Developing rational policies regarding coexistence of genetically-modified and conventional crops that are open pollinated requires reliable information about pollen dispersal, particularly where such crops are grown on and around mountainous terrains.  The wind flow patterns over mountainous islands are particularly complex and include land-sea breezes and slope flows that can differ substantially from the mean wind flow.   Failure to consider such local effects on atmospheric turbulence leads to misleading predictions of pollen dispersal from isolated source fields. We combined a high-resolution atmospheric dynamical model with a Lagrangian dispersion model to create a framework for predicting pollen dispersion in this complex environment.  Atmospheric modeling results confirm that such complex terrains can create land-sea airflow patterns opposite to the mean wind.  Dispersion patterns for pollen grains having diameters of 20 to100 microns from various terrain locations on a mountainous island are presented to demonstrate how pollen dispersion can vary with species and local topography. Prior knowledge of potential dispersion patterns could be instrumental in determining isolation location and distances between GM and non-GM crops on mountainous island terrains.