persal and spread were prolific seed production; reproduction by corms; dispersal by wind, water, machinery, animals, and humans; and the ability of seeds and corms to tolerate some stress. The third criterion was an economic-impact rating that was based on potential reduced crop yield, lower commodity values, and possible loss of markets. The impact was rated as high on the basis of the potential economic loss from stock poisoning and reduced crop yield. The fourth criterion was environmental impact, which was also scored as high on the basis of potential impact on community structure and human health and the impact of control practices. The total score for the consequences assessment was 12, leading to an overall rating of high consequences (score of 3). The final measure of risk was based on the sum of the score for risk of establishment (3) and the score for consequences (3). That sum led to an overall evaluation of high risk.

exposure pathway-response relationships and did not focus on only one part or one pathway.

The advantage of a scenario system is that it captures the ecological context, as recommended in present ecological risk assessment (Suter 1993, USEPA 1998). All the information is used, and a line of evidence is set aside only after compelling evidence warrants that action. The greatest limitations are that the analysis can be data-intensive and still remain blind to novel and unknown conditions. Modeling and use of related data can overcome some problems related to missing data, and peer review might be able to address some of the issues related to unknown conditions.



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