Study on the distribution characteristics of suitable vegetation growth areas on typical sand bars in the upper Jingjiang River based on remote sensing images
Mid-channel bars are important parts of floodplains in the middle reach of the Yangtze River.Clarifying the distribution characteristics of suitable vegetation growth areas on the bars and the critical conditions they should meet is a crucial prerequisite for ecological embankment planning and design,as well as vegetation changing trend prediction on the riverine floodplain after the operation of the Three Gorges Dam.In this study,Guanzhou Bar and Tuqizhou Bar,located in the Upper Jingjiang River,were selected as typical representatives of gravel and sand mid-channel bars,respectively.Long-time series of floodplain inundation and vegetation information from 1986 to 2002 were extracted based on Landsat remote sensing images.An improved method combining hydrological data and image data was used to calculate the inundation frequency and vegetation frequency of every pixel on the bar sur-face.The relationship between the two frequencies were analyzed,and the inundation frequency conditions for the suitable vegetation growth areas were determined.The research results indicate that both types of mid-channel bars have concentrated low and high vegetation frequency zones,while the medium vegetation frequency zone are more dispersed.Based on the distribution characteristics of vegetation frequency,the bar surface area can be divided into high coverage zone,medium coverage zone,transitional zone,and unsuitable vegetation zone,with the criti-cal vegetation frequency thresholds of 80％,50％,and 20％,respectively.The inundation frequencies at different locations on the bars are the dominant factor affecting vegetation frequency.On average over a long period,the in-undation frequency-vegetation frequency relationships on both types of bars follow a unified logistic curve.Accord-ing to this curve,critical inundation conditions for each zone are determined as an annual inundation duration of 18 days,43 days,and 92 days,respectively.At locations where the annual average inundation duration exceed 92 days,the vegetation frequency rapidly decreases to below 10％.The methods and findings in this paper can provide references for predicting the vegetation succession trend in dam downstream reaches after the impoundment of the Three Gorges Dam.
万方数据
维普
