United States Biogeographic Regions, Coastal Wetlands, and Climate

Maps of the conterminous United States identifying the 12 assigned biogeographic regions (a) and the distribution of dominant plant groups in coastal wetlands (b) in relation to the Global Aridity Index (c) and winter temperature extremes (d). Within each biogeographic region, coastal wetland plant communities are generally dominated by a common set of foundation plant species. In panel b, blue indicates graminoid dominance (e.g. grass-like plants), red indicates mangrove dominance, yellow indicates succulent plant dominance, and black indicates primarily unvegetated wetlands (e.g., salt flats, salt pans) often dominated by algal mats. Whereas winter temperature extremes govern the transitions from mangrove to graminoid dominance (see red to blue transitions in panel b, which occurs in Florida), aridity and salinity tend to govern the transitions from graminoid to succulent dominance and the absence of vegetation (see transitions from blue to yellow or blue to black in panel b, which occur in Texas and California). The Global Aridity Index represents the ratio of precipitation to potential evapotranspiration. (Figure 1 in Osland et al., 2019)