Stability of coastal systems are threatened by oceanic and atmospheric drivers of climate change. Sea-level rise compounded with increased frequency and intensity of storms emphasizes protection of inner island systems by dune formations. Dune building processes are affected by feedbacks between growth of ecosystem engineering dune grasses and environmental drivers associated with disturbance such as sand burial and salt spray, but functional roles of these species are poorly understood. Further, complications arise as temperatures increase with climate change. Thermal niches of some species may experience a latitudinal expansion, causing an emergence of competitive interactions that were previously absent. Topographic structure of coastlines, traditionally influenced by burial and salinity, will be escalated by water stress and species competition as climatic shifts occur. Ammophila breviligulata, a northern dune grass, creates tall continuous dunes ridges, while Uniola paniculata, a southern dune grass with expected northward expansion, builds interspersed hummocky dunes. Spartina patens maintains low elevation topography and is found along the moisture gradient of islands. Our research shows that physiological and functional trait responses (SLA, biomass, and maximum root length) differentiate these three ecosystem engineering dune grasses based on varying environmental drivers (sand burial, salinity, and water stress). Functional trait metrics also predict resulting biotic relationships that arise from competitive emergence. All of these factors will influence dune topography and barrier island formation causality.