Vegetation dynamics on mid-channel bars (MCBs) is essential for supporting ecosystem functions and associated services in river systems, especially in dammed large rivers. Generally, there are two possible changing patterns that vegetation of MCBs downstream a dam would experience. On one hand, the vegetation area may shrink because of a decrease in the MCB area in the post-dam period, which has been observed in many rivers around the world. On the other hand, the MCB vegetation area may expand because flood disturbances would be weakened by dam operation. However, little evidence has been reported to clarify such confusion. Therefore, vegetation dynamics of MCBs in the mid-lower Yangtze River downstream the Three Gorges Dam (TGD; the world’s largest dam) is selected as a case study to address the issue. Using long-term (1987–2017) Landsat archive images, this study reveals the spatiotemporal variations of vegetation area change intensities (VACIs; indicated by dynamic trends) on MCBs in the mid-lower Yangtze River. Results show that an overall VACI in the post-dam period (2003–2017) is about three times faster than that in the pre-dam period (1987–2002). In other words, the rate of vegetation colonization accelerated after the TGD operation began in 2003. Moreover, the VACIs in the post-dam period are size dependent, where large size MCBs are likely to gain higher VACIs: Small-sized MCBs (0.33 km²/yr), medium-sized MCBs (1.23 km²/yr), large-sized MCBs (1.49 km²/yr). In addition, VACIs of individual MCBs in the post-dam period are distance dependent, where the further a MCB was from the TGD, the higher the VACI. It is also suggested that the weakened flood disturbances in the post-dam could explain the rapid vegetation growth and colonization. This work is not only beneficial for managing and protecting MCBs downstream the TGD after its operation, but is also helpful in understanding vegetation dynamics of MCBs in other dammed river systems around the world.

As an important geographical position in China, the middle and lower reaches of the Yangtze River play an important role in the construction and development of the Yangtze River Economic Belt. The evolution of mid-channel bar (MCB) has a good reference value for wetland protection and waterway safety, and the dynamic changes of vegetation on the continent are also crucial for river ecosystem functions and related ecosystem services. In this paper, based on the Landsat image data from 1987 to 2020, we used the ArcGIS software to synthesize the bands and improved the normalized differential water index method and the object-oriented classification method, so as to obtain the forms of MCB and some vegetation classification vectors on the continents in the middle and lower reaches of the Yangtze River in the past 30 years. In addition, we compared the data with high spatial resolution images to verify the accuracy and reliability of the data. This dataset can be used for analysis of the evolution of MCB in the middle and lower reaches of the Yangtze River, analysis of the impact of environmental factors, and research on landscape pattern changes.