To clarify the basis of claims related to plant health, WTO, through the International Plant Protection Convention, sets international standards for phytosanitary measures in trade. Each country may establish its own standards, even if they are more conservative than the international ones, but they must be based on risk assessment and be justifiable scientifically.

The United States, as with other WTO members, is expected to benefit substantially from increased access to new markets for exports and from lower import prices for agricultural and forestry commodities. Trade liberalization in agriculture alone is expected by 2005 to raise world income by as much as $5trillion and almost double the value of U.S. exports and imports (USDA/FAS 1999). However, trade liberalization increases correspondingly the likelihood that some of the hundreds of thousands of species of plant pests not yet found in the United States will someday arrive here.

APHIS is responsible for making regulatory decisions that simultaneously facilitate trade, comply with international laws, and reduce the risk of disseminating plant pests. That responsibility is daunting; APHIS needs whatever scientific tools are available to assist regulators in meeting potentially competing objectives.


APHIS asked the National Research Council’s Board on Agriculture and Natural Resources (BANR) to review scientific knowledge about the characteristics of nonindigenous organisms, environments, and the process of invasion that could be used to refine inputs into its risk assessments, identify potential invaders, and guide the strategic allocation of its resources to safeguarding plant life in the United States.

BANR established the Committee on the Scientific Basis for Predicting the Invasive Potential of Nonindigenous Plants and Plant Pests in the United States, which comprises experts in invasive plants, plant pathology, entomology, horticulture, risk assessment, ecology, and population biology. The committee was charged to consider the available relevant historical and scientific data on plant, pathogen, and arthropod invaders and on the characteristics of plants that facilitate or impede invasions and to prepare a report that evaluates how scientific principles and procedures could be used to predict the invasive potential of nonindigenous plant pests. The committee met four times over a 12-month period, examined the scientific literature, and spoke to numerous experts on biotic invasions of agricultural and natural ecosystems.

In preparing its report, the committee undertook a four-stage analysis of the invasion process: the introduction of a nonindigenous species (immigration), its persistence at some threshold level (establishment), its proliferation and geographic spread (invasion), and finally the manifestation of its adverse effects on its new environment (impact). Chapter 2 deals with the factors that have historically influenced the accidental or intentional introduction of species into an area.

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