Channel geomorphology and riparian vegetation interactions along four anabranching reaches of the Upper Yellow River

Abstract

The fluvial biogeomorphic succession (FBS) phase model is used to appraise biogeomorphic interactions along four anabranching reaches of the Upper Yellow River. Geomorphic features and vegetation distribution patterns are combined to assess the dominant FBS phase. A notable increase in shrub and tree cover and a decrease in sedges occur with decreasing elevation from 4200 to 2200 m asl. The Maduo reach (4185 m) is characterized by the biogeomorphic phase, while the Dari (3960 m) reach is at the pioneer phase, with short shrubs playing a prominent role. Both the Maqu (3450 m) and the Guide (2117 m) reaches are ecological phase dominated (the Guide reach has been impacted by flow regulation in recent decades). Reaches other than the Maduo have experienced an increase in post-pioneer vegetation (woody plants) in recent decades, with a decrease in pioneer plant communities (grass and sedges). The Dari reach experienced the most dynamic channel planform changes, with a marked increase in short shrub patches from 2007 to 2017. An increase in woody vegetation underpinned increasingly stable geomorphic dynamics in the Maqu reach. Human activities have restricted geomorphic impacts of expanded areas of woody riparian vegetation in the Guide reach. Variability in dominant FBS phases exerts a primary control upon channel behavior and evolutionary traits in the four study reaches.