Under which conditions can tidal reeds contribute to shore protection? The critical interplay between external stress and internal stress resistance in brackish marshes

Abstract Tidal reeds provide essential coastal protection by shielding the shore from the effects of waves and currents, reducing soil erosion or even enabling sediment accretion. However, these environments face increasing threats from human activities and climate change. This study focuses on the Elbe estuary in Germany, investigating factors that influence tidal reed expansion and recession. We investigated the dynamics of three shore sections, comparing reed‐dominated and grassland‐dominated shore sections, and assessed their ability to attenuate waves and mitigate shoreline erosion. Our findings reveal significant differences in shoreline dynamics between the sites, influenced by factors such as hydrodynamic stress, vegetation cover, and sediment composition. In particular, we highlight how tidal reeds contribute to shore stabilization through wave attenuation and the strengthening effects of their root systems during periods of reduced plant biomass in winter. However, the effectiveness of reeds in shoreline protection depends on the level of external stress, particularly from storm surges, with areas exposed to higher hydrodynamic forces showing greater erosion. The study underscores the importance of maintaining tidal reeds for resilient coastal protection, while also acknowledging that external stress factors sometimes require supplementary measures to ensure long‐term shoreline stability. Our results contribute to a deeper understanding of estuarine shore dynamics and offer insights for future management strategies.