Freshwater Forested Wetlands of the Southeastern US: Trends In Aboveground Productivity In Relation to Hydrology and Salinity.

Freshwater forested wetlands are productive ecosystems due in part to the quantity of nutrients received during overbank and, in some cases, tidal flooding. We have documented changes in forest structure and growth of trees in swamps of South Carolina, Georgia, Alabama, and Louisiana from 1988-2010 subject to a variety of flooding regimes.  Baldcypress (Taxodium distichum), water tupelo (Nyssa aquatica), and swamp blackgum (N. sylvatica var. biflora) are the dominant flood tolerant species that occur in these wetlands with species abundance varying tremendously from one area to another depending on hydrologic conditions.  Community response to environmental change often occurs over a period of years, thus indicating the need for long-term studies.  While litterfall estimates seem to be well defined with 3–5 years of data, stem growth across hydrological gradients in some areas are still not clear even with 10 years of data.  We found that salinity, soil total nitrogen, flood duration, and flood frequency affected forest diameter increment, litterfall, and basal area the greatest.  Salinity concentrations of 1.3 g/L drastically decreased basal area increment growth rates and litterfall production.  As estuarine influence shifts inland with sea-level rise, forest growth becomes linked to salinity and perhaps salinity-induced changes in nutrient availability.  These changes in soil nutrients can be slow to affect the ecosystem, but have long-lasting effects on productivity and permanent changes in the composition of forest stands.