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J. Touza, K. Dehnen-Schmutz, and G. Jones
predict, for example, which species will establish in new environments, start
to spread, and what sort of impacts they will have (Williamson 2001; Andersen
et al. 2004). Table 20.1 offers an overview of the studies reviewed in this
chapter.
20.2 Economic Instruments as Measures
for Preventing Invasions
In economics, invasions are externalities because they occur from the failure
of markets or regulatory institutions to account for all damages the invasive
species may cause to society (Perrings et al. 2000).An externality occurs when
the decisions of one agent have an impact on the welfare or profit of another
agent(s) in an unintended way, and when neither compensation nor payment
is made by the generator of the impact to the affected party (Perman et al.
2003). This means that the market prices of potential IAS, or of species acting
as host for pest/pathogens, do not reflect societal preferences about avoiding
the costs of invasion. In the absence of instruments to correct the externality,
responsibility for protection against IAS lies with national governments and
their prevention programmes, which can include a set of regulatory measures
(black and white lists, inspections, quarantine, etc.) which are conventionally
applied to prevent/lower the risk of invasions. The regulator also has the
option of applying economic instruments (taxes, tradable permits, etc.) as
management tools which are coherent with the “Polluters Pay Principle”, to
try to guarantee the optimal level of prevention. These instruments directly
address the effects of invasion-externalities because they confront those causing
the problem with the social costs of their activities. So far, few economic
studies have considered the use of such economic instruments to reduce the
risk of invasions. The economic instruments explored here are risk-related
taxes (at a national level), risk-related import tariffs (at an international
level), and tradable permits.
20.2.1 Risk-Related Taxes
At a national level, Knowler and Barbier (2005) consider the possible use of
taxes in the horticultural market. These authors model the horticulture industry
as a source and pathway for the deliberate introduction of potential invasive
plants. They recognise that the commercial sale of non-native plants
implies a risk that invasions may occur but that they also provide benefits for
the nursery industry and for consumers. The risk of invasion is assumed to
depend on the characteristics of the plants and on the number of nurseries
selling the plants. Therefore, the calculation of the socially optimal number of