimes. The effects and consequences of these processes, however, are often difficult to evaluate and to quantify in detail.
