Genetic data were collected for glucose-6-phosphate isomerase locus 2 from a sample of the Acer saccharum Marsh. (sugar maple) embryo subpopulations of four forested patches in southwest Ohio and compared with the juvenile (1st-year seedlings to individuals ≤ 1.0 cm in basal area) and canopy (≥ 30 cm in diameter at breast height) subpopulations. Apparent gene flow into each patch was observed as certain alleles found in the embryo subpopulation were not observed in the canopy subpopulation. Genotype frequency data indicated that at least some of the gene flow could be attributed to seed dispersal. Although in some patches, the embryo subpopulation had lower genetic diversity than other subpopulations and was genetically differentiated, it is unlikely that these observed differences represent a change in the genetic diversity of future juvenile subpopulations. Key words: sugar maple, gene flow, genetic diversity, allozyme, forest fragmentation, seed dispersal.