Interpretive Summary: The differences in viability of the three seed types (CH, CL, and F-I) revealed in this study add support for focusing management efforts on Japanese stiltgrass populations in which CH seed production is highest, such as those along roadsides or in open areas exposed to higher light levels. The relative importance of the CH seeds suggests that Japanese stiltgrass has adapted to less-stable conditions (i.e., seeds that are a product of out-crossing are of more use than seeds that are product of self-fertilization). Nonetheless, Japanese stiltgrass produces large amounts of the less-viable CL seeds, which may enable it to maintain populations during stable conditions in the short term. Control treatments such as mowing (prior to flowering) stiltgrass populations in higher-light areas, such as roadsides, is a way to minimize CH seed output. Although any remaining upper CL flowers may transform into CH inflorescences, the amount of CH seeds produced should still be reduced. Treatment with herbicide of the roadside Japanese stiltgrass populations may better ensure that the forest interiors are not receiving a steady supply of CH seeds with comparatively high viability. The influence of regional moisture variation on Japanese stiltgrass seeds is less defined than the effects of light, but may be related to drought-induced seed dormancy of CH seeds. Seed longevity of both CL and F-I seeds is shorter in drier environments compared to seed longevity of CH seeds, which indicates that removal of Japanese stiltgrass populations that produce the most viable CH seeds may be even more effective in drier environments than in mesic environments. It is conceivable that after removing roadside populations of Japanese stiltgrass, small forest populations could eventually go extinct, especially under drier conditions.

Keywords: Chasmogamy, cleistogamy, Japanese stiltgrass, light, Microstegium vimineum, moisture regime, seed longevity, seed viability