Seed bank dynamics of blowout penstemon in relation to local patterns of sand movement on the Ferris Dunes, south-central Wyoming

Abstract

Plants restricted to active sand dunes possess traits that enable both survival in a harsh environment and local migration in response to a shifting habitat mosaic. We examined seed bank dynamics of Penstemon haydenii S. Watson (blowout penstemon) in relation to local sand movement. We measured within-year sand movement along a 400 m transect and examined plant density, seed production, and seed density in relation to this movement. Plant densities were highest in areas of moderate sand movement. Annual seed rain averaged 13 seeds·m−2, whereas persistent seed bank density (0–10 cm depth) averaged only 0.1 seeds·m−2. A laboratory burial experiment with nondormant (chilled) seeds showed that most deeply buried seeds (>6 cm) were held in enforced dormancy under spring conditions, while seeds at intermediate depths (4–6 cm) were induced into secondary dormancy that was broken by subsequent drying and re-chilling, thus promoting seed carryover until the following spring. Most near-surface seeds produced seedlings. Enforced and secondary dormancy provide mechanisms for maintaining a persistent seed bank of more deeply buried seeds that could become part of the active seed bank as sand movement re-exposes them near the surface. This could facilitate both population persistence and migration as previously occupied habitat becomes unsuitable.