Climatic Controls on the Distribution of Foundation Plant Species in Coastal Wetlands of the Conterminous United States: Knowledge Gaps and Emerging Research Needs

Foundation plant species play a critical role in coastal wetlands, often modifying abiotic conditions that are too stressful for most organisms and providing the primary habitat features that support entire ecological communities. Here, we consider the influence of climatic drivers on the distribution of foundation plant species within coastal wetlands of the conterminous USA. Using region-level syntheses, we identified 24 dominant foundation plant species within 12 biogeographic regions, and we categorized species and biogeographic regions into four groups: graminoids, mangroves, succulents, and unvegetated. Literature searches were used to characterize the level of research directed at each of the 24 species. Most coastal wetlands research has been focused on a subset of foundation species, with about 45% of publications directed at just one grass species—Spartina alterniflora. An additional 14 and 8% have been directed, respectively, at two mangrove species—Rhizophora mangle and Avicennia germinans. At the national scale, winter temperature extremes govern the distribution of mangrove forests relative to salt marsh graminoids, and arid conditions can produce hypersaline conditions that increase the dominance of succulent plants, algal mats, and unvegetated tidal flats (i.e., salt flats, salt pans) relative to graminoid and mangrove plants. Collectively, our analyses illustrate the diversity of foundation plant species in the conterminous USA and begin to elucidate the influence of climatic drivers on their distribution. However, our results also highlight critical knowledge gaps and identify emerging research needs for assessing climate change impacts. Given the importance of plant-mediated processes in coastal wetland ecosystems, there is a pressing need in many biogeographic regions for additional species- and functional group-specific research that can be used to better anticipate coastal wetland responses to rising sea levels and changing temperature and precipitation regimes.