Our study aims to enhance process understanding of the long-term (decadal and longer) cyclic marsh

dynamics by identifying the mechanisms that translate large-scale physical forcing in the system into vegetation

change, in particular (i) the initiation of lateral erosion on an expanding marsh, and (ii) the control of

seedling establishment in front of an eroding marsh-cliff. Short-term sediment dynamics (i.e., seasonal and

shorter changes in sediment elevation) at the mudflat causes variation in mudflat elevation over time (dzTF).

The resulting difference in elevation between the tidal flat and adjacent marsh (DZ) initiates lateral marsh

erosion. Marsh erosion rate was found to depend on sediment type and to increase with increasing DZ and

hydrodynamic exposure. Laboratory and field experiments revealed that seedling establishment was negatively

impacted by an increasing dzTF. As the amplitude of dzTF increases towards the channel, expanding

marshes become more prone to lateral erosion the further they extend on a tidal flat, and the chance for

seedlings to establish increases with the distance that marsh has eroded back towards the land. This process-based

understanding, showing the role of sediment dynamics as explanatory factor for marsh cyclicity, is

important for protecting and restoring valuable marsh ecosystems. Overall, our experiments emphasize the

need for understanding the connections between neighbouring ecosystems such as mudflat and salt marsh.