Plant trait trade‐offs regulate tidal marsh resistance to combined hydrodynamic and erosion stress

Abstract Tidal marshes are increasingly recognized for nature‐based shoreline protection. However, their ability to persist under changing environmental and climate conditions remains uncertain, particularly in response to combined stress from hydrodynamic forces (currents, waves) and sediment bed erosion. Conducting flume experiments, we evaluated the resistance of three marsh species ( S. tabernaemontani , B. maritimus and P. australis ), which naturally grow along a cross‐shore gradient from high to low hydrodynamic exposure, to combined stress from water flow and sediment erosion. We reveal distinct functional trade‐offs between above‐ground and below‐ground plant traits: species with flexible above‐ground shoots (here: S. tabernaemontani ) avoid hydrodynamic drag‐induced damage to shoots but are prone to uprooting due to shallow below‐ground root systems, while species with rigid stems and deep roots (here P. australis ) resist uprooting and dislodgement but experience higher hydrodynamic drag forces and hence suffer more from structural stem damage. B. maritimus exhibited intermediate traits, maintaining anchorage with minimal shoot damage, aligning with its occurrence at intermediate positions along hydrodynamic and erosion gradients in the field. These findings demonstrate that plant resistance to physical disturbance in tidal marshes arises from a balance between anchorage and mechanical stress avoidance, driven by variation in functional plant traits. Understanding this balance is crucial for predicting species zonation, persistence and the shoreline protection capacity of tidal marshes. Synthesis and applications . Our study highlights the importance of integrating both above‐ and below‐ground plant traits when assessing marsh resistance. Promoting plant species with complementary stress resistance traits along environmental gradients can enhance the shoreline protection functionality of tidal marshes under changing environmental and climate conditions.