Ecological Succession In Salt Marsh Vegetation At Chongming Dongtan Wetland

Estuarine wetland is an important zone with interaction between land and ocean. In this special area, active ecological succession takes place. Research on ecological succession in estuarine wetland is the focal point in the studies of ecology, and would provide vital theoretical foundationf for wetland rehabilitation and reconstruction.In this paper, we sampled in Chongming Dongtan wetland, through on site survey and laboratory analyse, we studied the variation of importance value, life form, biodiversity, biomass and nitrogen concentration, tried to clarify characters in the process of vegetation succession. The main results are as follows:1. Ecological characters of salt marsh vegetation in successionFine-structured zonations refected succession process. Pioneer species Scirpus mariqueter Colonized and established near the barren area in low marsh, was gradually replaced by Spartina alterniflora and Phragmites australis along elevation. In the process of succession, importance value of Scirpus mariqueter decreased with the elevation, and which of Spartina alterniflora increased with the elevation in the beginning, then decreased near the dike. Importance value of Phragmites australis increased all the while. We could conclude that Scirpus mariqueter was the dominant species at low tidal marsh, Phragmites australis and Spartina alterniflora were dominant species at high marsh.In the area Spartina alterniflora and Scirpus mariqueter dominanted, biodiversity was very low, none other species existed, however, in the area Phragmites australis dominanted, biodiversity increased with hemicryptophyte, geophyte and therophyte plants appearing at the higher marsh.2. Temporal and spatial changes of vegetation biomass along successionBiomass increased with succession, biomass of early stage was low, as the representative of late stage, P. australis was much higher. As the colonizer, S. alterniflora possessed high biomass, provided huge productivity.All of three species had single peaks of aboveground biomass.The highest above ground biomass of S. mariqueter was observed in August, and those of S. alterniflora and P. australis were in July. Biomass of aboveground part ranged from24.98 g·m^-2to 388.00g·m^-2 for S. mariqueter, 137.26 g·m^-24244.40g·m^-2for S. alterniflora, and 115.49g·m^{-2 4}323.20g·m^-2 for P. australis. In a year long, the accumulate biomass increasement (ABI) of S. alterniflora was the highest, and in contrast, which of S. mariqueter was the lowest.ABI of S. alterniflora and P. australis were much higher...