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Abstract
Isolation distances to limit the risk of cross-pollination from transgenic to nontransgenic
crops can severely limit the potential use of transgenic crops through a so-called
'domino effect' where a field of non-transgenic crops limits adoption of
transgenic crops not only on plots in its direct vicinity, but also in plots further away
as its neighbors are forced to grow the non-transgenic varieties, forcing their
neighbors to grow the non-transgenic variety, and so on. The extent to which this
effect takes place, however, may depend crucially on the type of farm. For example,
dairy farms can use grassland as a buffer between transgenic and conventional maize
plots.
This article assesses the effects of isolation distances for transgenic maize in
dairy farming. A spatially explicit farm model is applied to a region in the Southern
Netherlands to identify to what extent a single farmer (who uses non-transgenic
maize) can limit other farmers’ potential to grow transgenic maize. The main findings
are that 50% or more of the farms in the study area will not affect the potential
adoption of transgenic maize by growing conventional maize at all. This result even
holds under distance measures of 800m, which is the largest distance implemented by
member states of the European Union. When they do have such effects, isolation
distances can reduce the benefits from transgenic maize by €5,000 - €6,000, for a
considerable part through a domino effect. Large net benefits of transgenic maize may
limit the spatial effects as farmers are more willing to relocate maize production to
areas where transgenic maize is allowed.