Many plant populations produce large seed crops in some years but not others. This phenomenon, known as mast-seeding, is commonly know to increase reproductive success by economies of scale, such as satiating seed predators and increasing pollination efficiency in mast years. However, less is known about how seed production becomes synhcronized among individual plants within populations. I explore the causes of mast-seeding in three mast-seeding plant species: Astragalus scaphoides, a perennial herb, Pinus albicaulis, a tree of conservation concern, and Acer saccharum, an economically important tree. All three species experience fitness benefits of masting. The physiological mechanism of synchrony is “pollen coupling”, in which plants deplete resources in mast years, and are synchronized by density-dependent pollen limitation. Mathematical models of pollen coupling are mathematically chaotic, meaning that masting would occur even under perfectly constant environmental conditions, but small changes in the environment could cause large changes in mast cycles. This phenomenon emphasizes the connections between processes at physiological, population, and community levels.