The Effect Of Spartina Ecological Management Project On The Tidal Flat Habitat Of Grus Monacha In Chong-ming Dongtan

Chong-ming Dongtan is one of the most important salt marshes at the Yangze Estuary. It provides an excellent wintering habitat for Grus monacha due to its superior resources and environmental conditions, which contributes to the stability of the population. This study focuses on the change of the main environmental factors during the Spartina alterniflora management project in the Nature Reserve of Chong-ming Dongtan, its impact on salt marsh vegetation and wintering habitats for Grus monacha. The results include:1. The salt marsh plants are distributed in belts and the communities are unstable before the Spartina alterniflora management project was carried out at Chong-ming Dongtan. Six dominant plant species are distributed parallel to the direction of Levee 1998. The Gramineae mainly located near the levee, while the Sedge neighbor the mudflat. We divided the dominant species into four groups:Phragmites australis, Scirpus mariqueter - Spartina alterniflora, Carex scabrifolia - Scirpus triqueter -Juncellus serotinus, and Imperata cylindrica - Echinochloa crusgalli based on the Spearman rank correlation analysis of coverage among the species with Important Value above 1.5%.2. The tidal flat elevation as well as the soil salinity increased significantly after the Spartina alterniflora management project. It deposited quickly in the northern part of Xiaobeigang tidal channel and the average vertical deposition rate in the Spatrtina alterniflora and Scirpus marqueter zone increased to 400 mm per year from 2013 to 2014, which exceeded the average deposition rate of previous six years from 2006 to 2012. The soil salinity in the Scirpus marqueter zone increased significantly at the same time. We used CCA (canonical correspondence analysis) to sort the categories of salt marsh vegetation, tidal flat elevation and soil salinity, and found the results are similar to the ecological groups derived from Spearman correlation, which suggests that the tidal flat elevation and soil salinity are the key environmental factors of the vegetation distribution. Therefore the variation of these two factors may change the distribution of the plants and the Grus monacha’s wintering habitat.3. Based on controlled experiment, we found that bulb growth of the Scirpus marqueter had best performance at salinity 1.0-1.5%, while 3-6 cm burial provides the best condition for seedling germination. Both the number and the whole weight of Scirpus marqueter bulbs increase with the increase of salinity, while they begin to decline if the salinity increases further. In addition, soil is necessary to the germination of Scirpus marqueter. Proper soil burial can increase the germination rate, enhance the competitiveness of the species, while excessive seed burial will decrease the germination rate and speed. Therefore, the reproductive and the competitiveness of Scirpus marqueter will be suppressed under high sedimentation rate. The food supply for Grus monacha will be reduced.4. The core habitat is mainly distributed to the south of Xiaobeigang tidal creek, while non-suitable habitat is mainly to the north of the tidal creek. Grus monacha prefers the sedge community, with low vegetation height and easily accessible food, rather than the Phragmites australis or Spartina alterniflora communities. We established the habitat suitability index model based on the Spartina management project and found that the vegetation type, coverage, height, tidal height and frequency and distance to levee affected the birds. According to these data, the core habitat area for Grus monacha was derived as 697 hm2, secondary suitable habitat 469 hm2, marginally suitable habitat area 282 hm2 and the non-suitable habitat area 352 hm2.5. Little was affected on the wintering population of Grus monacha and their habitats during the first phases of Spartina management project. The number of Grus monacha increased year by year from 2012 to 2015, which was not affected by the management project in 2013. The number of the Grus monacha and the reclamation location had a close relationship:on the one hand, the number of birds decreased obviously when the Tuanjie shoal was reclaimed. On the other hand, the Sedge community area and the number of the Grus monacha kept the same trend based on the historical data. Since the project was main conducted in the Spartina zone of Dongwang shoal, the effect on the Grus monacha population at our study area rather limited.Overall, in the short term, Spartina alterniflora management project at Chong-ming Dongtan has little effect on the wintering population of Grus monacha and their habitats. With the improvement of the quality of habitats inside and outside the new levee, the area of Grus monacha’s wintering habitat is anticipated to increase.