The impact of vegetation on meandering rivers

The Palaeozoic evolution of land plants revolutionized river geomorphology. However, the relationships between biotic forcing and channel dynamics are still debated and, as such, the impacts of anthropogenic stressors such as climate change, reduced biodiversity and aridification on modern meandering rivers and their biogeochemical fluxes remain poorly understood. In this Review, we propose a unifying framework based on field and modelling data that describes the stability and dynamics of meandering rivers in both the presence and the absence of land plants. Based on evidence from the pre-vegetation rock record and from modern systems, we emphasize that meandering streams can indeed arise in the absence of land plants. However, plant evolution provided widespread settings suitable for stable meandering systems through retention of floodplain mud, sediment baffling and mechanical strengthening of channel banks. Altogether, these processes slowed the characteristic rates of meander growth and floodplain-soil reworking by up to an order of magnitude. Continued anthropogenic removal of riparian and watershed vegetation due to increased urbanization, deforestation, aridification and pollution could revert streams to pre-vegetation functioning, thereby increasing their channel and sediment mobility. Future research can use this framework to constrain the pace of ancient landscape processes on Earth and Mars, in addition to modern terrestrial rivers impacted by humans.