Gene flow is managed using isolation distances, which are set using qualitative risk assessments by experts.
Increasing isolation distances led to reductions in pathogen population and yield loss only in the strategy of WOSR-isolation.
Our findings argue for incorporating a certain degree of flexibility into SEACERs by advising pollen barrier agreements between farmers rather than imposing rigid isolation distances on GM farmers.
These measures usually include the setup of large and fixed isolation distances, pollen barriers, flowering coincidence, crop rotation and other measures, which are very hard to fulfill in a multi-field setting.
Rigid rules, such as the requirement of large isolation distances everywhere, may raise the cost of coexistence measures, particularly in densely planted areas, without necessarily meeting the objectives of the European Commission.
Field experiments on GM cottons in eastern Australia were commonplace, but even there, regulators required confirmation that the containment practices already in place (buffer zones and isolation distances) were effective.
Our empirical findings led us to advance the proposition that flexible SEACERs based on pollen barriers are more likely to respect the proportionality condition than rigid SEACERs based on isolation distances.
We could show that particularly the current primary OSR cropping regions are largely unsuitable for coexistence and would suffer from a net loss of OSR area even at isolation distances of 400 or 800 m.
Determination of isolation distances to ensure harvest purity should thus consider past history of OSR cultivation in the area and, in particular, how current or future cropping systems will manage volunteers.
Isolation distances usually disregard landscape specifics.
Isolation distances from field neighbours were calculated using computer programs written in SIMULA [30].
