Abstract

In general, many of the swamps of coastal Louisiana, U.S.A., are highly degraded, and several are converting to marsh and open water. The initial purpose of this study was to determine the feasibility, and potential benefits, of reintroducing waters of the Mississippi River into the degraded Maurepas swamp, located in the Pontchartrain Basin of southeastern Louisiana. Early in the year 2000, 20 sites were selected in three different habitat types characterized by moving fresh water (throughput sites), stagnant, nearly permanently flooded (relict sites), and areas prone to saltwater intrusion events (degraded sites). Paired 625-m2 plots were outfitted with litter-fall traps, herbaceous subplots, and wells for measuring interstitial soil salinity. From 2000–2006, diameter growth was followed for 2219 trees, and herbaceous production was estimated using mid- and late-growing season clip plots. Overall, primary production was dominated by trees early in the study, but switched to herbaceous vegetation as parts of the ecosystem converted from swamp to marsh. Salt stress was the primary cause of tree mortality in areas of low density, whereas stagnant standing water and nutrient deprivation appear to be the largest stressors at interior (relict) sites. The 2005 hurricanes caused wind throw of up to 100% of midstory trees in areas of low canopy density and was negligible when basal areas of baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) were greater than 30 m2 ha−1. Using spectral signatures of the 625-m2 plots, the aerial extent of habitat types revealed that the vast majority of the Maurepas swamp is either relict or degraded. Without a river reintroduction in the near future, as well as harnessing other point and nonpoint sources of fresh water, the Maurepas swamp will continue its clear trajectory to marsh and open water.

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