Seed viability and dispersal of the wind-dispersed invasive Ailanthus altissima in aqueous environments

In mesic forest environments, seeds of wind-dispersed plant species may frequently be deposited in aqueous environments (e.g., lakes and rivers). The consequences of deposition in an aqueous medium depend on whether seed viability is maintained. If seeds survive there, secondary dispersal in water may transport seeds long distances to suitable habitats. Using the exotic species, tree-of-heaven (Ailanthus altissima [Mill.] Swingle), in this study we estimated seed dispersal into water as a function of distance and experimentally tested seed buoyancy, secondary dispersal, and germinability after dispersal in water and on land. We found that biologically significant numbers of seeds disperse directly into water, remain buoyant, and are transported long distances by water. Germination rates for seeds that were kept in aqueous environments (Cheat Lake and the Monongahela River, near Morgantown, WV) were found to be similar to or higher than those in nearby terrestrial controls (F = 10.94, P = 0.0057). Seeds kept in aqueous environments retained high germination rates (94.4 ± 1.1%) even after 5 months. Although A. altissima may not disperse primarily through water environments, this study suggests that secondary dispersal by water is possible and may allow for long-distance dispersal more than two orders of magnitude farther than recorded primary dispersal.