Abstract: Expansion process of alien species is an important content of the study on management and control of ecological invasion. Based on the 1991, 1997 and 2007 remote sensing images of the coast of Yancheng, Jiangsu, expansions of Spartina alterniflora under different conditions were simulated and factors affecting the expansion and their intensities were identified with the aid of GIS technology and the Markov-CA model. Results show that (1) the actual annual expansion rate of S. alterniflora was 24.39% during the period of 1991-1997 and 7.76% during the period of 1997-2007, indicating that the species expanded rapidly in the former period and the expansion slowed down during the latter period; (2) the annual expansion rate of S. alterniflora, when the plants were let grow freely, was the highest, reaching 9.40% and 6.78% during the two periods, separately, and declined to 7.10% and 5.49%, separately, when growth of the plants was affected by competition of other species in the community and to 7.10% and 5.24%, separately, when growth of the plants was affected by both competition of other species in the community and artificial disturbance; (3) affected by competition of other plant species in the community, the annual expansions rate of S. alterniflora decreased by 2.30 and 1.29 percentage point,respectively, and affected by artificial disturbance, it did by 0 and 0.25 percentage point, respectively;and (4) the Markov-CA model built in this study can be used to get some valuable insights into the relationships between the expansion processes of exotic plant species and its affecting factors, which may provide some scientific basis for rational exploitation of wetland resources and conservation of biodiversity in the coastal zone of Yancheng.

Key words: expansion of Spartina alterniflora, Markov-CA model, affecting factor, identification, coastal zone of Yancheng