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Cannabis pollen dispersal across the United States

For the recently legalized US hemp industry (Cannabis sativa), cross-pollination between neighboring fields has become a significant challenge, leading to contaminated seeds, reduced oil yields, and in some cases, mandated crop destruction. As a step towards assessing hemp cross-pollination risk, this study characterizes the seasonal and spatial patterns in windborne hemp pollen dispersal spanning the conterminous United States (CONUS). By leveraging meteorological data obtained through mesoscale model simulations, we have driven Lagrangian Stochastic models to simulate wind-borne hemp pollen dispersion across CONUS on a county-by-county basis for five months from July to November, encompassing the potential flowering season for industrial hemp. Our findings reveal that pollen deposition rates escalate from summer to autumn due to the reduction in convective activity during daytime and the increase in wind shear at night as the season progresses. We find diurnal variations in pollen dispersion: nighttime conditions favor deposition in proximity to the source, while daytime conditions facilitate broader dispersal albeit with reduced deposition rates. These shifting weather patterns give rise to specific regions of CONUS more vulnerable to hemp cross-pollination.

This high-resolution meteorological dataset, developed by the U.S. Environmental Protection Agency to support modeling applications, comprises an hourly time series of weather conditions on a 12 km-square horizontal grid and has been extensively validated 24. Median dispersal kernels for each month during ( a) daytime and ( b) nighttime, separated by US climate region: Northeast (NE), Upper Midwest (UM), Ohio Valley (OV), Southeast (SE), Northern Rockies and Plains (NRP), South (S), Southwest (SW), Northwest (NW), and West (W). Adams-Groom, B., Skjøth, C. A., Baker, M. & Welch, T. E. Modelled and observed surface soil pollen deposition distance curves for isolated trees of Carpinus betulus, Cedrus atlantica, Juglans nigra and Platanus acerifolia.

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