How does landscape vegetation configuration regulate local channel initiation in rapidly expanding marsh?

Biogeomorphic interactions between tidal channels and marsh plants play a crucial role in enhancing coastal resilience to climate change. Previous studies linking the channel formation with vegetation dynamics predominantly focused on the early initiation, characterized by local-scale plant-flow feedbacks. However, the influence of rapid changes in landscape-scale vegetation pattern on the channel initiation remains poorly understood, especially in micro-tidal system. In this study, we investigated this relationship through biogeomorphic modeling combined with the analysis of satellite images in a rapidly expanding marsh in China under Spartina alterniflora invasion. The satellite images demonstrated the increase in drainage density and the decrease in unchanneled path length following plant encroachment. Our modeling results showed that local flow acceleration between vegetation patches was insufficient to initiate channels rapidly before the merging of isolated patches under micro-tidal conditions. With plant expansion, the continuous marsh caused landscape flow diversion from homogenous platform flow to concentrated channel flow, which promoted evident tributary channel initiation in the landward marsh zone. The vegetation removal scenarios further highlighted that the flow divergence from adjacent platforms due to the spatial heterogeneity in plant configuration amplified the magnitude of local hydrodynamics and further channel incision. Our findings emphasize that the initiation of tidal channels not only depends on local plant-flow interaction but is largely driven by landscape vegetation configuration under micro-tidal conditions.