Landscape pattern changes of Carex and its response to water level in Lake Poyang Wetland

The formation and evolution of vegetation landscape are controlled by the hydrological processes in freshwater wetlands. Based on the Landsat TM/ETM+ remote sensing images, the landscape information on Lake Poyang Wetland in 1992, 1999, 2006 and 2012 was extracted by using decision tree classification. The spatial variation of Carex landscape was analyzed by means of landscape pattern index, transfer matrix and centriod shifting methods. Meanwhile, the relationship between Carex landscape and hydrological processes was also preliminarily discussed. Results showed that the distribution and area of Carex landscape in autumn were influenced by the water level and recession process of Lake Poyang Wetland during the study period, the slow recession of intermediate-elevation(14-16 m) areas and fast emersion of low-elevation(12-14 m) areas play a more important role in the formation and expansion of Carex landscape than the water level. The spatial pattern Carex landscape in Lake Poyang Wetland was closely related to the annual mean water level. In the year of low annual mean water level, the distribution elevation of Carex landscape is relatively low, some exposed mudflats were occupied by Carex landscape, and the original distribution areas of Carex landscape were partly replaced by Phragmites and Triarrhena landscape, the fragmentation degree of Carex landscape was relatively heavy. While in the year with high annual mean water level, many low bottomlands were submerged, the elevation of Carex distributed was relatively high. Many regions of Phragmites and Triarrhena landscape were occupied by Carex, while the original distribution areas of Carex landscape became partly mudflat or water landscape types. Affected by the rising water level, Carex landscape mainly shifted and centered on the high zones of estuary of input rivers and lakeshore, thus the fragmentation degree of Carex landscape was relatively light. In addition, water level inter-annual fluctuation will affect the centroid position of Carex landscape, with centriod shifting to the lakeshore during the rising water level; vice verse to the lake center during the falling water level falling. © 2017 by Journal of Lake Sciences.