Assessing the ecological status of wetlands can provide critical information for the governance and management of wetland ecosystems.The index of biotic integrity (IBI) is a comprehensive method for assessing the ecological health of wetlands.Initially developed in North America,this method has standardized protocols for implementation and practice.The quantitative assessment results are easy to understand and communicate among scientific communities and the general public.Vascular plants are quickly emerging as one of the important indicators of human-mediated disturbances,because they are immobile,and therefore,susceptible to physical,chemical,and biological changes of the surrounding environment.Poyang Lake is the largest freshwater lake in China.The Poyang Lake wetland is recognized as one of the most important wetlands in the world since it provides habitats for many unique species of wintering migratory birds and is of prominent ecological and economic importance to millions of people in the middle and lower Yangtze River basin.Poyang Lake wetland has been significantly altered by human activities,such as agriculture,fishing,and tourism.Currently,there is no indicator framework to determine the status and trends of conditions of the Poyang Lake wetland.In this study,we aimed to develop a vegetation-based IBI (V-IBI) to assess the ecological health of Poyang Lake wetland.Field surveys of 30 sampling sites were conducted in the autumn of 2015.We collected data including plant species compositions,abundance,water quality parameters,soil properties,and land use surrounding sampling sites.We tested 35 candidate metrics regarding the diversity,structure,and disturbance tolerance of plant communities for their discriminatory ability between reference sites and impaired sites.Six metrics were finally selected as the V-IBI metrics,i.e.,numbers of invasive species,sensitive species,tolerant species,perennial species,species with both sexual and vegetative propagation,and percentage cover of Phalaris arundinacea L.Values of these metrics were scaled between 0 and 1.The V-IBI score of a sampling site was calculated as the sum of the scaled values of each individual metric.A 95% percentile of all V-IBI scores and quartiles of the scores below the 95% percentile were then used as cut-offs for rating categories.The results showed that 6 sites were rated as excellent (V-IBI ≥ 5.01);7 were good (4.38 ≤ V-IBI < 5.01);8 were fair (3.74 ≤ V-IBI < 4.38);7 were poor (3.10 ≤ V-IBI < 3.74);and 2 were very poor (V-IBI<3.10).Sampling sites rated as excellent and good were all located in western and northern sections,especially within the national and provincial nature reserves,whereas those rated as poor and very poor were mostly located in eastern and southern sections where wetland health was impaired by dense populations and intensive agricultural practices.Wetland areas where rivers discharged into Poyang Lake were generally rated as poor,suggesting that pollutants brought in by rivers had negative impacts on wetland health.The V-IBI was significantly correlated with the index of landscape development intensity (LDI) and qualitative habitat evaluation index (QHEI),indicating that V-IBI is plausible and reliable for assessing the ecological health of the Poyang Lake wetland.