Long-Distance and Dynamic Seed Dispersal from Horseweed (Conyza canadensis)

Seed dispersal has significantly contributed to horseweed invasion in ecosystems. However, there is a lack of research on long-distance (more than 1 km) and dynamic (hourly) seed movement during an entire seed-shedding season and under different atmospheric conditions. To fill this knowledge gap, the Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) model, accounting for meteorological factors and biological dynamics (hourly-order seed emission), was validated using experimental data. The validated model was run for different atmospheric conditions (wind speed and updraft-vertical turbulence) to estimate the longest distance (LD, from the source with more than 1 seed ha^-1 deposition) and distribution of seed dispersal during one day (8:00 to 18:00). In a weak wind condition (1-4 m s^-1 at 10 m height, standard deviation of vertical wind velocity = 0.5-0.6 m s^-1), LD was about 36.5 km, and 4% of seeds were deposited farther than 5 km. In a strong wind condition (5-7 m s^-1, 0.8-1 m s^-1), LD was 165 km, and 27% were blown farther than 5 km. At the end of the seed-shedding season (44 days), seed dispersal exceeded 186 km; 79% were found within 5 km and 14% were blown farther than 10 km.