Effects of Alien Plants on Native Ecosystems*

Invasions by alien plants can change the large-scale functioning of native ecosystems and alter the population dynamics and community structure of native species. Such ecosystem-level changes affect the ways local systems interact with surrounding ecosystems, with downstream ecosystems and groundwater, and with the atmosphere. Large-scale changes in ecosystems caused by biological invasions represent a specific and convincing demonstration that the characteristics of individual species are important at the ecosystem level, and studies of biological invasions thus offer the possibility of integrating the approaches employed by physiological, population, community, and ecosystem-level ecology. The evidence that alien animals alter native ecosystems is strong, and such effects are widespread. A few examples of the effects of alien plants are equally strong, but much of the evidence for ecosystem-level effects of plants is anecdotal. Hard evidence for the system-level effects of biological invasions may help to build support for control of invasions, target resources to the most important species, and address concerns as far afield as the ecological consequences of releasing recombinant ("genetically engineered") organisms.