Modeling Tidal Freshwater Forested Wetlands (TFFW) Habitat Changes for Land Management

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As tidal freshwater forested wetlands - TFFWs - are influenced by salinty due to salt water intrusion, they may experience changes in plant community composition, growth, and productivity. Models are needed to predict vegetation community change or dieback, as well as changes in carbon sequestration and storage due to changing climate, drought, changes in freshwater discharge, elevated carbon dioxide, and sea-level rise. 

Figure 1. Major study areas of the TFFW vegetation modeling system (Krauss et al., 2009)
Figure 1. Major study areas of the TFFW vegetation modeling system (Krauss et al., 2009)

Science Issue and Relevance: Many tidal freshwater forested wetlands (TFFW, or tidal swamps) in the southeastern United States are at least periodically influenced by salinity due to salt water intrusion especially during periods of drought, storm surge, or even strong tides. With the changes in salinity, salt tolerance of both woody and herbaceous plants may replace flood tolerance in controlling plant community composition, growth, and productivity. Therefore, advanced models are needed to predict vegetation community change or dieback, as well as change in carbon sequestration and storage, across the coastal gradient as a result of changing climate, drought, changes in freshwater discharge, elevated CO2, and sea-level rise.

Methodology for Addressing the Issue: USGS scientists and collaborators are developing a TFFW vegetation distribution model for sites in Louisiana, Georgia, and South Carolina (Figure 1). Historical data on hydrology, soil characteristics, elevation change, vegetation community distribution, and plant physiology are available for model calibration and validation. Vegetation modeling will be spatially explicit and process-driven and used to predict changes in vegetation community distribution triggered by changes in groundwater salinity, water level, and soil nutrients. Feedback mechanisms (positive and negative) between vegetation and physical environmental factors through evapotranspiration and plant nutrient uptake, influences on mineralization, decomposition, denitrification, and sulfate reduction will also be explored for incorporation into the modeling system (Figure 2). This model can provide a robust predictive tool (e.g., fish and wildlife refuges) for resource managers, and for generation of new scientific hypotheses in managing and studying the fate of TFFW under climate change, SLR, land-use change, elevated CO2, and freshwater management alternatives.

Figure 2. The vegetation model and other components of the integrated TFFW ecosystem modeling system
Figure 2. The vegetation model and other components of the integrated TFFW ecosystem modeling system

Future Steps: The process-based vegetation distribution model can be coupled with wetland morphology and soil biogeochemistry models (Figure 2) to examine TFFW carbon budget and greenhouse gas emissions in support of a national wetland carbon assessment.

Location of Study: Louisiana: 29°42’27.30’’N, 90°24’41.27’’W; South Carolina: 33°30’33.44’’N, 79°8’19.34’’W; Georgia: 32° 9’55.50’’N, 81° 8’4.86’’W