Recommendation 3. The framework used by USDA to evaluate imported plants for potential release as forage, crops, soil reclamation, and ornamental landscaping should be expanded to include rapid multitiered evaluation of the hazards that these species might pose. Controlled experimental field screening for potentially invasive species should be pursued for species whose features are associated with establishment and rapid spread without cultivation and whose immigration history is unknown. Similar efforts to acquire life-history and population data in situations that approximate field settings would be beneficial in the case of nonindigenous insects and pathogens of concern, including species proposed for deliberate introduction.
A species’ performance in environments it has not encountered before can be quantified only through experimentation (Hairston 1989, Mack 1996a). The paucity of our knowledge of the early stages of an invasion demonstrates the need for experimentation based on carefully constructed hypotheses about a species in specific ranges under measured environmental conditions.
A geographically broad network of experimental gardens should be established to identify species that could readily spread and persist. In addition to averting the release of a potentially invasive species, results of field trials would substantially enhance the ability to detect common patterns of plant performance in new environments. Extending those ideas to insects and pathogens, including those under consideration for deliberate introduction, would be valuable, although practical considerations associated with experiments in field settings may be more difficult to overcome.
Recommendation 4. Information on invasions by plants and plant pests around the world should be assembled and updated regularly. Explicit information on new invasions in the United States—such as description of new locales, the partitioning of the species’ genetic variation, and epidemiology of its spread—should be gathered and communicated more effectively to the scientific community; this information is essential in continually revising expert judgment. Careful recording of the circumstances of arrival, persistence, and invasion of nonindigenous species in the United States would substantially improve prediction and risk assessment.
First detection of the escape of a potentially harmful nonindigenous species in the United States and the rapid communication of this discovery among investigators, APHIS, land managers, and others interested in nonindigenous species are neither certain nor routine. Reporting of first detection is often restricted to informal alerts to subscribers on e-mail lists, and the reported information that is reported varies widely in completeness. If a high-profile invasive species, such as the Asian long-horned beetle or the zebra mussel, is detected, there may be an