Environmental Engineering Reference
In-Depth Information
Observability : how easy is it to detect the presence of an NIS?
Separability : how easily can importers/exporters disentangle unwanted NIS from
wanted goods and services?
Traceability : if an invasion occurs, how
fi
nely can the source of the release be pin-
pointed?
Predictability : what do policy-makers know about the growth function, physical
and economic impacts associated with individual NIS?
We use this taxonomy to build a framework for tailoring pre-emptive NIS policy. Our goal
is to assist policy-makers in identifying which instruments are best able to target NIS
damage, given the economic and ecological characteristics of the problem at hand. Along
the way, we identify areas where NIS introductions and generic trade and environment
problems overlap, and so policy-makers interested in NIS can look to general research on
trade and environment problems for solutions. We also identify research gaps, paying par-
ticular attention to research prompted by NIS problems that can inform policy on a wider
range of problems.
Trade and invasives - the causal link
Traded goods and services, as well as the vessels that deliver these traded commodities,
are a principal conduit for NIS introductions. We begin our review with the following
question: is the assumption that trade
ows drive NIS introductions borne out by the
data? This question has received relatively little empirical study.
Dalmazzone (2000) conducts a cross-country regression using as a dependent variable
the ratio of established exotics to indigenous species. She
fl
fi
nds '[n]either trade as a share
of GDP nor tourism . . . [provides] statistically signi
fi
cant explanations of vulnerability
to plant invasions' (p. 23). She does
nd, however, that merchandise imports and import
duties are positively and negatively, respectively, correlated with the exotics ratio,
although only the import duties measure is statistically signi
fi
cant.
Levine and D'Antonio (2003) examine the relationship between international trade and
NIS establishment in the USA. They construct species-import curves using historical trade
and NIS establishment data on cumulative totals beginning in 1920. Trade forecasts are used
to predict the number of new NIS expected to become established in the US between 2000
and 2020: conservative estimates predict 115 new insect species and
fi
fi
ve new plant pathogens.
erentiate NIS and trade data
on the basis of biogeographic origin. Costello et al. (2007) estimate the NIS invasion risk
posed by di
The Levine and D'Antonio (2003) analysis does not di
ff
ff
erent regions of the world to the San Francisco Bay. They
fi
nd that invasion
risk is di
erentiated by region of origin and that the number of introductions from a
region is a concave function of imports. A related literature in marine ecology establishes
a
ff
rm causal link between certain NIS pathways, ballast water carried by ships in partic-
ular, and NIS introductions; see Ruiz et al. (1997) and Holeck et al. (2004).
In sum, the few extant empirical studies suggest that NIS introductions are positively
correlated with trade. For the rest of this review, we take this as a maintained assumption.
fi
Targeting
Trade facilitates NIS introductions. Logic would suggest that any instrument reducing
import volumes would thereby reduce introductions and NIS-related damage in turn. The
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