Abstract:

Aims This study investigated the pattern of expansion of the exotic Spartina alterniflora for seven years after its introduction into the neonatal Jiuduansha shoals in the Yangtze River estuary, Shanghai. These time-based data are an important first-step in providing a scientific basis for wetland management and biodiversity conservation.

Methods Remote sensing (RS), combined with geographical information systems (GIS) and global positioning systems (GPS), was used to map the distribution of S. alterniflora salt marshes on the Jiuduansha shoals. Findings were checked using field surveys of selected areas.

Important findings S. alterniflora populations expanded from 100 hm² in 1997 to 1 014 hm² in 2004. The pattern of expansion was typical of invasions, i.e., initial colonization, a lag time and rapid population growth and range expansion. In the first year (1997) of planting, S. alterniflora populations colonized the shoals, and about 35 hm² S. alterniflora survived. The period between 1998 and 2000 was a lag time with a mean annual expansion rate <1%. The onset of rapid population growth and range expansion began in 2000, and the annual expansion rate increased to 25%-116%, which exceeded the indigenous species and indicated the strong competitive capability, rapid range expansion and wide ecological niche of S. alterniflora. RS, combined with GIS and GPS, provides a potential tool for monitoring population dynamics and range expansion of invasive species on a large scale. Results of this study indicate this approach can provide timely data for biodiversity conservation of intertidal zones, resource management and sustainable development on coastal regions.

Key words: Jiuduansha shoals, exotic plant, Spartina alterniflora, remote sensing analysis, population dynamics