A survey of vascular plant species at Gooseberry Island Nature Preserve, a 5.56 ha forested island, was conducted during the 2004 growing season. This study was undertaken to document the composition and structure of the vascular flora and to provide baseline information for land management decisions. A young second growth wet floodplain forest and an old-growth mesic floodplain forest community was quantitatively sampled. The wet floodplain forest community was dominated by Acer saccharinum (silver maple) with some Salix nigra (black willow). The mesic floodplain forest was dominated by Aesculus glabra (Ohio buckeye), Acer saccharum (sugar maple), and Quercus macrocarpa (bur oak). Bur oak, a dominant species in the largest tree size classes, was only a minor element in the lower tree size classes and was absent from the shrub and sapling layers. Historical data from 1977 indicate that in the last 30 years there has been a significant increase in buckeye and sugar maple. A total of 162 species in 126 genera and 62 families were encountered, including 35 taxa near the northern limits of their range.