湿地植被的时空变化研究是陆地生态系统对全球变化响应研究的重要内容之一。利用2000—2015年的中分辨率成像光谱仪(MODIS)16天合成的植被指数数据(NDVI和EVI)作为植被覆盖的指标,采用基于像元的线性趋势分析和稳定性分析方法研究了南四湖湿地植被覆盖的时空演变和稳定性格局特征,并结合气象数据和相关资料分析了控制植被覆盖变化的主要因素。结果表明:1) 南四湖湿地植被覆盖度受景观格局控制,呈现由湖岸向湖心减小的带状分布特征。2) 南四湖植被覆盖变化具有阶段性特征。2000—2003年生长季植被覆盖度处于较高水平,2004—2006年处于较低水平,之后波动变化;植被覆盖年内变化呈双峰特征,尤其在下级湖。3) 湿地的水陆交错地带植被覆盖下降趋势明显,植被指数平均每10年减少0.1~0.3,其他区域植被覆盖略有上升。4) 植被覆盖的稳定度亦呈现以湖心为中心的环带状特征,由湖心到湖岸植被的稳定性逐渐增高。5) 植被覆盖度的变化与区域降水导致的湖泊水位变化关系密切。除去极端降水的2003年,年降水量与湿地植被指数呈显著负相关关系(P<0.05),相关系数分别为-0.60(NDVI)和-0.66(EVI)。作为南水北调东线工程重要的水利枢纽,南四湖频繁的水文调蓄必然影响湿地植被覆盖格局,进而影响南四湖湿地生态过程及生态功能,需引起管理者的重视。

Spatial and temporal change study of wetland vegetation is an important part of the global change and terrestrial ecosystem research.We selected vegetation index(NDVI and EVI)data of Moderate Resolution Imaging Spectroradiometer(MODIS)during 2000 to 2015 as indicators to represent vegetation cover.Using pixel-based linear trend analysis and stability analysis method,we studied the vegetation coverage temporal and spatial evolution and vegetation stability pattern of Nansi Lake,and combined with meteorological data and other related data to analyze its control factors.The results show that:1)Vegetation coverage of Nansi Lake was controlled by landscape pattern,with a reducing banded distribution from the lake shore to the eulimnetic area.2)Vegetation coverage change had stage characters.Vegetation coverage was at a high level in growing season from 2000 to 2003,at a low level from 2004 to 2006 and fluctuated after 2006.Vegetation coverage had bimodal trends within the year,especially in the lower lake.3)Vegetation coverage decreased significantly at the lake-land ecotone in Nansi wetland.Vegetation index decreased by 0.1 to 0.3 per 10 years averagely,and it increased slightly at other regions.4)Stability of vegetation coverage presented the annular characterized,increasing from the central to shores of the lake gradually.5)Vegetation coverage has the close relationship with regional precipitation and lake level change caused by precipitation.Except the extreme precipitation year(2003),annual precipitation and wetland vegetation index showed a significant negative correlation(P<0.05),and correlation coefficients were -0.60(for NDVI)and -0.66(for EVI).As an important hydro-junction at south-to-north water transfer east route project,frequent hydrological regulation in Nansi Lake inevitably influences wetland vegetation coverage pattern,even affecting the Nansi Lake ecological processes and functions,to which relevant managers should pay serious attention.