Small-scale circulations caused by complex terrain affect pollen deposition

We combined a high-resolution atmospheric dynamical model and a Lagrangian dispersion model to assess the influence of complex terrain (e.g., mountains and valleys) on the movement of pollen from a source of genetically modified bentgrass (Agrostis stolonifera L.). We simulated 6 d (22-27 June 2003) from a reported case where gene flow in bentgrass was observed at distances greater than 20 km near Madras, OR (44°44′24″ N, 121°9′30″ W). Our model resolves the effects of complex terrain and local turbulence on pollen dispersion that were not considered by previous studies. We simulated pollen deposition over 20 km from its source and at locations where gene flow was previously observed. Our simulations showed that local terrain strongly affected deposition; for example, pollen grains were not deposited in large quantities within valleys or on the windward sides of mountains. Examination of the flow in these regions indicated that complex terrain creates local circulations that must be considered when predicting the potential for gene flow.