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Abstract
Pollen-mediated gene flow is one of the
main concerns associated with the introduction of
genetically modified (GM) crops, since growers of GM
varieties normally do not take into account its possible
impact on conventional and organic growers therefore
generating negative externalities. Should a premium
for non-GM varieties emerge on the market,
'contamination' with GM pollen would generate a
revenue loss for growers of non-GM varieties. The
existence of such externalities has led the European
Union (EU) to put forward the concept of coexistence
in order to guarantee farmers' freedom to plant both
conventional and GM varieties without generating
economic losses to conventional farmers. The first
part of this paper develops a simple economic model
analysing the problem of pollen-mediated gene flow as
a particular kind of production externality. The
model, although simple, provides useful insights into
the policy needed to regulate coexistence.
Since pollen-mediated gene flow is distance-dependent,
the externalities will depend on the spatial
structure of GM adoption in the landscape. The
second part of the paper, taking GM herbicide
tolerant oilseed rape (Brassica napus) as a model crop,
uses a Monte Carlo experiment to generate data and
then estimate the effect of some important policy
variables (i.e. number of GM and conventional fields
in the landscape, width of buffer zones and spatial
aggregation) on the magnitude of the externality
associated with pollen-mediated gene flow. Our results
show that buffer areas on conventional fields are more
effective than those on GM fields and that the degree
of spatial aggregation exerts the largest marginal
effect on the externality to conventional growers. The
implications of the results for the coexistence policies
in the EU are then discussed.