Abstract
Hydrological properties are driving forces of wetland systems. The influence of water level fluctuations on vegetation distribution is of growing interest as wetlands are increasingly disturbed by climate change and intensive human activity. Based on time series MODIS (Moderate Resolution Imaging Spectroradiometer) imagery from 2000 to 2012, we investigated the spatial–temporal dynamics of wetland vegetation in Poyang Lake using a combined Sen’s slope and Mann–Kendall (MK) test approach, and explored their correlations with water level fluctuations in different hydrological periods. The results showed that more than 34% of wetlands at lower elevations of Poyang Lake had experienced an increasing trend in the enhanced vegetation index (EVI), whereas EVI in about 11% of the wetlands at higher elevations decreased significantly. Responses of grassland area extracted from MODIS EVI were found to be more sensitive to water level fluctuations in the southern lakes. The change rate of grassland area decreased with the rising water level during the rising period, but increased with the rising water level during the retreating period. Correlations between grassland area and water level were much weaker in the dry period. In addition, we found fluctuations of the main water body had negligible effect on grassland area since the water level at Xingzi station was below 14 m. These results provide new insights for predicting future changes of wetland vegetation influenced by the ongoing threats from climate change and human activity, and form a foundation for ecosystem management of Poyang Lake.
Highlights
As the primary producer of wetlands in the coastal zone and around lakes and reservoirs, wetland vegetation is an internationally important biodiversity resource
Water level fluctuations are a decisive element in the water regime, which is determined by water depth and the rate, duration, frequency, amplitude, and timing of flood or draw-down events [12,13]
Y = cexp − ( x − u)2 /t2 where y is the relative abundance of each classification of vegetation dynamics within each elevation gradient; x is the DEM data in this paper, derived from the National Geometrics Centre of China; c is the maximum of abundance; u is the peak of elevation, which appears when y equals to c; and the full width of half maximum (FWHM) is 4t
Summary
As the primary producer of wetlands in the coastal zone and around lakes and reservoirs, wetland vegetation is an internationally important biodiversity resource. The condition of fish and wildlife habitat, patterns of biotic succession, species richness, biodiversity, productivity and spatial distribution of wetland plant communities are dependent on water level fluctuations of varying frequency and amplitude [14,15,16]. Numerous studies have attempted to relate specific environmental factors and individual plant species for the Poyang Lake wetland community in relatively narrow spatial scales: from a typical belt less than 1 km2 [30,31] to a reserve covering hundreds of km2 [32]. Xu et al (2013) further noted that species richness and Shannon–Weiner indices of three plant communities were significantly correlated with water table depth and the soil moisture gradient [31]. Relateto hydrological processes to wetland vegetation dynamics wide spatial and temporal scales
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