Long-term Trends in Swamp Tree Growth across Drought and Salinity Gradients along the Northern Gulf Coast

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This study will examine the potential effects of climate-change-induced sea level rise, drought and water extraction by examining tree growth patterns across the Gulf Coast, specifically targeting long-term research plots available in the North American Baldcypress Swamp Network (NABCSN) and the Suwannee River.

Swamp tree growth study sites on the southern United States

Swamp tree growth study sites on the southern United States

The Science Issue and Relevance: Freshwater species along rivers of the Gulf Coast lie along freshwater tidal to fresh riverine gradient, but tree production and growth are lower where salinity is higher. Also, the Gulf of Mexico lies along a geographical gradient of temperature, evapotranspiration and drought from Texas to Florida. This study will examine the potential effects of climate-change-induced sea level rise, drought and water extraction by examining tree growth patterns across the Gulf Coast, specifically targeting long-term research plots available in the North American Baldcypress Swamp Network (NABCSN) and the Suwannee River.

 

Methodology for Addressing the Issue: These studies will be conducted in long-term research sites along the Suwannee River National Wildlife Refuge and the Gulf Coast portion of the North American Bald Cypress Swamp Network. Suwannee transect plots were set up in 1996-99 by the U.S. Geological Survey in cooperation with the Suwannee River Water Management District to assess floodplain forest and subcanopy composition, as well as projected change resulting from altered river flows. NABSCN Gulf Coast plots were set up after 2006, and have replication at the landscape level, with five replicate swamps per geographical location. All sites are near USGS gages providing continuous records of water discharge and salinity. The Suwannee plots were relocated in 2014 and oriented along river flow and salinity gradient. Forest tree mensuration techniques were used to establish these plots wherein all surviving trees will be re-measured to determine shifts in growth and species composition over the past 15 years. Trees in NABSCN are outfitted with tree growth bands, and have measured annual tree growth in the last 5-10 years (Neches River TX, Mississippi River LA, and Sopchoppy/Aucilla River FL). NABSCN sites also have a suite of data on ecosystem function (production and regeneration) and environment (water level, sediment and salinity via recorders and Sediment Elevation Tables).

Future Steps: The project will help predict climate change responses of freshwater species by tracking responses of tree growth to salinity and flow shifts. Managers can use the information to design water management strategies to maximize swamp forest health. The study will dovetail with an on-going groundwater salinity intrusion and production study with Dr. David Kaplan, University of Florida Dept. of Engineering Sciences, Gainesville, Florida.