New study looks to find out what it takes to protect coastal swamp forests in Louisiana

Coastal swamp forests are perhaps one of the most iconic Louisiana wetlands. They are made up of mainly Cypress and Tupelo trees, supporting a wide range of ecosystem benefits, such as habitat for native species, carbon storage and storm surge protection for the coast. 

But these types of forests in Louisiana, facing rapid sea level rise, land subsidence and lack of fresh sediment from rivers, are particularly hard to protect and restore. A new study from the Louisiana Universities Marine Consortium suggests that river diversions can restore sediment and support the root growth needed for these forests to remain healthy. 

The trees and shrubs of coastal swamp forests are used to growing within water-heavy soils, the roots essentially binding together the fabric of Louisiana’s coast. When healthy, these forests can maintain themselves by collecting sediment spread by rivers and tides and building their roots into thick woven networks below ground. 

That natural process has become hindered by sea level rise and changes to the ways the Mississippi and Atchafalaya rivers carry much needed sediment. Because of that process changing, the study found that another factor is playing a key role in the declining health of these forests — too much water. 

“We have this weird situation in Louisiana where we have too much water because of the submergence, but we don’t have enough of the right water, which is seasonal river water pulses,” said Ken Krauss, executive director of science at LUMCON and author of the study published in the academic journal Forest Ecology and Management. 

Too much salty water can cause these roots to die. Sea levels are rising along Louisiana’s coast, moving further north through natural and manmade navigational channels carved throughout the wetlands. Dams, channels and levees higher up on the Mississippi River have reduced the amount of sediment carried down to Louisiana swamps, starving the swamp forests of the sediment it needs. 

The study found that these factors paired together with cypress and tupelo roots submerged in water for too long a time period deeply affects the health of these forests. The amount of healthy roots in the coastal swamp forests sites studied “was influenced by flooding as much as by salinity,” with less salty areas that had deeper and longer flooding still showing lower amounts of root growth, similar to the effect that salt has.

This has big implications for what kind of restoration these wetlands need, said Krauss. 

“Restoration-wise, we need to find a way to reconnect rivers with the forested wetlands,” he said. 

The study concluded that building back these roots in coastal swamp forests is critical to maintaining their health as sea levels continue to rise.

“With that river water will actually come sediment deposition, and that will help maintain the forested wetland,” added Krauss. 

Several areas in Louisiana’s Coastal Master Plan that are working to do just that, such as the Davis Pond river diversion project in Luling and the Maurepas Swamp diversion near Garyville. Krauss said that putting more emphasis on diversion projects such as these, particularly upriver in the coastal zone, will build more resilience into these vulnerable wetland forests.  

“In time, salinity is gonna kind of overwhelm a lot of these swamp forests,” he said. “The idea is that what can we do now to extend the life of these systems and in some places armor it such that we can sustain it.”