Maurepas Swamp Restoration
The Maurepas Land Bridge is a critical line of defense in reducing risk from storm surge for communities around Lake Maurepas as well as East Baton Rouge. Historically, the land bridge was covered with swamp forest dominated by bald cypress trees. The entire land bridge was clear cut in the late 1800’s and early 1900’s when logging of cypress peaked in the region. While some natural regeneration occurred, it was limited by the introduction of nutria, lack of nutrient freshwater and sediment input due to the leveeing of the Mississippi River, and subsidence. The construction of the MRGO, which introduced higher salinity to Lake Pontchartrain and Lake Maurepas, also had an effect on the remaining cypress stands. Currently, on much of the land bridge, natural cypress regeneration is not possible because the swamps are permanently flooded and seedlings need a period of draw down to germinate. In other areas, the swamp forest has already converted to marsh. Additionally, a severe drought in 1999 and 2000 in the region caused salinity in the area to spike and killed many trees, both naturally occurring and planted.
Logging Historic logging operations using a pullboat in a Louisiana bayou. The huge steam engine drove a drum which hauled the logs out of the swamp, creating deep grooves (left, photo courtesy New York Public Library). These operations created scars that can still be seen on the landscape as narrow parallel or wheel spoke patterned canals (right, photo from 2010).
In the past, swamp restoration projects on the landbridge have failed, mostly due to high salinity. During the drought of 1999 and 2000, salinity in the Maurepas area reached 10 ppt, and tens of thousands of re-planted trees were killed. LPBF believes that with the closure of the Mississippi River Gulf Outlet (MRGO), the risk for high salinities has diminished. We have observed a freshening of the basin since the closure. With lower baseline salinities, and the construction of the proposed West Maurepas Freshwater Diversion, the risk to swamps trees during drought may be diminished.
Swamp Restoration on the Maurepas Landbridge
Swamp regeneration often does not occur in southeast Louisiana because of nutria herbivory, high interstitial soil salinity, altered hydrological regimes and slow germination rates. Under existing conditions, without human intervention, bald cypress seedling mortality is quite high.
LPBF has begun a planting program on the Maurepas Landbridge modeled after our program at the Caernarvon Freshwater Diversion. The goal planting program is to contribute to large-scale, long-term restoration in the Pontchartrain Basin. LPBF and our partner, Restore the Earth Foundation (REF), are committed to swamp reforestation on a large enough scale to restore the habitat for animals and storm surge benefits for the surrounding communities.
LPBF has conducted various swamp tree plantings on the Maurepas Landbridge since 2013 in partnership with the REF and with the help of many dedicated community volunteers. Our volunteers help transport, space and plant the trees, as well as outfit them with nutria protectors. Nutria protectors are a critical component of tree survival as trees without protection are readily eaten or destroyed by the prolific rodent. In addition to volunteer plantings, there has also been commercial plantings, supported by REF, where thousands of trees are planted in one week.
Volunteers having fun in the mud, helping to restore the beautiful swamps on the Maurepas Landbridge.
We have been solely responsible establishing and conducting the monitoring of the planted trees. Under this program, a percentage of all the trees that are planted are tracked over time for survival and growth rates. This allows for accurate estimations of success of the plantings over time. The monitoring includes scientific data collection and analysis. For each tree, the survival is assessed and diameter at breast height (DBH) and height are measured. The data is analyzed to produce growth rates for trees by planting (over time), by species and by location. The data provided from the monitoring program has proven to be invaluable for showing success of this project and providing lessons learned for future plantings to improve success.
Monitoring the growth rates and survival rates of the tress is important to show success and learn lessons that make future restoration plantings more successful. Each tree in the monitoring program is tagged with a unique number (top left), measure for height (top right) and diameter at breast height (bottom left). If the tree is not tall enough to get diameter at breast height, then the basal diameter is measured (bottom right).
Natural Swamp Regeneration on the Maurepas Landbridge
While we were scouting for planting areas in July of 2015 we found a large swath of the land bridge where we believe natural swamp regeneration is occurring. We spotted adult swamp species, such as water tupelo and cypress seeding, and younger trees of different ages growing and thriving. There was also a swamp community understory developing, such as palmetto and swamp red maple. In addition, the sounds of the swamp were alive. Insects were buzzing, birds were chirping and life of all kind abounded. We confirmed our previous observations and discovered a possible gradient of regeneration with more regeneration occurring on the southern end of the land bridge and less regeneration moving northward. We also tested the soil salinity and found is was lower than the 3.0 ppt threshold for cypress. This is very exciting since this area was hit hard by the drought in 1999 and 2000 and high rates of mortality for natural and planted trees were reported in the area after the drought. LPBF would like to gain an understanding of natural regeneration in swamp habitats and study the conditions and processes under which it occurs. LPBF is currently pursuing funding to set up long term plots to study the natural regeneration over time.
There are swamps on the Maurepas Landbridge, south of Pass Manchac that seem to be naturally regenerating. A combination of dead cypress, live adult cypress and cypress sapling can be seen in many areas (top left, young cypress is the lighter colored tree in the foreground), areas further south have healthier swamps with denser canopies, the goal for the entire landbridge (top right), small, healthy looking cypress seedlings were seen (bottom left), and tupelo seedlings and saplings were found among the bull tongue and other understory fresh marsh species (bottom right, water tupelo sapling is the small tree towards the rear of the photo, in the middle).