Many plant populations fluctuate between years of high and low seed production. These fluctuations, often called mast-seeding, have typically been attributed to fluctuations in resource availability.

Recent theoretical models show that mast-seeding could also be due to the dynamics of resource allocation within individuals, synchronized among individuals by pollen limitation in low flowering years. This "pollen coupling" mechanism appears to explain synchronous, alternate-year flowering in a perennial wildflower, Astragalus scaphoides. Our past research shows that plants are more pollen limited in low-flowering years, and that pollen coupling models fit to data for this species predict alternate-year flowering in the absence of environmental forcing. Here, we present tests of two additional components of pollen coupling. First, we directly tested whether preventing fruit set caused plants to flower in successive years.