Spatial and temporal variations in salt-marsh vegetation in Wanggang area,Jiangsu coast,based upon TM imagery analysis

Wanggang area is a typical region of tidal flats.In the 1960s and 1980s,Spartina anglica and Spartina alterniflora were artificially introduced, respectively,to this area.Appearance of Spartina marshes changed the sedimentary environment of the tidal flats.Using Landsat-TM data,the vegetation change and consequent modifications to the geomorphology of the tidal flat system were analyzed.Firstly,field observation and sampling were undertaken to investigate the biological feature of the three main salt-marsh species: Suaeda salsa,Spartina anglica and Spartina alterniflora.Observations in the four different seasons show that summer represents a period of rapid growth.In autumn the plants have the highest biomass.Thus,3 Landsat-TM images from 29 July 2002,24 July 2003 and 28 October 2003 were used to map the vegetation distribution and annual change.Using the in situ data,spectral features obtained show that Bands 3,4 and 5,in combination with field observations,contain sufficient information to distinguish the 3 different kinds of plants.Supervised classification using Bands 3,4 and 5 with in situ calibration was performed to derive the distribution pattern of the vegetation in Wanggang areas.The result shows that:(1) Spartina alterniflora is expanding towards the sea,with a rate of several hundred meters per year;(2) in the upper part of the inter-tidal zone,Suaeda salsa and Spartina anglica are distributed near the sea dyke,but reclamation has reduced the area of these two kinds of marshes;and(3) from 2002 to 2003,the area covered with Spartina alterniflora increased by 18%.