For plants, abscission is the first step in the dispersal process.  Seed release is potentially affected by a large number of environmental factors, which in turn will affect dispersal patterns.  From field observations of two species of invasive thistles, Carduus nutans and C. acanthoides, we hypothesized that precipitation, temperature, and drying time strongly affect seed release.  To examine this hypothesis, flower heads were stored at three temperatures (10°C, 23°C, 27.5°C) and then tested in a wind tunnel for 1 minute at 6 m/s either immediately after collection or after one or two days of drying.

Results/Conclusions

Analysis of preliminary data shows significant effects of drying temperature on seed release.  There were also significant effects of weather events before flower heads were collected; in particular effects of prior experience of precipitation and humidity in the field.  Additionally, there was a significant interaction between drying duration and temperature treatment.  We relate these results to corresponding studies we have conducted in the field to better understand factors that affect seed release in natural settings.