Seasonal mechanical behaviour of Elymus spec. for the assessment of ecosystem services

Wave attenuation by vegetation, such as in salt marshes or on coastal dunes, is an environmentally friendly measure for erosion control and coastal protection. A particular factor here is the seasonal variation, both on the plant side and on the wave side. Plants have different mechanical properties and physiology (including morphology, cellular and molecular characteristics) depending on the season. Mechanical experiments are essential to better evaluate the erosion protection provided by coastal vegetation depending on the season, and to generate mechanical properties for corresponding simulations that can predict the vegetation’s resistance to waves, which in turn would enable optimised planting. For this purpose, different bending experiments were performed on salt marsh culm sections collected at different times in the year. Based on the cross-sectional morphology and force–deflection curves, the non-linear structural and material behaviour of the culm section is obtained using the inverse finite element method. The results show that the upper part of the grass culm behaves much more softly than the middle and lower parts, while the culm has a much stiffer material behaviour in winter (March) than in summer (June and September). In addition, this study found a negative correlation between Young’s modulus and second moment of inertia, suggesting an adaptive trade-off between structural and material properties under different growth conditions. The data obtained are important for a general understanding of the seasonal behaviour of salt marsh vegetation. On the other hand, they are particularly valuable for modelling of coastal erosion, vegetation patches or culm-fluid interactions.