Floodplain forest species are presumed to interact strongly with the environment, as evidenced by pronounced spatial variation in flood-driven abiotic constraints and forest composition. These data describe functional diversity and environmental characteristics for 156 forest assemblages sampled on floodplain landforms within transects from the lower peninsula of Michigan. The functional diversity of each assemblage is characterized by two metrics of functional richness (Convex Hull Volume/CHV and Trait Onion Peeling/TOP), one metric of functional dispersion (FDis), and community weighted mean functional trait values. Functional diversity metrics were calculated from 12 quantitative and qualitative functional traits extracted from public datasets following published methods. Environmental attributes are characterized for each assemblage for multiple spatial scales (e.g., transect level, landform level, and within-landform level) and include transect type, measures and classes of landform relative elevation and distance to channel, and characterizations of microtopography. The data are intended for use in analyses of relationships between floodplain forest functional diversity and environment.