Scale-dependent biogeomorphic feedbacks control the tidal marsh evolution under Spartina alterniflora invasion.

The mechanisms of biogeomorphic feedbacks and its influencing factors have been extensively studied for pioneer species colonization in tidal environment. However, biogeomorphic impacts of alien species over the entire invasion process coupled with hydro-geomorphologic processes and ecoengineering traits still lack sufficient understanding to forecast salt marsh succession. In this study, we developed a bio-hydrogeomorphic model to account for the tidal platform evolution and vegetation distribution under Spartina alterniflora invasion in the Yellow River Delta, China. Our field observation and modelling results revealed that salt marsh transformed from a stabilized to a self-organized system due to the significant geomorphic-biological feedback under Spartina alterniflora invasion. Tidal channels took shape differently along the elevation gradient of the intertidal platform. Patch-scale feedbacks promoted the channel initiation in the low-elevated zone during early colonization phase. While landscape-scale feedbacks dominated channel incision in the middle to high platform during the mature phase. Specifically, the channel initiation in the middle-elevated ecotone could be attributed to the change from homogenous sheet flow to concentrated channel flow along the marsh edge, which was determined by tidal prism and discrepancy in organism traits. Hence, our study showed that scale-dependent feedback and gaps in ecoengineering capacity of organism determined the morphological variation in the invasive ecosystem. This would provide the insights into biogeomorphic impacts of invasive species and scientific conservation for native ecosystems.