Plant communities of tidal freshwater wetlands of the continental USA and Canada
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Tidal freshwater wetlands (TFW) occur along the Gulf of Mexico, Atlantic, and Pacific coasts of the continental USA and Canada. Plant communities vary spatially across elevation, latitudinal, and disturbance gradients and temporally with season, between years, and over longer time scales. Patterns on a local scale are determined by seed availability, germination requirements, seed bank strategies, and tolerance of seeds and seedlings to stresses. Regional (estuarine) patterns involve tolerances to salinity and sedimentation, as well as hydrologic stresses. Latitudinal patterns may be a response to climatic gradients along the Atlantic coast and rainfall gradients on the Pacific coast. Annual species, which are important vegetation components, vary considerably. Causes of distribution changes or extirpations of rare/threatened species are poorly understood and impact of invasive species varies with location. Comparisons among Atlantic, Gulf, and Pacific coasts are limited by lack of data. Relatively little is known about tidal freshwater swamps or about West coast TFW. Species names follow a widely used US Department of Agriculture (USDA) web site (www.itis.usda.gov/index. html). In a few cases, a species name or variety is not accepted by ITIS; such taxa are designated as (NA) or not listed.