Growth and Survival of Avicennia germinans Seedlings in a Mangal/Salt Marsh Community in Louisiana, U.S.A.
Coastal Louisiana is at the latitudinal limits of the black mangrove, Avicennia germinans. Salt marshes dominated by Spartina alterniflora form ecotones with this mangrove species at Bay Champagne, Louisiana. Plant species zonation is distinct with a bay-edge zone dominated by A. germinans, an inland zone dominated by S. alterniflora and an intermediate (transition) zone containing both species. Avicennia germinans is occasionally found in the higher elevation areas of the Spartina zone (Spartina high), but never in the lower areas (Spartina low). Analyses of diameter growth, height growth, and above and below-ground biomass showed that A. germinans could grow in soils permanently flooded for 13 months in a greenhouse, and that growth inhibition of A. germinans by S. alterniflora occurs under these conditions. In a field experiment, A. germinans seedlings were transplanted into randomly located plots in the Avicennia, Spartina high and Spartina low zones. Survival was marginally lower in the Spartina low zone than in the other zones, but almost half of the plants survived there. However, diameter and biomass of the surviving transplants were significantly lower in both Spartina zones than in the Avicennia zone, possibly due to growth inhibition by S. alterniflora in combination with a greater hydroperiod in the Spartina high and low zones.