Use of sediment amendments to rehabilitate sinking baldcypress swamp in coastal Louisiana: 2. Vegetation characteristics

Middleton, Beth; Jiang, Ming

Forested wetlands are sinking in certain coastal areas of the world, so that the vegetation there might benefit from an increase in elevation accomplished via sediment placement. This study compared the vegetation characteristics of Taxodium distichum swamps in southern Louisiana with sediment amendments added to those of natural coastal swamps, with respect to tree growth, below-ground production, tree regeneration, and herbaceous vegetation composition. After sediment application in January 2007, both of the stands of sediment amended swamps had higher elevation and salinity levels than the natural swamps. The stand of sediment amended swamp with the highest elevation (Site 1) had little or no tree growth and some dying trees of T. distichum. The sediment amended swamps had higher root biomasses than the natural swamps. The higher biomass was not an indication of enhanced root growth of the in-situ trees because the root biomass was contributed by species that established after sediment placement (e.g., Salix nigra and Acer rubrum var. drummondii). Furthermore, after sediment placment, there was little increase in circumference of T. distichum, and the ground vegetation generally had lower species richness and cover. While other studies have found that sediment amendment can have positive effects on the vegetation of inundated coastal salt marsh, our study did not find any immediate positive response with respect to tree growth in coastal T. distichum. The layer of sediment placed in the study plots in this project was relatively deep, but shallower amendments could be tested to determine any benefits to sinking T. distichum swamps.

Use of sediment amendments to rehabilitate sinking baldcypress swamp in coastal Louisiana: 2. Vegetation characteristics

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