Coexistence of GM and non-GM crops with endogenously determined separation

The possibility that genetically modified (GM) crops may contaminate non-GM crops through pollen-mediated gene flow presents a challenge to coexistence of GM agriculture with conventional and organic farming systems. In this paper an analytical model of coexistence is developed that allows for endogenous derivation of efficient widths and allocation of pollen barriers to limit contamination of non-GM crops. To reflect the uncertainty that surrounds pollen dispersal mechanisms the model contains a stochastic contamination function and safety rule decision mechanism, constraining the level of contamination to remain below a tolerated adventitious presence with a given probability. Two policies are considered and their performance is tested: the tolerance level of adventitious presence, and the allocation of responsibility for implementing coexistence measures to either GM or non-GM farmers. The relative size of GM rents (the value of productivity gains and the non-pecuniary benefits from GM crops), rents for identity preserved non-GM crops (price premiums realised over the GM crop price), characteristics of farms, and possible variation in agricultural landscapes are also taken into account. The findings indicate that conventional adventitious presence tolerances can be met without ex ante mandating large widths of pollen barriers. At the policy level, the findings of this paper are relevant for setting region-specific pollen barriers widths, and/or for establishing institutions that facilitate cooperative coexistence.