Local competitive effects of introduced Spartina alterniflora on Scirpus mariqueter at Dongtan of Chongming Island, the Yangtze River estuary and their potential ecological consequences

Dongtan of Chongming Island, Shanghai, China is a wetland of international importance, in which dominant vegetation is Scirpus mariqueter community that supports a great diversity of bird species. Spartina alterniflora, native to the eastern and gulf coasts of the USA, was intentionally introduced to the tidelands of Dongtan in May 2001. Field work were conducted at Dongtan from March 2002 to May 2003 to determine how introduced S. alterniflora affects S. mariqueter population dynamics. The results obtained here show that S. alterniflora had strong competitive effects on S. mariqueter, and that the introduction of S. alterniflora to S. mariqueter community resulted in a significant decreases of S. mariqueter's abundance, coverage, seed and fresh corm output after two growing seasons. A concomitant consequence might be the decline in bird diversity. It is suggested that further introduction of S. alterniflora should be avoided to conserve the wetlands and their associated birds. A plan for controlling further spread of existing S. alterniflora populations in the Yangtze River estuary is urgently needed.