The long-term legacy of riparian vegetation in a hydrogeomorphologically remodelled fluvial setting

The typical Japanese river maintains a vegetation-suppressive effect on riparian habitats. During recent decades, most Japanese rivers have encountered extensive human-induced alterations, and over time, the rivers have been transformed from unvegetated to vegetated. The lower Tedori River, which is a representative case of this phenomenon, is located in a region that exhibits signs of global climate change. According to quantitative analyses of sediment, the river corridor has historically reached an equilibrium since the prohibition of heavy sediment extraction activities, and the water discharge is stable because of dams. The contemporaneous vegetation encroachment was observed in a historical imagery survey and the vegetation dynamics of the river reach for the past 18 years were analysed to identify forcing hydro-climatic variables. The normalized difference vegetation index (NDVI) was adopted for the surveillance of vegetation dynamics, and multiple regression analysis was employed to evaluate its relationship with predictor variables. River water level was the strongest determinant of NDVI, with both Pearson correlation and standardized beta coefficients of -0.405, while air temperature was next, with values of 0.363 and 0.288, respectively. These findings were supported by the spatial distribution of temporally advancing vegetation patches determined using the aerial imagery and pixel value maxima of NDVI bands. In addition, the development of vegetation patches will presumably give rise to more pro-vegetation surroundings in the riparian zone through reciprocal linkages with hydrogeomorphic processes. These objective predictions may help inform the proactive planning for river and coastal management.