Abstract:

The Yangtze estuary is one of the most important stopover sites in East AsianAustralasian flyway for migratory waterbirds. Charadriiformes and Anseriformes are two major waterbird groups in the Yangtze estuary. During the past decades, suitable habitat for waterbirds in the Yangtze estuary has undergone severe changes due to the influences of natural factors (such as sea level rising, flow and sediment changes in the catchment and vegetation succession), as well as anthropic factors (e.g. reclamation, accretion promotion and deepwater channel construction). Based on remotly sensed data and field investigation, we studied the land use changes and applied spatial diversity and hemeroby index to evaluate the changes of habitat suitability for Charadriiformes and Anseriformes during the period of 1980-2010. According to the spatial diversity index, the Yangtze estuary was divided into four types, i.e., core habitat, secondary habitat, edge habitat and unsuitable habitat. The results indicated that the area percentages of core habitats decreased by 55.6% and 18.6% for Charadriiformes and Anseriformes, respectively. The area of core habitats decreased by 133 km2 for Charadriiformes and increased by 235 km2 for Anseriformes. The total area of secondary habitats, edge habitats and unsuitable habitats increased by 679 km2 and 311 km2 for Charadriiformes and Anseriformes, respectively. The comprehensive habitat suitability indices (H) for Charadriiformes were 0.92, 0.67, 0.58 and 0.53 for the years 1980, 1990, 2000 and 2010, respectively, with a decrease of 40% from 1980 to 2010. In addition, the comprehensive habitat suitability indices (H) for Anseriformes were 0.89, 0.72, 0.70 and 0.70 for the years 1980, 1990, 2000 and 2010, respectively, with a decrease of 18% during the last thirty years. Moreover, we found that the suitable habitats for Charadriiformes and Anseriformes both decreased more rapidly in the period of 1980-1990 than later periods. According to the spatial diversity indices of different hemeroby types, human disturbance was negatively correlated with the spatial diversity and had negative impacts on the habitat suitability of both Charadriiformes and Anseriformes. The degree of correlation for Charadriiformes was higher than that for Anseriformes. Moderate intensity of human disturbance increased the area of suitable habitat for Anseriformes. In summary, with intensive reclamation at the Yangtze estuary, habitat suitability for Charadriiformes and Anseriformes both decreased during the last thirty years， and habitat suitability for Charadriiformes decreased more rapidly than that for Anseriformes